mucD (PA0766, G3XD20) notes

Identity

MucD (AlgY), HtrA/DegP-like serine protease (peptidase S1C, MEROPS S01.453), 474
aa-class protein with a SignalP signal peptide (1-25), trypsin-like protease
domain with charge-relay residues 114/144/217 (PIRSR) and two PDZ domains.
Unreviewed TrEMBL entry; last gene of the algU-mucA-mucB-mucC-mucD operon.
No deep-research provider was available; notes are from cached publications
and PubMed searches.

Discovery: mucD encodes an HtrA homolog; inactivation causes mucoidy and
heat/H2O2 sensitivity
PMID:8550474.
PseudoCAP localisation seed (Hay et al. 2012, abstract only)
PMID:21713511.
A 2026 paper describes this evidence as affinity pull-downs
PMID:42766672.
AlgX-MucD complex purified from detergent-solubilised membranes
PMID:16376476.
This paper has no protease assay, so it is a weak reference for the ISS
serine-type endopeptidase row (the ISS itself rests on E. coli DegP).
Regulated intramembrane proteolysis: in a mucD mutant MucA is degraded through
MucP even without AlgW
PMID:21036998.
This is a genetic (mutant + reporter + Western) paper, so IMP rather than IDA,
and it shows negative regulation of the AlgW/MucP signalling cascade, not a
part of it.
Direct biochemistry and structure (Jiang et al. 2026, full text): purified MucD
degrades AlgK and AlgX; S217A is inactive; cryo-EM of the 12-mer and
24-mer; resting 12-mer/active trimer equilibrium
PMID:42766672;
PMID:42766672;
P1 preference for small hydrophobic residues
PMID:42766672.

PTN node	node term	n_seeds	leaf IBAs	seed annotation (term, evidence, PMID)	verdict	rationale
PTN002342204	GO:0042597 periplasmic space	1 (sole seed)	5 (5 taxa)	GO:0042597 periplasmic space, IDA, PMID:21713511 (PseudoCAP)	SOUND	The abstract reports MucD in a periplasmic complex with AlgK and AlgX (affinity pull-downs). The paper is abstract-only here, so the exact fractionation could not be checked, but periplasmic location is independently supported by the SignalP signal peptide, the HtrA/DegP family, and the 2026 biochemical study, which treats MucD as periplasmic. The leaves (P. aeruginosa MucD, Neisseria HtrA Q4W577, Geobacter DegP Q74GB5, Bradyrhizobium Q89G41, Xanthomonas MucD Q8PB56) are all DegP-like proteases, for which periplasm is the standard location. The node term suits the clade.

GO:0007165 signal transduction IDA PMID:21036998: the paper is genetic and shows
that MucD negatively regulates MucA proteolysis. MODIFY to GO:0009968 negative
regulation of signal transduction; PSEUDOCAP defect (term and evidence code).
GO:0004252 ISS PMID:16376476 (with E. coli DegP): claim is correct (now
directly shown in PMID:42766672), but the cited paper shows only an AlgX-MucD
complex.

ACCEPT: periplasmic space (IBA, IEA, IDA), serine-type endopeptidase activity
(IEA, ISS), proteolysis (IEA).
MODIFY: signal transduction (IDA) -> negative regulation of signal transduction.
PSEUDOCAP defect (PROBABLE) on the signal transduction row.