acs (Escherichia coli K-12, P27550) — curation notes

Provenance note. No deep-research API keys are available in this container, so
just deep-research could not be run and no -deep-research-<provider>.md file exists
for this gene. The literature below was assembled by reading the cached publications in
publications/, by PubMed searches (PubMed MCP), and from the curated UniProt record
acs-uniprot.txt. This file is the research record for the review.

Curation context: this gene was reviewed for the CACAO
project, which audits GO annotations carrying assigned_by: CACAO. acs carries four
such rows (see "CACAO rows" below).

1. What Acs is

Acetyl-coenzyme A synthetase (acetate--CoA ligase, AMP-forming; EC 6.2.1.1), a 652-residue
cytoplasmic member of the ATP-dependent AMP-binding (ANL) enzyme superfamily. It ligates
acetate to CoA at the expense of ATP in two half reactions through a covalently bound
acetyl-adenylate intermediate:

"Catalyzes the conversion of acetate into acetyl-CoA (AcCoA), an essential intermediate
at the junction of anabolic and catabolic pathways" ... "In the first half reaction, Acs
combines acetate with ATP to form acetyl-adenylate (AcAMP) intermediate. In the second
half reaction, it can then transfer the acetyl group from AcAMP to the sulfhydryl group
of CoA, forming the product AcCoA"
[file:ECOLI/acs/acs-uniprot.txt, CC:FUNCTION]

Reaction: acetate + ATP + CoA = acetyl-CoA + AMP + diphosphate (Rhea:RHEA:23176),
Mg(2+)-dependent, pH optimum 8.5, KM 0.2 mM acetate / 0.2 mM CoA / 0.15 mM ATP
[file:ECOLI/acs/acs-uniprot.txt, CC:CATALYTIC ACTIVITY, CC:COFACTOR,
CC:BIOPHYSICOCHEMICAL PROPERTIES].

The original enzymological identification of this activity in E. coli is Brown,
Jones-Mortimer & Kornberg: PMID:21941.

2. Gene identification and the acetate-activation role (PMID:7751300)

Kumari et al. cloned the ORF, deleted it, and purified the product:

PMID:7751300
PMID:7751300 — the IDA basis for
GO:0003987 acetyl-CoA synthetase activity.
PMID:7751300 (≤10 mM
acetate) and PMID:7751300 — the IMP basis for GO:0045733 acetate catabolic process.

Acs is the high-affinity (low-acetate) arm of acetate activation; AckA–Pta is the
low-affinity (high-acetate) arm. UniProt's disruption phenotype records the same split
[file:ECOLI/acs/acs-uniprot.txt, CC:DISRUPTION PHENOTYPE]. Acs is therefore a genuine
participant in acetate catabolism — it performs the committed activation step — which is
not the "downstream consequence of a knockout" pattern.

Transcriptionally Acs is induced by CRP and FNR in response to rising cAMP, falling
oxygen and changes in carbon flux [file:ECOLI/acs/acs-uniprot.txt, CC:INDUCTION;
PMID:10894724].

3. Second substrate: propionate

E. coli Acs also activates propionate, and is required for growth on it:

Together with the EcoCyc IDA row on GO:0050218 propionate-CoA ligase activity from the
purified-enzyme characterization PMID:15327942, this makes short-chain (C2/C3) acyl-CoA ligase
activity a real, second catalytic capability rather than a stray in-vitro promiscuity.

4. Acs is a substrate of protein acetylation, and is regulated by it

This is the best-documented protein-acetylation link for Acs, and it runs the opposite
way from the CACAO rows:

Acs Lys609 (the active-site lysine) is acetylated by the GNAT acetyltransferase
Pat/PatZ/YfiQ, which inactivates the enzyme: PMID:15236963 (Salmonella; the
E. coli orthologue PatZ is structurally characterized in PMID:40498448).
The sirtuin CobB deacetylates Lys609 and thereby activates Acs; Acs and CobB form a
1:1 complex [file:ECOLI/acs/acs-uniprot.txt, CC:PTM, CC:SUBUNIT; PMID:15019790;
PMID:20345663].

So in the Pat/CobB axis Acs is the modified protein, not the modifier.

5. The CheY-acetylation claim, and why it needs hedging

A single group (Eisenbach/Wolfe and co-workers) reported that Acs acetylates the
chemotaxis response regulator CheY:

PMID:1390767 — but note the paper's own
title attributes the chemistry to acetyladenylate or its derivative, i.e. to the
small-molecule intermediate Acs produces, not unambiguously to Acs as an enzyme.
PMID:15327942; PMID:15327942; PMID:15327942.
PMID:11359578 — the in-vivo chemotaxis phenotype.
PMID:16630631 — the reverse direction, used as the basis of the CACAO
protein lysine deacetylase activity row.

Three caveats, all from independent work:

The Δacs chemotaxis phenotype did not replicate. Li et al., testing the same
semi-solid-agar assay in W3110 and in the AJW613/AJW803 pair, found
PMID:20345663. They attribute the chemotaxis effect to CobB-mediated CheY
deacetylation instead. This directly disputes PMID:11359578 and the
phenotype sentence in PMID:16630631.
CheY is acetylated without Acs. PMID:16630631 — the same paper shows
CheY autoacetylates from AcCoA at a rate comparable to the Acs-mediated rate.
Most bacterial lysine acetylation is non-enzymatic. PMID:23830618, and global acetylation tracks
acetyl-phosphate levels rather than acetyltransferase activity. Since Acs makes
acetyl-adenylate and acetyl-CoA, an Acs-dependent increase in CheY acetylation can
arise from acyl-donor supply rather than from catalysis by Acs. The dedicated
E. coli protein acetyltransferase is PatZ, not Acs [PMID:15236963; PMID:40498448].

Mechanistic point relevant to the deacetylase term. GO:0033558 protein lysine deacetylase activity sits under GO:0019213 deacetylase activity, defined as
"Catalysis of the hydrolysis of an acetyl group from a substrate molecule" (OLS,
2026-10-29). Acs has no hydrolase chemistry: what PMID:15327942 and PMID:16630631
describe is the reverse of Acs's own acetyl-transfer reaction (acetyl group returned to
CoA/AMP), which is exactly what "reversible" means in the 2004 abstract. A reversible
transferase is annotated to the transferase term, not to a separate deacetylase term;
GO:0061733 protein-lysine-acetyltransferase activity is the term that covers both
directions of this one reaction.

6. Localization

Cytoplasmic/cytosolic. The IDA row rests on the E. coli cytosolic proteome
PMID:18304323; Acs itself is named only in that paper's supplementary
abundance table, not in the cached body text, so the row is accepted on EcoCyc's reading
of the supplementary data plus the absence of any TM segment, signal peptide or membrane
feature in acs-uniprot.txt.

7. CACAO rows (four)

GO term	Evidence	Reference	Verdict
GO:0003987 acetyl-CoA synthetase activity	IDA	PMID:7751300	correct and core (also carried by EcoCyc on the same paper)
GO:0018394 peptidyl-lysine acetylation	IDA	PMID:15327942	right paper, right assay, peripheral and donor-supply-confounded → keep as non-core
GO:0034421 post-translational protein acetylation	IDA	PMID:15327942	same single experiment annotated a second time on the timing axis; the residue-specific term is the informative one
GO:0033558 protein lysine deacetylase activity	IDA	PMID:16630631	claim is in the abstract, but the term's parent requires hydrolysis; this is reverse acetyl-transfer → acetyltransferase term

GONUTS wiki check: gowiki.tamu.edu was still serving only the "temporarily offline"
notice on 2026-10-29 (consistent with the note in projects/CACAO.md), so the students'
own evidence pages for PMID:15327942, PMID:16630631 and PMID:7751300 could not be read.
All four rows were judged from the papers and the surrounding literature. Re-check when
GONUTS returns.

8. Open questions

Is Acs a bona fide protein acetyltransferase, or does it raise CheY acetylation by
supplying acetyl-adenylate/acetyl-CoA for non-enzymatic modification? No experiment
separating catalysis from donor supply (e.g. a catalytically dead Acs variant that
still produces no AcAMP vs. one that does) has been reported.
Why do PMID:11359578 and PMID:20345663 disagree on the Δacs chemotaxis phenotype?
Does Acs contribute measurably to propionyl-CoA formation in vivo relative to PrpE,
and does Lys609 acetylation regulate both activities identically PMID:24835953?