PP_2638

Summary: Outer membrane is the appropriate location for the BcsC-like PP_2638 cellulose synthase operon C protein.

Reason: The target contains a BcsC C-terminal barrel-domain signature preceded by TPR repeats. The E. coli BcsC structure directly places the homologous 16-stranded barrel in the outer membrane. Together these support the outer-membrane assignment for KT2440, independently of its submitted protein name or the annotation under review.

Summary: Refine the supported cellulose-producing role to bacterial cellulose biosynthesis.

Reason: PP_2638 carries the BcsC C-terminal domain (Pfam PF05420 BCSC_C, residues 806-1152) preceded by TPR repeats, the architecture of the BcsC cellulose-export porin. Its role in cellulose production is argued from that family membership; the evidence is for characterized BcsC orthologs (E. coli/Enterobacteriaceae), where BcsC is essential in vivo for cellulose secretion and forms the outer-membrane channel of the Bcs synthase-secretion complex, not a KT2440 assay. BcsC contributes the export step of cellulose production rather than glucan polymerization (done by BcsA). The UniProt FUNCTION and PATHWAY lines are ARBA predictions and are not cited. GO:0090540 is the supported is_a descendant: its added distinction is bacterial context, not a different polymer or a stronger native-output claim. The inferred participation is cellulose export through a bacterial BcsC-family channel, not polymerization or a direct KT2440 secretion assay.

Proposed replacements: bacterial cellulose biosynthetic process

Summary: BcsC-family architecture supports the missing polysaccharide export activity.

Reason: The target combines the BcsC-specific C-terminal barrel domain with a TPR-rich periplasmic region. E. coli structures and functional work identify BcsC as the cellulose outer-membrane conduit; transfer therefore supports polysaccharide transmembrane transporter activity for PP_2638. This is a homolog-based assignment, not direct KT2440 transport. GO:0015288 porin activity is unsuitable because its current definition restricts transported substances to less than 1000 Da; cellulose is a polymer. No ATP-coupled transport mechanism or phosphoethanolamine modification is inferred.