Pili with strong attachments: Gram‐positive bacteria do it differently

Abstract

SummaryBacteria attach to their appropriate environmental niche by using adhesins. To maximize their contact with the environment, adhesins are often present on the ends of long hairlike structures called pili. Recently, attention has focused on pili of Grampositive bacteria because they may be vaccine candidates in important human pathogens. These pili differ from the well-studied pili of Gram-negative bacteria because their subunits are covalently linked, they do not require specific chaperones for assembly, and the tip protein (likely to be the adhesin) is not required to initiate formation of the pilus structure. In Gram-positive bacteria, the genes for pili occur in clusters, which may constitute mobile genetic elements. These clusters include the transpeptidase(s) of the sortase family that is/are required for polymerization of the subunit proteins. However, efficient covalent attachment of the completed pilus structure to the cell wall is accomplished, in cases where this has been studied, by the 'housekeeping' sortase, which is responsible for attachment to the peptidoglycan of most surface proteins containing cell wall sorting signals. This enzyme is encoded elsewhere on the genome. Because pili of Grampositive bacteria have not been extensively investigated yet, we hope that this MicroReview will help to pinpoint the areas most in need of further study.

Functional Analysis of Lactobacillus rhamnosus GG Pili in Relation to Adhesion and Immunomodulatory Interactions with Intestinal Epithelial Cells

“…Unlike the pilus-like appendages in Gram-negative bacteria, Gram-positive pili represent a polymerized assemblage of different protein subunits (called pilins), which are covalently linked by the transpeptidase action of sortase enzymes. There is only a limited understanding about the biological role of the Gram-positive pilus, although reports in pathogens are steadily increasing (28,32,35,37). Recently, we documented for the first time that surface piliation is associated with the probiotic L. rhamnosus GG (19,26).…”

Role of MshQ in MSHA pili biosynthesis and biofilm formation of Aeromonas hydrophila

“…MSHA is a member of the family of type IV pili, which had been suggested to be involved in attachment to the abiotic surface and is required for adhesion and biofilm formation in other bacteria (Watnich and Kolter, 1999;Hadi et al, 2012). Unlike other bacterial pili, which use as few as 2 proteins for assembly, type IV pilus biogenesis requires a dozen or more proteins (Scott and Zahner, 2006). Genetic and transcriptional analyses of the MSHA type IV pilus gene locus of the V. cholerae O1 EI Tor biotype revealed that 16 ORFs were required for MASH pilus biogenesis, these ORFs were designated mshA to mshQ (Marsh and Taylor, 1999).…”

Type IV pili: paradoxes in form and function

“…Beneath their plain façade lies an exquisite helical architecture that provides for strength, flexibility and a multitude of functions, including twitching and gliding motility, adhesion, immune escape, DNA uptake, biofilm formation, microcolony formation, secretion, phage transduction and signal transduction. Unlike other bacterial pili, which use as few as two proteins for assembly [1,2], Type IV pilus biogenesis requires a dozen or more proteins, many of which share sequence conservation among divergent species. Pili are assembled, and in some cases disassembled, rapidly using powerful molecular motors that hydrolyze ATP.…”