Structure/Function Analysis of Neisseria meningitidis PilW, a Conserved Protein That Plays Multiple Roles in Type IV Pilus Biology

Type IV pili (Tfp) are widespread filamentous bacterial organelles that mediate multiple functions and play a key role in pathogenesis in several important human pathogens, including Neisseria meningitidis. Tfp biology remains poorly understood at a molecular level because the roles of the numerous proteins that are involved remain mostly obscure. Guided by the high-resolution crystal structure we recently reported for N. meningitidis PilW, a widely conserved protein essential for Tfp biogenesis, we have performed a structure/function analysis by targeting a series of key residues through site-directed mutagenesis and analyzing the corresponding variants using an array of phenotypic assays. Here we show that PilW’s involvement in the functionality of Tfp can be genetically uncoupled from its concurrent role in the assembly/stabilization of the secretin channels through which Tfp emerge on the bacterial surface. These findings suggest that PilW is a multifunctional protein. Throughout the bacterial kingdom, survival is linked to suc-cessful colonization of a niche favorable for bacterial growth. This is often mediated by adhesive, surface-exposed, hair-like filaments called pili or fimbriae (40). Of the several types of pili that have been identified so far, the most widespread are typ