GramPos_pilinBB is one of the major backbone units of Gram-positive pili, such as those from S.pneumoniae. There are three major pilin subunits that form the polymeric backbone of the pilin from S. pneumoniae, constructed of three transthyretin-like, CnaB, domains along with a crucial N-terminal domain, D1. The three Cna-B like domains are stabilised by internal Lys-Asn isopeptdie bonds, Gram-positive pili are formed from a single chain of covalently linked subunit proteins (pilins), usually comprising an adhesin at the distal tip, a major pilin that forms the polymer shaft and a minor pilin that mediates cell wall anchoring at the base.
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