| Domain/Motif | Location | Function | Key Features |
|---|---|---|---|
| N-terminal catalytic domain | N-terminal region of mature AprA | Catalyzes proteolytic cleavage of host and microbial substrates as a Zn²⁺-dependent metalloprotease | Contains the conserved HEXXHXXGXXH zinc-binding motif characteristic of serralysin-type metalloproteases; the active-site Zn²⁺ is essential for catalysis; responsible for cleavage of substrates such as complement proteins and ENaC (pqac-00000004, pqac-00000018) |
| C-terminal calcium-binding RTX domain | C-terminal region | Promotes folding, stabilization, and activation of the protease after Ca²⁺ binding | Contains RTX-associated Asp/Gly-rich nonapeptide repeats that form a Ca²⁺-bound parallel β-roll; intrinsically disordered or poorly folded without Ca²⁺; Ca²⁺ binding induces proper folding and enables full protease activity (pqac-00000002, pqac-00000018, pqac-00000019) |
| Metalloprotease superfamily classification | Whole protein / family-level annotation | Places AprA within the serralysin branch of secreted bacterial metalloproteases | AprA is a serralysin-family alkaline metalloprotease belonging to peptidase family M10B within the metzincin-like metalloprotease superfamily; this classification is consistent with the Zn²⁺ catalytic motif and Ca²⁺-regulated RTX architecture (pqac-00000000, pqac-00000004, pqac-00000018) |
| AprI inhibitor interaction | Functional interaction with AprA catalytic machinery | Protects the bacterium from uncontrolled AprA proteolysis and can block AprA activity extracellularly in vitro | AprI is the cognate alkaline protease inhibitor; it inhibits AprA near-stoichiometrically and blocks AprA-dependent ENaC activation; inhibitor action is linked to interaction with the Zn²⁺-containing protease active site, consistent with structural studies of the AprA-AprI system (pqac-00000002, pqac-00000006, pqac-00000019) |


*Table: This table summarizes the major structural and functional features of Pseudomonas aeruginosa AprA, including its catalytic and RTX calcium-binding regions, family classification, and interaction with the cognate inhibitor AprI. It is useful for connecting domain organization to secretion, activation, catalysis, and regulation.*