GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

Keywords for Aminopeptidase, Hydrolase, Metal-binding, Metalloprotease, and Protease were correctly used to infer GO annotations for molecular function.

PMID:23226342

Functional characterization of two M42 aminopeptidases erroneously annotated as cellulases.

CelM from Clostridium thermocellum was experimentally characterized as an M42 family aminopeptidase, not a cellulase as previously annotated.

"some members have been annotated as cellulases because of their homology with CelM, formerly described as an endoglucanase of Clostridium thermocellum"
The protein shows no significant cellulase activity on CMC and cellobiose.

"No significant endoglucanase activity was measured, either for TmPep1050 or CelM"
CelM has robust leucine aminopeptidase activity with L-leucine-pNA as the optimal substrate.

"Both enzymes were shown to catalyze hydrolysis of nonpolar aliphatic L-amino acid-pNA substrates, the L-leucine derivative appearing as the best substrate"
Cobalt ions (Co2+) are required for maximal activity.

"Addition of cobalt ions enhanced the activity of both enzymes significantly"
EDTA inhibits activity, confirming metal-dependence.

"both the chelating agent EDTA and bestatin, a specific inhibitor of metalloaminopeptidases, proved inhibitory"
Bestatin inhibits CelM, consistent with metalloaminopeptidase function.

"bestatin, a specific inhibitor of metalloaminopeptidases, proved inhibitory"

UniProt:P55742

UniProt entry for CelM/Putative aminopeptidase

Classified as Peptidase M42 family member.

"Belongs to the peptidase M42 family."
Binds 2 divalent metal cations per subunit.

"Binds 2 divalent metal cations per subunit."

PMID:26546839

TET peptidases: A family of tetrahedral complexes conserved in prokaryotes.

M42/TET peptidases are ATP-independent cytosolic prokaryotic peptidases that assemble into 12-subunit hollow tetrahedral dodecamers and act as non-processive cobalt-activated aminopeptidases.
Activity toward polypeptides is coupled to assembly; the dodecamer creates a protected internal compartment, while dimers are markedly less active especially on larger substrates.

PMID:29866801

Characterization of a Glycyl-Specific TET Aminopeptidase Complex from Pyrococcus horikoshii.

TET aminopeptidase complexes exhibit varied substrate preferences across the family (e.g., glycyl-specific, lysyl-specific, leucyl-like), supporting paralog diversification within the M42/TET family.

PMID:35395851

Functional control of a 0.5 MDa TET aminopeptidase by a flexible loop revealed by MAS NMR.

A loop within the catalytic chamber of TET2 stabilizes substrates and activates the catalytic water (a conserved histidine plays a key role); provides modern mechanistic context for the M42/TET family that includes CelM.

file:ACET2/P55742/P55742-deep-research-falcon.md

Deep research report on celM/P55742 (Falcon/Edison Scientific Literature)

CelM is an M42-family aminopeptidase (not a cellulase) forming an active dodecameric TET complex; misannotation as cellulase stems from the cel-prefix nomenclature, and direct biochemical assays show no detectable activity on cellobiose, CMC, or filter paper cellulose.
Quantitative kinetic constants for CelM include kcat/Km = 114.3 s^-1 M^-1 (Leu-pNA), 39.3 (Ile-pNA), 24.8 (Met-pNA); cobalt-activated specific activity rises from 3.8 (no metal) to 319.6 mmol min^-1 mmol^-1 enzyme at 100 uM Co2+; bestatin Ki approximately 292 nM; activation energy 60.5 kJ/mol.
Dodecameric assembly is required for full activity (291.7 mmol min^-1 mmol^-1 vs 6.4 for the dimer), aligning CelM with the broader TET self-compartmentalized paradigm.
CelM lacks a dockerin domain and is not a cellulosome component; localization is inferred cytosolic based on M42/TET family precedent since no direct localization assay for the A. thermocellus enzyme has been reported.