CKMT1A encodes the ubiquitous mitochondrial creatine kinase (U-MtCK / Mia-CK), a member of the ATP:guanido phosphotransferase (phosphagen kinase) family that reversibly catalyzes phosphoryl transfer between ATP and creatine (creatine + ATP = N-phosphocreatine + ADP + H+; EC 2.7.3.2). The protein is synthesized with an N-terminal mitochondrial transit peptide and, after import, assembles into homo-octamers (four homodimers) that reside in the mitochondrial intermembrane space as peripheral membrane proteins on the intermembrane (outer) face of the inner membrane. Octamers bind the inner-membrane phospholipid cardiolipin via an N-terminal region, can bridge the inner and outer membranes at contact sites, and are functionally coupled to the adenine nucleotide translocator and to porin/VDAC. Using ATP exported from oxidative phosphorylation, the enzyme loads high-energy phosphate onto creatine to make phosphocreatine, constituting the mitochondrial (phosphate-loading) limb of the phosphocreatine shuttle that buffers cytosolic ATP at sites of high, fluctuating energy demand such as heart, skeletal muscle and brain. Mitochondrial creatine kinase octamers also contribute to mitochondrial structure and to regulation of the mitochondrial permeability transition. In humans the protein is encoded by two near-identical duplicated genes, CKMT1A and CKMT1B, both represented by UniProt entry P12532; it is distinct from the muscle-restricted sarcomeric mitochondrial creatine kinase (CKMT2) and from the cytosolic isoenzymes (CKM, CKB).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004111 creatine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetically inferred creatine kinase activity. This is the precise, correct molecular function of CKMT1A and is the core enzymatic activity of the protein, consistent with the EC 2.7.3.2 assignment and the crystal/cryo-EM structures. Reason: Creatine kinase activity is the defining, experimentally and structurally supported function of the mitochondrial creatine kinase family; this is a core function. Supporting Evidence: PMID:2914937 Creatine kinase (CK; EC 2.7.3.2) isoenzymes play prominent roles in energy metabolism. |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetically inferred mitochondrial localization. Correct but non-specific; the protein is more precisely localized to the mitochondrial intermembrane space / intermembrane face of the inner membrane. Reason: Accurate but superseded by the more specific intermembrane-space / inner-membrane location captured in core_functions; retained as a true but coarse statement. |
| GO:0046314 phosphocreatine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetically inferred involvement in phosphocreatine biosynthesis. This is the direct biological process carried out by the creatine kinase reaction (forming N-phosphocreatine) and is a core process for the mitochondrial enzyme, which supplies the phosphate-loading limb of the phosphocreatine shuttle. Reason: The creatine kinase reaction produces phosphocreatine; this process annotation is directly entailed by the molecular function and is core. Supporting Evidence: PMID:2914937 support the phosphocreatine shuttle hypothesis |
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Root-level catalytic activity term from InterPro2GO. Correct but maximally generic; the specific creatine kinase activity (GO:0004111) is already annotated. Reason: Uninformative parent of the specific GO:0004111 already present; adds no curation value. |
| GO:0004111 creatine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Creatine kinase activity inferred electronically from the EC 2.7.3.2 / RHEA:17157 mapping. Same correct molecular function as the IBA and TAS annotations of this term. Reason: Correct specific molecular function, redundant with but consistent with the IBA/TAS creatine kinase activity annotations; core. |
| GO:0005743 mitochondrial inner membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Electronically inferred inner-membrane localization from the UniProt subcellular-location keyword. Consistent with experimental evidence: the octamer is a peripheral membrane protein on the intermembrane (outer) face of the inner membrane and binds cardiolipin. Reason: Matches the curated UniProt subcellular location (Mitochondrion inner membrane; peripheral; intermembrane side); correct compartment. |
| GO:0016301 kinase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic kinase activity from InterPro2GO. Correct but a non-specific parent of creatine kinase activity (GO:0004111). Reason: Subsumed by the specific GO:0004111 already annotated; over-general. |
| GO:0016772 transferase activity, transferring phosphorus-containing groups | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic phosphotransferase grouping term from InterPro2GO. Correct but a high-level parent of the specific creatine kinase activity. Reason: Non-specific ancestor of GO:0004111; adds no value beyond the specific term. |
| GO:0016775 phosphotransferase activity, nitrogenous group as acceptor | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Phosphotransferase with a nitrogenous (guanidino) acceptor — the family-level activity captured by InterPro2GO. Accurate (creatine is the nitrogenous acceptor) but still a parent of the specific GO:0004111. Reason: Correct but subsumed by the specific creatine kinase activity already annotated. |
| GO:0046314 phosphocreatine biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: Phosphocreatine biosynthetic process inferred electronically from InterPro. Same correct core process as the IBA annotation of this term. Reason: Correct biological process directly entailed by creatine kinase activity; core, consistent with the IBA annotation. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | KEEP AS NON CORE | Summary: Bare protein-binding annotation from a high-throughput binary interactome map (HuRI). Not informative about molecular function; the relevant binding partners are better captured as specific interactions rather than as a generic MF term. Reason: Per curation guidelines, bare 'protein binding' is uninformative as a molecular function and is not a core function; the underlying high-throughput interaction is retained but non-core. |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | KEEP AS NON CORE | Summary: Bare protein-binding annotation from a neurodegeneration interactome-mapping study. Uninformative as a molecular function. Reason: Generic 'protein binding' from a high-throughput screen; not a core molecular function. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | KEEP AS NON CORE | Summary: Bare protein-binding annotation from a proteome-scale AP-MS network (BioPlex). Uninformative as a molecular function. Reason: Generic 'protein binding' from a high-throughput screen; not a core molecular function. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | KEEP AS NON CORE | Summary: Bare protein-binding annotation from a multimodal cell-mapping study. Uninformative as a molecular function. Reason: Generic 'protein binding' from a high-throughput screen; not a core molecular function. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | KEEP AS NON CORE | Summary: High-throughput proteomic detection of the protein in mitochondria. Correct compartment but non-specific relative to the intermembrane-space / inner-membrane location. Reason: Accurate but coarse; the specific location is captured in core_functions. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-200326 | ACCEPT | Summary: Reactome-asserted inner-membrane localization for the creatine kinase octamer reaction. Consistent with the peripheral, intermembrane-side inner-membrane localization of U-MtCK. Reason: Matches curated localization (intermembrane face of the inner membrane); correct compartment. |
| GO:0004111 creatine kinase activity | TAS PMID:2914937 Isolation and characterization of the gene and cDNA encoding... | ACCEPT | Summary: Author-asserted creatine kinase activity from the paper that isolated the human mitochondrial CK gene/cDNA. This is the core, correct molecular function. Reason: Traceable author statement of the defining enzymatic activity (EC 2.7.3.2); core. Supporting Evidence: PMID:2914937 Creatine kinase (CK; EC 2.7.3.2) isoenzymes play prominent roles in energy metabolism. |
| GO:0005739 mitochondrion | TAS PMID:2914937 Isolation and characterization of the gene and cDNA encoding... | KEEP AS NON CORE | Summary: Author-asserted mitochondrial localization. Correct but non-specific; the precise location is the intermembrane space / intermembrane face of the inner membrane. Reason: Accurate but coarse compartment; the specific localization is captured in core_functions. |
| GO:0005758 mitochondrial intermembrane space | IC UniProtKB:P12532 | NEW | Summary: The catalytically active CKMT1A octamer is a peripheral inner-membrane protein on the intermembrane side, i.e. it faces the mitochondrial intermembrane space. This is the precise compartment for its function and is proposed as a more specific localization than mitochondrion/inner membrane. GO:0005758 was not present in GOA; added here for consistency with the parallel CKMT2 review and with this review's core_functions. Reason: More specific localization for the active octamer, inferred from the curated UniProt subcellular location (inner membrane, peripheral, intermembrane side). Supporting Evidence: UniProtKB:P12532 Mitochondrion inner membrane; Peripheral membrane |
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Download this section (compressed HTML)Q: Is the regulation of the mitochondrial permeability transition by CKMT1 a direct structural/gating role of the octamer at contact sites, or an indirect consequence of altered local ATP/ADP and cardiolipin organization?
Q: Do CKMT1A and CKMT1B (the duplicated genes encoding identical protein) show any tissue- or context-specific differences in expression or regulation despite producing the same enzyme?
Experiment: Reconstitute purified CKMT1 octamers vs. dimer-stabilized mutants with cardiolipin-containing proteoliposomes containing ANT/VDAC and measure ATP/ADP channeling and phosphocreatine production relative to bulk substrate.
Hypothesis: Octamer formation and cardiolipin binding are required for functional coupling of CKMT1 to the adenine nucleotide translocator and for efficient phosphocreatine export.
Type: biochemical reconstitution
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