Taurine / hypotaurine biosynthesis and transport (CDO1 -> CSAD / ADO; SLC6A6)

Taurine is one of the most abundant free amino acids in mammalian tissues, essential for bile-salt conjugation, osmoregulation, membrane stabilisation, calcium handling and mitochondrial tRNA modification; it is supplied both by endogenous biosynthesis from cysteine and by cellular uptake. The main biosynthetic route starts with cysteine dioxygenase (CDO1), which oxidises L-cysteine to 3-sulfino-L-alanine (cysteinesulfinate) using O2 and a non-heme Fe(II) centre — the committed, rate-limiting step of cysteine catabolism. Cysteinesulfinic acid decarboxylase (CSAD), a PLP-dependent enzyme, then decarboxylates cysteinesulfinate to hypotaurine. A parallel route is provided by 2-aminoethanethiol (cysteamine) dioxygenase (ADO), which oxidises cysteamine (derived from coenzyme A / pantetheine turnover) directly to hypotaurine; ADO is additionally the N-terminal cysteine dioxygenase of the Cys/N-degron oxygen-sensing pathway. Hypotaurine from either route is oxidised to taurine. Cells that synthesise little taurine rely on the plasma-membrane Na+/Cl- -coupled taurine transporter SLC6A6 (TauT) to import it. Defects illustrate the pathway's importance: SLC6A6 loss-of-function causes taurine-deficiency retinal degeneration and cardiomyopathy, and CDO1 is frequently epigenetically silenced in cancer.

MODULE:taurine_biosynthesis_and_transportDRAFTMetabolic Pathwaymodules/taurine_biosynthesis_and_transport.yaml
taurine biosynthetic processGO:0042412 sulfur amino acid catabolic processGO:0000098 taurine transmembrane transportGO:0015734
GO:0042412
taurine biosynthetic process
CDO1/CSAD and ADO synthesise hypotaurine/taurine from cysteine and cysteamine (GO:0042412).
GO:0000098
sulfur amino acid catabolic process
The CDO1 step initiates catabolism of the sulfur amino acid cysteine (GO:0000098).
GO:0015734
taurine transmembrane transport
SLC6A6 imports taurine across the plasma membrane (GO:0015734).
file:human/CDO1/CDO1-ai-review.yaml
CDO1 gene review (human)
Cysteine dioxygenase (UniProtKB:Q16878, GO:0017172) matches the completed human CDO1 review.
file:human/CSAD/CSAD-ai-review.yaml
CSAD gene review (human)
Cysteinesulfinic acid decarboxylase (UniProtKB:Q9Y600, GO:0004782) matches the completed human CSAD review.
file:human/ADO/ADO-ai-review.yaml
ADO gene review (human)
Cysteamine dioxygenase / N-terminal cysteine dioxygenase (UniProtKB:Q96SZ5, GO:0047800) matches the completed human ADO review.
file:human/SLC6A6/SLC6A6-ai-review.yaml
SLC6A6 gene review (human)
Taurine:sodium symporter / TauT (UniProtKB:P31641, GO:0005369) matches the completed human SLC6A6 review.
5Nodes
4Parts
0Variant Sets
0Variants
4Annotons
3Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:taurine_biosynthesis_and_transport deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Reaction chaining (advisory)

✓ every PRECEDES step chains, or its break is acknowledged via chaining_status.

  • cysteinesulfinate_decarboxylation → taurine_transport [NOT_CHECKED]
  • cysteamine_dioxygenation → taurine_transport [NOT_CHECKED]

Function consistency and core coverage

4 gene-function check(s) reflected in core functions · 0 conflict(s) · 4 evidence or coverage gap(s) (8 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
cdo1_activity CDO1 (human)
UniProtKB:Q16878
Family Representative 		cysteine dioxygenase activity
GO:0017172 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
csad_activity CSAD (human)
UniProtKB:Q9Y600
Family Representative 		sulfinoalanine decarboxylase activity
GO:0004782 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ado_activity ADO (human)
UniProtKB:Q96SZ5
Family Representative 		cysteamine dioxygenase activity
GO:0047800 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
slc6a6_activity SLC6A6 / TauT (human)
UniProtKB:P31641
Family Representative 		taurine:sodium symporter activity
GO:0005369 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cdo1_activity CDO1 / cysteine dioxygenase family
PANTHER:PTHR12918
Family 		cysteine dioxygenase activity
GO:0017172 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR12918.
csad_activity CSAD / glutamate-decarboxylase-like (group II PLP decarboxylase) family
PANTHER:PTHR45677
Family 		sulfinoalanine decarboxylase activity
GO:0004782 		Family Scope Restricted
GO:0004782 is SUBFAMILY_ONLY; this family grounding does not establish the allowed subfamily scope. Asserted by taurine_biosynthesis_and_transport; accepted by CSAD.
ado_activity ADO / cysteamine (thiol) dioxygenase family
PANTHER:PTHR22966
Family 		cysteamine dioxygenase activity
GO:0047800 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR22966.
slc6a6_activity SLC6 Na+/Cl- -dependent neurotransmitter transporter family
PANTHER:PTHR11616
Family 		taurine:sodium symporter activity
GO:0005369 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR11616.

Gene-review completeness (4/4 grounded genes reviewed)

4 complete review(s) · 0 with deep research · 0 missing review · 4 reviewed but lacking deep research

Gene Review Complete Deep research
ADO Q96SZ5 ✓ ✓ ✗
CDO1 Q16878 ✓ ✓ ✗
CSAD Q9Y600 ✓ ✓ ✗
SLC6A6 P31641 ✓ ✓ ✗

Details

Context
cytosolGO:0005829 plasma membraneGO:0005886
Taurine / hypotaurine biosynthesis and transportMetabolic Pathwaytaurine_biosynthesis_and_transport
taurine biosynthetic processGO:0042412 sulfur amino acid catabolic processGO:0000098 taurine transmembrane transportGO:0015734
Context
cytosolGO:0005829 plasma membraneGO:0005886

Taurine / hypotaurine biosynthesis and transport (GO:0042412 + GO:0015734), grounded to four completed human gene reviews. Two biosynthetic routes converge on hypotaurine: (route 1) CDO1 (Q16878 PTHR12918, GO:0017172, non-heme Fe(II), Cys-Tyr cofactor) oxidises L-cysteine -> cysteinesulfinate, then CSAD (Q9Y600 PTHR45677, GO:0004782, PLP) decarboxylates it -> hypotaurine; (route 2) ADO (Q96SZ5 PTHR22966, GO:0047800, non-heme Fe(II)) oxidises cysteamine -> hypotaurine. Hypotaurine is then oxidised to taurine (the terminal oxidation lacks a firmly assigned human enzyme, so it is not modelled as a node). SLC6A6 (P31641 PTHR11616, GO:0005369, Na+/Cl- symport) imports taurine at the plasma membrane, dominating supply in low-synthesis tissues (retina, heart). ADO is dual-function: besides cysteamine dioxygenase it is the Cys/N-degron N-terminal cysteine dioxygenase oxygen sensor (peptidyl-cysteine oxidation; a proposed_new_ term for the protein-N-terminal-cysteine-dioxygenase MF was noted in the ADO review, since GO lacks a dedicated class). CDO1 is a frequently-silenced tumour suppressor; SLC6A6 LOF -> taurine-deficiency retinal degeneration/cardiomyopathy. GO term ids/labels verified against the local go.db; module passes structural + term-label validation.

Connections

CDO1-made cysteinesulfinate is decarboxylated by CSAD to hypotaurine.
Hypotaurine (from CSAD or ADO) is oxidised to taurine, whose cellular pool SLC6A6 also replenishes by uptake.
Hypotaurine from the ADO route likewise feeds the taurine pool that SLC6A6 imports.
Part 1: cysteine dioxygenation (cysteine -> cysteinesulfinate)
Cysteine dioxygenase (CDO1)Reactioncysteine_dioxygenation

Annotons

CDO1: cysteine dioxygenase
cdo1_activity
Participant: Family: CDO1 / cysteine dioxygenase family
Family:
CDO1 / cysteine dioxygenase familyPANTHER:PTHR12918
Representative Members: CDO1 (human)UniProtKB:Q16878

Function

cysteine dioxygenase activityGO:0017172
Substrates: L-cysteine O2 (non-heme Fe2+)
Products: 3-sulfino-L-alanine (L-cysteinesulfinate)

Locations

cytosolGO:0005829

Oxidise L-cysteine to cysteinesulfinate.

Part 2: cysteinesulfinate decarboxylation (-> hypotaurine)
Cysteinesulfinic acid decarboxylase (CSAD)Reactioncysteinesulfinate_decarboxylation

Annotons

CSAD: sulfinoalanine decarboxylase
csad_activity
Participant: Family: CSAD / glutamate-decarboxylase-like (group II PLP decarboxylase) family
Family:
CSAD / glutamate-decarboxylase-like (group II PLP decarboxylase) familyPANTHER:PTHR45677
Representative Members: CSAD (human)UniProtKB:Q9Y600

Function

sulfinoalanine decarboxylase activityGO:0004782
Substrates: 3-sulfino-L-alanine (L-cysteinesulfinate; PLP)
Products: hypotaurine CO2

Locations

cytosolGO:0005829

Decarboxylate cysteinesulfinate to hypotaurine.

Part 3: cysteamine dioxygenation (parallel hypotaurine route)
Cysteamine (2-aminoethanethiol) dioxygenase (ADO)Reactioncysteamine_dioxygenation

Annotons

ADO: cysteamine dioxygenase
ado_activity
Participant: Family: ADO / cysteamine (thiol) dioxygenase family
Family:
ADO / cysteamine (thiol) dioxygenase familyPANTHER:PTHR22966
Representative Members: ADO (human)UniProtKB:Q96SZ5

Function

cysteamine dioxygenase activityGO:0047800
Substrates: cysteamine (2-aminoethanethiol) O2 (non-heme Fe2+)
Products: hypotaurine

Locations

cytosolGO:0005829

Oxidise cysteamine to hypotaurine (alternative route).

Part 4: cellular taurine uptake
Taurine transporter TauT (SLC6A6)Reactiontaurine_transport

Annotons

SLC6A6: taurine:sodium symporter (TauT)
slc6a6_activity
Participant: Family: SLC6 Na+/Cl- -dependent neurotransmitter transporter family
Family:
SLC6 Na+/Cl- -dependent neurotransmitter transporter familyPANTHER:PTHR11616
Representative Members: SLC6A6 / TauT (human)UniProtKB:P31641

Function

taurine:sodium symporter activityGO:0005369
Substrates: taurine (extracellular; Na+ / Cl- coupled)
Products: taurine (cytosolic)

Locations

plasma membraneGO:0005886

Import extracellular taurine into the cytosol (Na+/Cl- symport).