ARG1 (Arginase-1, human, UniProtKB:P05089) — review notes

Summary of function

ARG1 is the cytosolic, liver-type (type I) arginase, a binuclear manganese
metalloenzyme that catalyzes the terminal (fifth) step of the urea cycle:
L-arginine + H2O -> L-ornithine + urea (EC 3.5.3.1). It regenerates ornithine to
close the cycle and produces the urea that is excreted. It is a homotrimer, each
subunit binding two Mn(2+) ions. Beyond hepatic ureagenesis, ARG1 is
constitutively expressed in neutrophil granules and released during inflammation,
where local arginine depletion suppresses T-cell (and NK-cell) proliferation /
cytokine production — a myeloid immunoregulatory role. Loss-of-function variants
cause argininemia / arginase deficiency, a urea cycle disorder distinguished by
progressive spastic diplegia/paraparesis rather than the neonatal hyperammonemic
crises typical of proximal UCDs.

Key verbatim citations

• Terminal urea-cycle step + disease:
  PMID:3540966

• Catalytic activity / Mn metalloenzyme:
  PMID:17562323
  PMID:21728378
  PMID:21728378

• Binuclear Mn cluster / structure:
  PMID:16141327

• Homotrimer / quaternary structure:
  PMID:22959135

• Neutrophil/granulocyte expression + azurophil granule + antimicrobial:
  PMID:15546957
  PMID:15546957

• T-cell suppression via extracellular arginase / arginine depletion:
  PMID:16709924

• CMTM6 interaction (ARG1 identified as MS interactor in a PD-L1/CMTM6 study; ARG1 itself not the paper's focus):
  UniProt: "INTERACTION WITH CMTM6, AND IDENTIFICATION BY MASS SPECTROMETRY" (RN[15], PMID:28813417).
  Paper abstract is about CMTM6 regulating PD-L1; ARG1 is one MS-detected CMTM6 co-precipitant.

• Sperm nucleus proteomics (HDA nucleus): PMID:21630459 is a bulk sperm-nuclear
  proteome catalog (403 proteins); ARG1 detection is a large-scale MS hit, not a
  dedicated study of nuclear ARG1 function.

Disease (dismech Arginase_Deficiency.yaml)

"progressive spastic diplegia or paraparesis, seizures, intellectual disability,
and growth retardation... relatively infrequent hyperammonemia compared to other
urea cycle disorders." Neurotoxicity from arginine + guanidino compounds.

GO term-definition checks (OLS)

• GO:0004053 arginase activity = "L-arginine + H2O = L-ornithine + urea" (exact MF). CORE.
• GO:0000050 urea cycle = full cycle; ARG1 does terminal step. CORE BP.
• GO:0016813 hydrolase acting on C-N linear amidines = PARENT of arginase activity
  (InterPro Mn-binding-site IEA); redundant/over-general vs GO:0004053 -> MODIFY.
• GO:0046872 metal ion binding = PARENT of GO:0030145 manganese ion binding;
  general -> MODIFY to GO:0030145 (which is verified, binuclear Mn cluster).
• GO:0006527 L-arginine catabolic process = verified BP (breakdown of L-arginine). ACCEPT.
• GO:0006525 arginine metabolic process = broader parent; keep (IBA/IEA).
• GO:0030145 manganese ion binding = binds 2 Mn2+/subunit. CORE MF (contributes_to).
• GO:0005829 cytosol = verified subcellular localization (arginase I cytosolic). CORE CC.
• GO:0005737 cytoplasm = parent of cytosol; keep.
• GO:0005576 extracellular region (IDA PMID:16709924) = neutrophil arginase released
  extracellularly; real but non-core (secondary immune role).
• GO:0035578 azurophil granule lumen / GO:0035580 specific granule lumen (Reactome
  neutrophil degranulation) = real neutrophil granule localization; non-core.
• GO:0005634 nucleus (HDA PMID:21630459) = bulk sperm-nucleus proteomics; likely
  not a functional nuclear localization -> non-core / over-annotated.
• GO:0070947 neutrophil-mediated killing of fungus (IMP PMID:15546957) = supported
  by fungicidal-activity paper; non-core immune role.
• GO:0042130 neg reg T cell proliferation (IDA/IBA PMID:16709924) = supported; non-core.
• GO:0060336 neg reg type II IFN signaling (IMP PMID:16709924) = downstream immune
  effect; keep as non-core.
• GO:0042832 defense response to protozoan / GO:0046007 neg reg activated T cell
  proliferation / GO:2000552 neg reg Th2 cytokine production (Ensembl GO_REF:0000107
  IEA from mouse Q61176) = orthology-transferred mouse immune roles; keep non-core.
• GO:0042127 regulation of cell population proliferation (ARBA IEA) = very general;
  over-annotated relative to the specific T-cell terms -> MARK_AS_OVER_ANNOTATED.
• GO:0005515 protein binding (IPI CMTM6, PMID:28813417) = uninformative; MS
  interactor from a PD-L1 study -> non-informative binding, mark over-annotated.

Deep research

falcon deep-research launched (just deep-research-falcon human P05089 --alias ARG1);
FAILED after 600s ("All providers failed" — falcon endpoint timeout). No
-deep-research-falcon.md file produced. Review grounded in the UniProt record, all 9
cached publications, and dismech Arginase_Deficiency.yaml. No DR file fabricated.