The major subunit of widespread competence pili exhibits a novel and conserved type IV pilin fold

Abstract

Type IV filaments (T4F), which are helical assemblies of type IV pilins, constitute a superfamily of filamentous nanomachines virtually ubiquitous in prokaryotes that mediate a wide variety of functions. The competence (Com) pilus is a widespread T4F, mediating DNA uptake (the first step in natural transformation) in bacteria with one membrane (monoderms), an important mechanism of horizontal gene transfer. Here, we report the results of genomic, phylogenetic, and structural analyses of ComGC, the major pilin subunit of Com pili. By performing a global comparative analysis, we show that Com pili genes are virtually ubiquitous in Bacilli, a major monoderm class of Firmicutes. This also revealed that ComGC displays extensive sequence conservation, defining a monophyletic group among type IV pilins. We further report ComGC solution structures from two naturally competent human pathogens, Streptococcus sanguinis (ComGCSS) and Streptococcus pneumoniae (ComGCSP), revealing that this pilin displays extensive structural conservation. Strikingly, ComGCSS and ComGCSP exhibit a novel type IV pilin fold that is purely helical. Results from homology modeling analyses suggest that the unusual structure of ComGC is compatible with helical filament assembly. Because ComGC displays such a widespread distribution, these results have implications for hundreds of monoderm species.

Mechanism of assembly of type 4 filaments: everything you always wanted to know (but were afraid to ask)

“…[127]; (2) major pilins from Com pili in Firmicutes that display a purely helical globular head [55]; or (3) modular minor pilins with a variety of protein domains grafted onto a pilin via short linkers [20,21].…”

“…ComGB from S. sanguinis has been chosen as an example [55], and exhibits a 89.08 % pLDDT. Left, structure in the context of the CM.…”

“…The C-terminal half of α1 (α1C) is packed against the globular head, which is often built around an antiparallel β-sheet. However, there are variations such as in (1) major pilins from Geobacter species, where the stick and globular head are two different proteins [127]; (2) major pilins from Com pili in Firmicutes that display a purely helical globular head [55]; or (3) modular minor pilins with a variety of protein domains grafted onto a pilin via short linkers [20, 21].…”

Manganese depletion leads to multisystem changes in the transcriptome of the opportunistic pathogenStreptococcus sanguinis

“…S6). S. sanguinis is unusual in that it is the only streptococcal species to encode a gene cluster for the biosynthesis of a type IV pilus system (T4P) (Gurung et al, 2016) that is distinct from the T4P competence pilus (Sheppard et al, 2020), and yet few strains exhibit the twitching motility normally mediated by T4P (Chen et al, 2019). In SK36, T4P appears to be important for adherence to host cells and may be regulated by CcpA, despite the lack of a cre site in the promoter region (Bai et al, 2019;Chen et al, 2019).…”

Recognition of extracellular DNA by type IV pili promotes biofilm formation by Clostridioides difficile

“…These fibers are established as essential for natural competence (through DNA uptake) in dozens of species of bacteria across a wide variety of bacterial taxa, Gram-positive and Gram-negative ( 35 ). T4F subunits all possess N-terminal TM helices, but their C-terminal headgroups vary considerably, from T4P, which universally have β-sheets packed against the soluble region of the α-helix ( 30 ), to competence pili which have three-helix bundles ( 87 ) to tad/flp pili which appear to have only short loops following the α-helix ( 88 ). Representatives from all three T4F subclasses have been shown to mediate DNA uptake despite the complete lack of identifiable homology between their subunit proteins.…”