Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005576 extracellular region	IBA GO_REF:0000033	REMOVE	Summary: CKM is a cytosolic enzyme; this IBA "is_active_in extracellular region" is an over-propagation through the phylogenetic tree. Reason: CKM/CK-MM is a cytosolic creatine kinase (UniProt SUBCELLULAR LOCATION: Cytoplasm) that functions intracellularly in the phosphocreatine shuttle and at the myofibrillar M-band. Serum/extracellular CK is enzyme leakage from damaged muscle, not a secreted, extracellularly-active form. An "is_active_in extracellular region" assertion is biologically incorrect for the cytosolic CK reaction and is an electronic (IBA) over-propagation, so it is removed.
GO:0004111 creatine kinase activity	IBA GO_REF:0000033	ACCEPT	Summary: Creatine kinase activity is the defining molecular function of CKM; strongly supported across evidence types. Reason: CKM catalyzes the reversible creatine + ATP <-> phosphocreatine + ADP reaction (EC 2.7.3.2). This phylogenetic (IBA) annotation is concordant with the experimental/structural and sequence evidence and represents the core molecular function. Supporting Evidence: PMID:3778496 A full length cDNA for human M creatine kinase has been isolated and sequenced.
GO:0046314 phosphocreatine biosynthetic process	IBA GO_REF:0000033	ACCEPT	Summary: CKM catalyzes the reaction that produces phosphocreatine; this is the direct biological-process correlate of its molecular function. Reason: The creatine kinase reaction is reversible; in the phosphocreatine-synthesizing direction CKM produces N-phosphocreatine from creatine and ATP, justifying involvement in phosphocreatine biosynthetic process. The physiologically dominant cytosolic role is the reverse (ATP regeneration), but this BP term is the established correlate of creatine kinase activity and is accepted as core.
GO:0003824 catalytic activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Correct but uninformatively general; a high-level parent of creatine kinase activity. Reason: "catalytic activity" (GO:0003824) is a root-level MF parent that is true but adds no information beyond the specific creatine kinase activity (GO:0004111) already annotated. It is an InterPro2GO electronic generalization subsumed by the specific term.
GO:0004111 creatine kinase activity	IEA GO_REF:0000120	ACCEPT	Summary: Correct core molecular function (electronic call from Rhea/EC mapping). Reason: This IEA annotation derives from the Rhea/EC 2.7.3.2 mapping to creatine kinase activity and agrees with the experimental and phylogenetic evidence for the same term. Retained as a correct statement of the core function.
GO:0005737 cytoplasm	IEA GO_REF:0000044	MODIFY	Summary: Correct localization, but the more specific cytosol term is preferable. Reason: CKM is a soluble cytosolic enzyme. UniProt records SUBCELLULAR LOCATION as Cytoplasm, and Reactome annotates the more specific cytosol (GO:0005829). The broad "cytoplasm" should be refined to cytosol, which is also where the phosphocreatine-shuttle reaction occurs. Proposed replacements: cytosol
GO:0016301 kinase activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Correct but over-general parent of creatine kinase activity. Reason: "kinase activity" (GO:0016301) is a general parent subsumed by the specific creatine kinase activity (GO:0004111). It is an InterPro2GO electronic generalization adding no specificity.
GO:0016772 transferase activity, transferring phosphorus-containing groups	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Correct but over-general parent of creatine kinase activity. Reason: A high-level transferase parent term subsumed by the specific creatine kinase activity (GO:0004111); InterPro2GO electronic generalization with no added information.
GO:0016775 phosphotransferase activity, nitrogenous group as acceptor	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Accurate intermediate parent (creatine's guanidino nitrogen is the acceptor) but still less informative than creatine kinase activity. Reason: Creatine kinase is indeed a phosphotransferase with a nitrogenous group as acceptor, so this term is biologically accurate, but it is a parent of the specific creatine kinase activity (GO:0004111) and is an electronic generalization that does not add information over the specific term.
GO:0046314 phosphocreatine biosynthetic process	IEA GO_REF:0000002	ACCEPT	Summary: Correct biological process (electronic call), duplicating the accepted IBA annotation. Reason: InterPro2GO electronic annotation to the same biological process supported by the IBA annotation; consistent with the creatine kinase reaction and accepted.
GO:0005515 protein binding	IPI PMID:21516116 Next-generation sequencing to generate interactome datasets.	KEEP AS NON CORE	Summary: Uninformative bare "protein binding"; supports a real interaction (ASB9) but not a core function. Reason: Bare "protein binding" (GO:0005515) is uninformative per curation guidelines. The underlying IntAct interaction (with ASB9, Q96DX5) is real, so the annotation is kept but marked non-core; it does not describe CKM's catalytic function.
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" from a proteome-scale interactome (ASB9). Reason: Real binary interaction evidence (CKM-ASB9, Q96DX5) but the term itself is uninformative; kept as non-core supporting evidence rather than a core function.
GO:0005515 protein binding	IPI PMID:28514442 Architecture of the human interactome defines protein commun...	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" from an interactome map (CKB, ASB9). Reason: Supports interactions with CKB (P12277; consistent with CK-MB heterodimer formation) and ASB9 (Q96DX5). The CKB partnership is biologically meaningful but "protein binding" is uninformative; kept as non-core.
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" from the HuRI binary interactome (CKMT1B, ASB9). Reason: Supports interactions with mitochondrial CK (CKMT1B, P12532) and ASB9 (Q96DX5). Real partner evidence but uninformative term; kept as non-core.
GO:0005515 protein binding	IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ...	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" (huntingtin interaction). Reason: Supports a CKM-huntingtin (HTT, P42858) interaction reported in a neurodegeneration interactome. Real partner evidence but uninformative term; kept as non-core.
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" from BioPlex (CKB, ASB9). Reason: Supports interactions with CKB (P12277) and ASB9 (Q96DX5). Real partner evidence but uninformative term; kept as non-core.
GO:0005515 protein binding	IPI PMID:35271311 OpenCell: Endogenous tagging for the cartography of human ce...	KEEP AS NON CORE	Summary: Uninformative bare "protein binding" from OpenCell (CKB). Reason: Supports a CKM-CKB (P12277) interaction consistent with CK-MB heterodimer formation. Real partner evidence but uninformative term; kept as non-core.
GO:0005576 extracellular region	IEA GO_REF:0000107	REMOVE	Summary: CKM is cytosolic; extracellular localization is an electronic ortholog-transfer error. Reason: This Ensembl-Compara electronic transfer asserts extracellular localization, but CKM is a cytosolic enzyme (UniProt: Cytoplasm). Extracellular CK is leakage from damaged cells rather than a functional secreted location. Removed as an incorrect electronic (IEA) over-propagation.
GO:0004111 creatine kinase activity	ISS GO_REF:0000024	ACCEPT	Summary: Core molecular function, supported by sequence similarity to a well-characterized ortholog. Reason: ISS transfer from UniProtKB:P00563 (rabbit M-CK) to the same creatine kinase activity term; concordant with all other evidence for the core function.
GO:0005829 cytosol	TAS Reactome:R-HSA-200318	ACCEPT	Summary: Correct, specific subcellular location where the creatine kinase reaction occurs. Reason: Reactome (TAS) places CKM in the cytosol for the creatine + ATP => phosphocreatine + ADP reaction. This matches UniProt (Cytoplasm) and is the appropriate specific location for the cytosolic limb of the phosphocreatine shuttle.
GO:0005515 protein binding	IPI PMID:12972258 Muscle-type creatine kinase interacts with central domains o...	KEEP AS NON CORE	Summary: Uninformative bare "protein binding", but underlies a functionally important M-band interaction (myomesin/M-protein). Reason: The underlying interaction is biologically significant - MM-CK binds the central domains of the M-band proteins myomesin and M-protein, anchoring it at the sarcomeric M-band where it regenerates ATP for the myosin ATPase. However, the bare "protein binding" term is uninformative; the functional content is captured in core_functions (M band location) rather than as a core MF here. Supporting Evidence: PMID:12972258 A yeast two-hybrid screen led to the identification of MM-CK as a binding partner of a central portion of myomesin (My7-8). An interaction was observed with domains six to eight of the closely related M-protein
GO:0004111 creatine kinase activity	TAS PMID:3778496 Isolation and sequence analysis of a full-length cDNA for hu...	ACCEPT	Summary: Core molecular function asserted by the original human M-CK characterization. Reason: Traceable author statement (TAS) for creatine kinase activity from the human M-CK cDNA/sequence paper. Confirms the core molecular function. Supporting Evidence: PMID:3778496 A full length cDNA for human M creatine kinase has been isolated and sequenced.
GO:0031430 M band	IPI PMID:12972258 Muscle-type creatine kinase interacts with central domains o...	NEW	Summary: A functionally important pool of CK-MM localizes to the sarcomeric M-band, where it binds myomesin and M-protein and regenerates ATP for the myosin ATPase. Reason: Not present in the seeded GOA, but well supported experimentally: MM-CK binds the M-band of sarcomeric muscle in an isoform-specific manner via its M-specific N-terminal lysines, interacting with central domains of myomesin and M-protein, and serves there as an intramyofibrillar ATP regenerator. This is a key structural/functional localization for the muscle isoform and is proposed as a new localization annotation. Supporting Evidence: PMID:12972258 MM-CK interacts in an isoform-specific manner with the M-band of sarcomeric muscle, where it serves as an efficient intramyofibrillar ATP-regenerating system for the actin-activated myosin ATPase located nearby on both sides of the M-band.

Core Functions

Cytosolic creatine kinase activity: CKM (as CK-MM homodimer or CK-MB heterodimer with CKB) reversibly transfers a phosphoryl group between ATP and creatine, regenerating ATP from phosphocreatine at sites of high ATP turnover in striated muscle.

Molecular Function:

creatine kinase activity

Directly Involved In:

phosphocreatine biosynthetic process

Cellular Locations:

cytosol

Supporting Evidence:

Reactome:R-HSA-200318
creatine + ATP => phosphocreatine + ADP [CKB,CKM]
PMID:3778496
A full length cDNA for human M creatine kinase has been isolated and sequenced.

M-band-localized creatine kinase: a functionally important pool of CK-MM binds the sarcomeric M-band (via central domains of myomesin and M-protein), where it acts as an intramyofibrillar ATP regenerator coupled to the actin-activated myosin ATPase - the receiving end of the phosphocreatine shuttle.

Molecular Function:

creatine kinase activity

Cellular Locations:

M band

Supporting Evidence:

PMID:12972258
MM-CK interacts in an isoform-specific manner with the M-band of sarcomeric muscle, where it serves as an efficient intramyofibrillar ATP-regenerating system for the actin-activated myosin ATPase located nearby on both sides of the M-band.

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:12972258

Muscle-type creatine kinase interacts with central domains of the M-band proteins myomesin and M-protein.

MM-CK binds the sarcomeric M-band in an isoform-specific manner and acts as an intramyofibrillar ATP-regenerating system for the nearby actin-activated myosin ATPase.

"MM-CK interacts in an isoform-specific manner with the M-band of sarcomeric muscle, where it serves as an efficient intramyofibrillar ATP-regenerating system for the actin-activated myosin ATPase located nearby on both sides of the M-band."
MM-CK binds central domains of myomesin (My7-8) and of the related M-protein (domains six to eight), identifying its M-band binding partners.

"A yeast two-hybrid screen led to the identification of MM-CK as a binding partner of a central portion of myomesin (My7-8). An interaction was observed with domains six to eight of the closely related M-protein"

PMID:21516116

Next-generation sequencing to generate interactome datasets.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:28514442

Architecture of the human interactome defines protein communities and disease networks.

PMID:32296183

A reference map of the human binary protein interactome.

PMID:32814053

Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains.

PMID:33961781

Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.

PMID:35271311

OpenCell: Endogenous tagging for the cartography of human cellular organization.

PMID:3778496

Isolation and sequence analysis of a full-length cDNA for human M creatine kinase.

Reports the full-length cDNA and coding sequence for human M-type creatine kinase, with strong cross-species conservation of the enzyme.

"A full length cDNA for human M creatine kinase has been isolated and sequenced."

Reactome:R-HSA-200318

creatine + ATP => phosphocreatine + ADP [CKB,CKM]

Suggested Experiments

Experiment: Express wild-type CKM and an M-band-binding-deficient lysine mutant (K8/K24/K104/K115) in muscle cells or Ckm-null myofibers, confirm equal intrinsic creatine kinase activity in vitro, then compare M-band localization (immuno-EM), contractile ATP/ADP buffering, and fatigue resistance during burst activity.

Hypothesis: M-band binding of CK-MM, mediated by the four M-specific N-terminal lysines (K8, K24, K104, K115), is required for efficient ATP regeneration at the myofibril rather than for catalysis per se.

Type: structure-function / localization

📚 Additional Documentation

Notes

(CKM-notes.md)

CKM (Creatine kinase M-type) — Gene Review Notes

UniProt: P06732 (KCRM_HUMAN). Gene: CKM (synonym CKMM). HGNC:1994. EC 2.7.3.2.
Located on chromosome 19q13. 381 aa cytosolic protein.

Catalytic function and reaction

CKM is the muscle-type cytosolic creatine kinase. It reversibly catalyzes phosphoryl
transfer between ATP and creatine:

creatine + ATP = N-phosphocreatine + ADP + H(+) [Rhea:RHEA:17157, EC=2.7.3.2]
(UniProt CATALYTIC ACTIVITY, P06732)

UniProt FUNCTION: "Reversibly catalyzes the transfer of phosphate between ATP and various
phosphogens (e.g. creatine phosphate). Creatine kinase isoenzymes play a central role in
energy transduction in tissues with large, fluctuating energy demands, such as skeletal
muscle, heart, brain and spermatozoa." (P06732, by similarity to P00563).

The reaction is reversible; the physiological direction depends on local energy state.
In the cytosolic/myofibrillar limb of the phosphocreatine shuttle, CKM regenerates ATP
from phosphocreatine (PCr + ADP -> ATP + Cr) at sites of high ATPase activity, while
mitochondrial CK (CKMT) runs the reaction in the synthetic direction near the ATP source.
Membership of the ATP:guanido phosphotransferase family (UniProt SIMILARITY).

Dimer composition (MM / MB)

UniProt SUBUNIT: "Dimer of identical or non-identical chains, which can be either B (brain
type) or M (muscle type). With MM being the major form in skeletal muscle and myocardium,
MB existing in myocardium, and BB existing in many tissues, especially brain." (P06732).

So CKM forms CK-MM homodimers (the dominant species in skeletal muscle and myocardium) and
CK-MB heterodimers with CKB (P12277, brain-type) in myocardium. The CKM/CKB interaction is
recorded in UniProt INTERACTION (P06732; P12277: CKB). CKM also interacts with mitochondrial
CK (CKMT1B, P12532), the ankyrin-repeat protein ASB9 (Q96DX5), and huntingtin (HTT, P42858).

Localization: M-band / myofibrils and membranes

MM-CK is a bona fide cytosolic enzyme (UniProt SUBCELLULAR LOCATION: Cytoplasm) but a
functionally important pool is bound at the sarcomeric M-band, where it acts as a local
ATP regenerator coupled to the myosin ATPase.

PMID:12972258

PMID:12972258 — these four M-specific N-terminal lysines mediate the M-band charge-clamp
binding (also covered by PMC2175123, Hornemann et al.).

Historical primary evidence for M-line CK as the receiving end of the shuttle: PMID:6143755
("Function of M-line-bound creatine kinase as intramyofibrillar ATP regenerator at the
receiving end of the phosphorylcreatine shuttle in muscle"). MM-CK is additionally found
associated with the sarcoplasmic reticulum and T-tubule membranes, where it supports local
ATP/ADP ratios for Ca2+ pumping (review/biochemical literature; not a CKM-specific cached PMID).

Energy buffering / phosphocreatine shuttle

CK isoenzymes buffer cytosolic ATP and shuttle high-energy phosphate between mitochondria
(site of PCr synthesis by mitochondrial CK) and sites of ATP consumption (myofibrils,
sarcolemmal/SR ion pumps), where cytosolic CKM regenerates ATP. This temporal (buffering)
and spatial (shuttle) role is the core physiological function of the CK system in striated
muscle, heart, and other high-energy-demand tissues (UniProt FUNCTION; review literature).

Tissue expression

Human Protein Atlas: "Group enriched (skeletal muscle, tongue)" (UniProt HPA line).
Bgee: expressed in skeletal muscle and many other tissues. CKM is the muscle-specific
isoform, highly expressed in skeletal muscle and cardiac muscle (myocardium). Its gene is
developmentally regulated and tissue-specific (PMID:2903158, "Developmental regulation and
tissue-specific expression of the human muscle creatine kinase gene"). The MCK enhancer/
promoter is a classic muscle-specific regulatory element.

Disease / physiology

Serum CK-MM and CK-MB are classic clinical biomarkers: total CK and CK-MB rise after
myocardial infarction and CK-MM after skeletal-muscle injury (rhabdomyolysis, muscular
dystrophy). MIM:123310 (gene). A common CKM 3'-UTR polymorphism (NcoI) has been associated
with variation in exercise/endurance phenotypes in some studies. CKM is a drug-interaction
target (creatine, phosphocreatine in DrugBank). No classical Mendelian disease is firmly
attributed to CKM loss-of-function in humans; Ckm-knockout mice are viable but show altered
muscle energetics and burst-activity performance.

Structure

Two-domain phosphagen kinase fold: N-terminal phosphagen kinase domain (res 11-98) and
C-terminal catalytic domain (res 125-367). ATP-binding residues annotated (128-132, 191,
236, 292, 320-325, 335). Crystal structures: 1I0E (3.5 Å human MM-CK), 7BF2 (peptide).

GO review orientation

Core MF: creatine kinase activity (GO:0004111) — strongly supported (catalytic activity,
Rhea/EC mapping, ISS from P00563, TAS PMID:3778496, IBA). ACCEPT.
Core BP: phosphocreatine biosynthetic process (GO:0046314) — the cytosolic enzyme
catalyzes the reversible reaction whose "biosynthetic" labelled direction is PCr synthesis;
appropriate, ACCEPT (the reverse direction is the ATP-regenerating physiological role).
Core CC: cytosol (GO:0005829, TAS Reactome) / cytoplasm; M band (GO:0031430) supported by
PMID:12972258 isoform-specific M-band binding.
ATP binding (GO:0005524, KW IEA) — true, but a generic supporting MF; KEEP_AS_NON_CORE.
Generic IEA parents (catalytic activity GO:0003824, kinase activity GO:0016301, transferase
GO:0016772, phosphotransferase nitrogenous acceptor GO:0016775) — true but uninformative
parents of creatine kinase activity; MARK_AS_OVER_ANNOTATED / generalizations subsumed by
GO:0004111.
extracellular region / extracellular space (GO:0005576 IBA & IEA) — CKM is a cytosolic
enzyme; serum CK is leakage from damaged cells, not secretion. The IBA "is_active_in
extracellular region" is an over-propagation. CKM is not active extracellularly. MARK_AS_
OVER_ANNOTATED / REMOVE candidate (IBA/IEA, electronic, arguable on biological grounds).
protein binding (GO:0005515, many IPI) — uninformative bare term; the informative ones
(M-band myomesin/M-protein PMID:12972258; CKB; CKMT1B; ASB9; HTT) are captured by SUBUNIT/
interaction. KEEP_AS_NON_CORE (avoid as core function per guidelines).

📄 View Raw YAML

id: P06732
gene_symbol: CKM
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  CKM encodes the muscle-type (M-type) cytosolic creatine kinase (EC 2.7.3.2), a
  member of the ATP:guanido phosphotransferase (phosphagen kinase) family. It
  reversibly catalyzes the transfer of a phosphoryl group between ATP and
  creatine (creatine + ATP <-> N-phosphocreatine + ADP + H+). The enzyme is a
  dimer: CK-MM homodimers are the dominant form in skeletal muscle and
  myocardium, and CK-MB heterodimers with the brain-type subunit CKB occur in
  myocardium. Together with mitochondrial creatine kinase, cytosolic CKM forms
  the cytosolic limb of the phosphocreatine (PCr) energy-shuttle and ATP-buffering
  system, regenerating ATP from phosphocreatine at sites of high ATP turnover such
  as the myofibrillar myosin ATPase and membrane ion pumps. A functionally
  important pool of CK-MM is bound at the sarcomeric M-band through M-specific
  N-terminal lysine residues that interact with the central domains of the
  M-band proteins myomesin and M-protein, positioning it as an intramyofibrillar
  ATP regenerator. CKM is highly and selectively expressed in skeletal and
  cardiac muscle; its serum activity (CK-MM, CK-MB) is a clinical marker of
  skeletal-muscle and myocardial injury.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:12972258
  title: Muscle-type creatine kinase interacts with central domains of the M-band
    proteins myomesin and M-protein.
  findings:
  - statement: MM-CK binds the sarcomeric M-band in an isoform-specific manner and acts
      as an intramyofibrillar ATP-regenerating system for the nearby actin-activated
      myosin ATPase.
    supporting_text: MM-CK interacts in an isoform-specific manner with the M-band of
      sarcomeric muscle, where it serves as an efficient intramyofibrillar
      ATP-regenerating system for the actin-activated myosin ATPase located nearby on
      both sides of the M-band.
    reference_section_type: ABSTRACT
  - statement: MM-CK binds central domains of myomesin (My7-8) and of the related
      M-protein (domains six to eight), identifying its M-band binding partners.
    supporting_text: A yeast two-hybrid screen led to the identification of MM-CK as a
      binding partner of a central portion of myomesin (My7-8). An interaction was
      observed with domains six to eight of the closely related M-protein
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified abstract; directly establishes isoform-specific
      M-band localization of MM-CK and its ATP-regenerating role at the myofibril, and
      identifies myomesin/M-protein as binding partners.
- id: PMID:21516116
  title: Next-generation sequencing to generate interactome datasets.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome method paper supporting an IntAct
      CKM-ASB9 (Q96DX5) interaction; informative for partner identity only, not for
      CKM's core enzymatic function.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Proteome-scale Y2H interactome; supports a binary CKM-ASB9 interaction
      via IntAct. Background partner evidence, not core-function evidence.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome map supporting CKM interactions (CKB
      P12277 and ASB9 Q96DX5). Background partner evidence.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: HuRI binary interactome; supports CKM interactions (CKMT1B P12532 and
      ASB9 Q96DX5). Background partner evidence.
- id: PMID:32814053
  title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins
    and Uncovers Widespread Protein Aggregation in Affected Brains.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Neurodegeneration-focused interactome supporting a CKM-huntingtin
      (HTT P42858) interaction via IntAct. Background partner evidence.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: BioPlex proteome-scale interactome supporting CKM interactions (CKB
      P12277 and ASB9 Q96DX5). Background partner evidence.
- id: PMID:35271311
  title: 'OpenCell: Endogenous tagging for the cartography of human cellular organization.'
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: OpenCell endogenous-tagging interactome supporting a CKM-CKB (P12277)
      interaction. Background partner evidence consistent with CK-MB heterodimer
      formation.
- id: PMID:3778496
  title: Isolation and sequence analysis of a full-length cDNA for human M creatine
    kinase.
  findings:
  - statement: Reports the full-length cDNA and coding sequence for human M-type
      creatine kinase, with strong cross-species conservation of the enzyme.
    supporting_text: A full length cDNA for human M creatine kinase has been isolated and
      sequenced.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Original human M-CK cDNA/sequence paper; the basis for the TAS
      creatine kinase activity annotation.
- id: Reactome:R-HSA-200318
  title: creatine + ATP => phosphocreatine + ADP [CKB,CKM]
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Reactome reaction record for the cytosolic creatine kinase reaction;
      supports cytosol localization and the creatine kinase reaction for CKM/CKB.
existing_annotations:
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: CKM is a cytosolic enzyme; this IBA "is_active_in extracellular region" is
      an over-propagation through the phylogenetic tree.
    action: REMOVE
    reason: >-
      CKM/CK-MM is a cytosolic creatine kinase (UniProt SUBCELLULAR LOCATION:
      Cytoplasm) that functions intracellularly in the phosphocreatine shuttle and at
      the myofibrillar M-band. Serum/extracellular CK is enzyme leakage from damaged
      muscle, not a secreted, extracellularly-active form. An "is_active_in
      extracellular region" assertion is biologically incorrect for the cytosolic CK
      reaction and is an electronic (IBA) over-propagation, so it is removed.
- term:
    id: GO:0004111
    label: creatine kinase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Creatine kinase activity is the defining molecular function of CKM;
      strongly supported across evidence types.
    action: ACCEPT
    reason: >-
      CKM catalyzes the reversible creatine + ATP <-> phosphocreatine + ADP reaction
      (EC 2.7.3.2). This phylogenetic (IBA) annotation is concordant with the
      experimental/structural and sequence evidence and represents the core molecular
      function.
    supported_by:
    - reference_id: PMID:3778496
      supporting_text: A full length cDNA for human M creatine kinase has been isolated and
        sequenced.
- term:
    id: GO:0046314
    label: phosphocreatine biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: CKM catalyzes the reaction that produces phosphocreatine; this is the
      direct biological-process correlate of its molecular function.
    action: ACCEPT
    reason: >-
      The creatine kinase reaction is reversible; in the phosphocreatine-synthesizing
      direction CKM produces N-phosphocreatine from creatine and ATP, justifying
      involvement in phosphocreatine biosynthetic process. The physiologically dominant
      cytosolic role is the reverse (ATP regeneration), but this BP term is the
      established correlate of creatine kinase activity and is accepted as core.
- term:
    id: GO:0003824
    label: catalytic activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Correct but uninformatively general; a high-level parent of creatine
      kinase activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      "catalytic activity" (GO:0003824) is a root-level MF parent that is true but adds
      no information beyond the specific creatine kinase activity (GO:0004111) already
      annotated. It is an InterPro2GO electronic generalization subsumed by the specific
      term.
- term:
    id: GO:0004111
    label: creatine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Correct core molecular function (electronic call from Rhea/EC mapping).
    action: ACCEPT
    reason: >-
      This IEA annotation derives from the Rhea/EC 2.7.3.2 mapping to creatine kinase
      activity and agrees with the experimental and phylogenetic evidence for the same
      term. Retained as a correct statement of the core function.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Correct localization, but the more specific cytosol term is preferable.
    action: MODIFY
    reason: >-
      CKM is a soluble cytosolic enzyme. UniProt records SUBCELLULAR LOCATION as
      Cytoplasm, and Reactome annotates the more specific cytosol (GO:0005829). The
      broad "cytoplasm" should be refined to cytosol, which is also where the
      phosphocreatine-shuttle reaction occurs.
    proposed_replacement_terms:
    - id: GO:0005829
      label: cytosol
- term:
    id: GO:0016301
    label: kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Correct but over-general parent of creatine kinase activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      "kinase activity" (GO:0016301) is a general parent subsumed by the specific
      creatine kinase activity (GO:0004111). It is an InterPro2GO electronic
      generalization adding no specificity.
- term:
    id: GO:0016772
    label: transferase activity, transferring phosphorus-containing groups
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Correct but over-general parent of creatine kinase activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      A high-level transferase parent term subsumed by the specific creatine kinase
      activity (GO:0004111); InterPro2GO electronic generalization with no added
      information.
- term:
    id: GO:0016775
    label: phosphotransferase activity, nitrogenous group as acceptor
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Accurate intermediate parent (creatine's guanidino nitrogen is the
      acceptor) but still less informative than creatine kinase activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Creatine kinase is indeed a phosphotransferase with a nitrogenous group as
      acceptor, so this term is biologically accurate, but it is a parent of the
      specific creatine kinase activity (GO:0004111) and is an electronic
      generalization that does not add information over the specific term.
- term:
    id: GO:0046314
    label: phosphocreatine biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: Correct biological process (electronic call), duplicating the accepted IBA
      annotation.
    action: ACCEPT
    reason: >-
      InterPro2GO electronic annotation to the same biological process supported by the
      IBA annotation; consistent with the creatine kinase reaction and accepted.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:21516116
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding"; supports a real interaction (ASB9)
      but not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Bare "protein binding" (GO:0005515) is uninformative per curation guidelines. The
      underlying IntAct interaction (with ASB9, Q96DX5) is real, so the annotation is
      kept but marked non-core; it does not describe CKM's catalytic function.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" from a proteome-scale interactome
      (ASB9).
    action: KEEP_AS_NON_CORE
    reason: >-
      Real binary interaction evidence (CKM-ASB9, Q96DX5) but the term itself is
      uninformative; kept as non-core supporting evidence rather than a core function.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" from an interactome map (CKB, ASB9).
    action: KEEP_AS_NON_CORE
    reason: >-
      Supports interactions with CKB (P12277; consistent with CK-MB heterodimer
      formation) and ASB9 (Q96DX5). The CKB partnership is biologically meaningful but
      "protein binding" is uninformative; kept as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" from the HuRI binary interactome
      (CKMT1B, ASB9).
    action: KEEP_AS_NON_CORE
    reason: >-
      Supports interactions with mitochondrial CK (CKMT1B, P12532) and ASB9 (Q96DX5).
      Real partner evidence but uninformative term; kept as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" (huntingtin interaction).
    action: KEEP_AS_NON_CORE
    reason: >-
      Supports a CKM-huntingtin (HTT, P42858) interaction reported in a
      neurodegeneration interactome. Real partner evidence but uninformative term; kept
      as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" from BioPlex (CKB, ASB9).
    action: KEEP_AS_NON_CORE
    reason: >-
      Supports interactions with CKB (P12277) and ASB9 (Q96DX5). Real partner evidence
      but uninformative term; kept as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35271311
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding" from OpenCell (CKB).
    action: KEEP_AS_NON_CORE
    reason: >-
      Supports a CKM-CKB (P12277) interaction consistent with CK-MB heterodimer
      formation. Real partner evidence but uninformative term; kept as non-core.
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: CKM is cytosolic; extracellular localization is an electronic
      ortholog-transfer error.
    action: REMOVE
    reason: >-
      This Ensembl-Compara electronic transfer asserts extracellular localization, but
      CKM is a cytosolic enzyme (UniProt: Cytoplasm). Extracellular CK is leakage from
      damaged cells rather than a functional secreted location. Removed as an incorrect
      electronic (IEA) over-propagation.
- term:
    id: GO:0004111
    label: creatine kinase activity
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: enables
  review:
    summary: Core molecular function, supported by sequence similarity to a
      well-characterized ortholog.
    action: ACCEPT
    reason: >-
      ISS transfer from UniProtKB:P00563 (rabbit M-CK) to the same creatine kinase
      activity term; concordant with all other evidence for the core function.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-200318
  qualifier: located_in
  review:
    summary: Correct, specific subcellular location where the creatine kinase reaction
      occurs.
    action: ACCEPT
    reason: >-
      Reactome (TAS) places CKM in the cytosol for the creatine + ATP =>
      phosphocreatine + ADP reaction. This matches UniProt (Cytoplasm) and is the
      appropriate specific location for the cytosolic limb of the phosphocreatine
      shuttle.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12972258
  qualifier: enables
  review:
    summary: Uninformative bare "protein binding", but underlies a functionally
      important M-band interaction (myomesin/M-protein).
    action: KEEP_AS_NON_CORE
    reason: >-
      The underlying interaction is biologically significant - MM-CK binds the central
      domains of the M-band proteins myomesin and M-protein, anchoring it at the
      sarcomeric M-band where it regenerates ATP for the myosin ATPase. However, the
      bare "protein binding" term is uninformative; the functional content is captured
      in core_functions (M band location) rather than as a core MF here.
    supported_by:
    - reference_id: PMID:12972258
      supporting_text: A yeast two-hybrid screen led to the identification of MM-CK as a
        binding partner of a central portion of myomesin (My7-8). An interaction was
        observed with domains six to eight of the closely related M-protein
- term:
    id: GO:0004111
    label: creatine kinase activity
  evidence_type: TAS
  original_reference_id: PMID:3778496
  qualifier: enables
  review:
    summary: Core molecular function asserted by the original human M-CK
      characterization.
    action: ACCEPT
    reason: >-
      Traceable author statement (TAS) for creatine kinase activity from the human M-CK
      cDNA/sequence paper. Confirms the core molecular function.
    supported_by:
    - reference_id: PMID:3778496
      supporting_text: A full length cDNA for human M creatine kinase has been isolated and
        sequenced.
- term:
    id: GO:0031430
    label: M band
  evidence_type: IPI
  original_reference_id: PMID:12972258
  qualifier: located_in
  review:
    summary: A functionally important pool of CK-MM localizes to the sarcomeric M-band,
      where it binds myomesin and M-protein and regenerates ATP for the myosin ATPase.
    action: NEW
    reason: >-
      Not present in the seeded GOA, but well supported experimentally: MM-CK binds the
      M-band of sarcomeric muscle in an isoform-specific manner via its M-specific
      N-terminal lysines, interacting with central domains of myomesin and M-protein,
      and serves there as an intramyofibrillar ATP regenerator. This is a key
      structural/functional localization for the muscle isoform and is proposed as a
      new localization annotation.
    supported_by:
    - reference_id: PMID:12972258
      supporting_text: MM-CK interacts in an isoform-specific manner with the M-band of
        sarcomeric muscle, where it serves as an efficient intramyofibrillar
        ATP-regenerating system for the actin-activated myosin ATPase located nearby on
        both sides of the M-band.
core_functions:
- description: >-
    Cytosolic creatine kinase activity: CKM (as CK-MM homodimer or CK-MB
    heterodimer with CKB) reversibly transfers a phosphoryl group between ATP and
    creatine, regenerating ATP from phosphocreatine at sites of high ATP turnover
    in striated muscle.
  molecular_function:
    id: GO:0004111
    label: creatine kinase activity
  directly_involved_in:
  - id: GO:0046314
    label: phosphocreatine biosynthetic process
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: Reactome:R-HSA-200318
    supporting_text: creatine + ATP => phosphocreatine + ADP [CKB,CKM]
  - reference_id: PMID:3778496
    supporting_text: A full length cDNA for human M creatine kinase has been isolated and
      sequenced.
- description: >-
    M-band-localized creatine kinase: a functionally important pool of CK-MM binds
    the sarcomeric M-band (via central domains of myomesin and M-protein), where it
    acts as an intramyofibrillar ATP regenerator coupled to the actin-activated
    myosin ATPase - the receiving end of the phosphocreatine shuttle.
  molecular_function:
    id: GO:0004111
    label: creatine kinase activity
  locations:
  - id: GO:0031430
    label: M band
  supported_by:
  - reference_id: PMID:12972258
    supporting_text: MM-CK interacts in an isoform-specific manner with the M-band of
      sarcomeric muscle, where it serves as an efficient intramyofibrillar
      ATP-regenerating system for the actin-activated myosin ATPase located nearby on
      both sides of the M-band.
suggested_questions:
- question: Beyond the sarcomeric M-band, how much of cellular CK-MM function depends on
    its association with sarcoplasmic reticulum and sarcolemmal/T-tubule membranes for
    local ATP/ADP regulation of ion pumps?
suggested_experiments:
- hypothesis: M-band binding of CK-MM, mediated by the four M-specific N-terminal lysines
    (K8, K24, K104, K115), is required for efficient ATP regeneration at the myofibril
    rather than for catalysis per se.
  description: >-
    Express wild-type CKM and an M-band-binding-deficient lysine mutant (K8/K24/K104/K115)
    in muscle cells or Ckm-null myofibers, confirm equal intrinsic creatine kinase
    activity in vitro, then compare M-band localization (immuno-EM), contractile
    ATP/ADP buffering, and fatigue resistance during burst activity.
  experiment_type: structure-function / localization

CKM

Gene Description