prepilinPilD

Prepilin peptidase PilD, also known simply as PilD, is a membrane-associated enzyme that plays a central role in the biogenesis of type IV pili in many Gram-negative bacteria. It acts on prepilin subunits, the precursor forms of pilin proteins, converting them into mature pilins ready for assembly into the pilus filament.

The enzyme exhibits dual catalytic activities within a single polypeptide. First, it functions as a prepilin peptidase, cleaving off the class III leader peptide from prepilins at a conserved cleavage site, typically producing a mature N-terminus that begins with a phenylalanine residue. Second, PilD carries out N-methylation of this mature N-terminus using S-adenosyl-L-methionine as the methyl donor. This combination of proteolytic processing and methylation is essential for proper pilus assembly and function.

PilD is generally an integral inner membrane protein with multiple transmembrane segments. Its active site is oriented to process substrates that are embedded in or associated with the inner membrane, placing the maturation of pilins within the context of the cytoplasmic membrane-associated assembly machinery. The mature pilins produced by PilD are then assembled into type IV pili by the pilus biogenesis apparatus, including proteins such as PilB, PilC, and PilQ, driving processes such as adhesion, twitching motility, biofilm formation, and DNA uptake in competent cells.

Genetically, pilD is conserved across many pilus-producing bacteria, though the exact substrate range and regulatory controls can vary. Disruption of PilD typically abolishes pilus formation and related phenotypes, underscoring its essential role in pilin maturation and pilus biogenesis.