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Megta, Abhin Kumar and Pratap, Shivendra and Kant, Abhiruchi and Palva, Airi and von Ossowski, Ingemar and Krishnan, Vengadesan (2020) Crystal structure of the atypically adhesive SpaB basal pilus subunit: Mechanistic insights about its incorporation in lactobacillar SpaCBA pili. Current Research in Structural Biology, 2. pp. 229-238. ISSN 2665928X

Crystal structure of the atypically adhesive SpaB basal pilus subunit Mechanistic insights about its incorporation in lactobacillar SpaCBA pili.pdf

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To successfully colonize a host or environment, certain genera and species of Gram-positive bacteria have evolvedto utilize the so-called sortase-dependent pilus, a long multi-subunit and non-flagellar surface adhesin. Oneexample of this isLactobacillus rhamnosusGG, a gut-adapted probiotic strain that produces SpaCBA pili. Thesestructures are covalent hetero-oligomers built from three types of pilin subunit, each with a specific location andfunction (i.e., backbone SpaA for length, tip SpaC for adhesion, and basal SpaB for anchoring). Functionally, theSpaCBA pilus exhibits a promiscuous affinity for components on intestinal surfaces (e.g., mucus, collagen, andepithelial cells), which is largely attributed to the SpaC subunit. Then again, the basal SpaB pilin, in addition toacting as the terminal subunit during pilus assembly, displays an out of character mucoadhesive function. Toaddress the structural basis of this unusual dual functionality, we reveal the 2.39 Å resolution crystal structure ofSpaB. SpaB consists of one immunoglobulin-like CnaB domain and contains a putative intermolecular isopeptidebond-linking lysine and internal isopeptide bond-asparagine in an FPKNpilin motif within the C-terminal end.Remarkably, we found that a C-terminal stretch of positively charged lysine and arginine residues likely accountsfor the atypical mucoadhesiveness of SpaB. Although harboring an autocatalytic triad of residues for a potentialinternal isopeptide interaction, the SpaB crystal structure lacked the visible electron density for intact bondformation, yet its presence was subsequently confirmed by mass spectral analysis. Finally, we propose a structuralmodel that captures the exclusive basal positioning of SpaB in the SpaCBA pilus.

Item Type: Article
Subjects: Biomedical Science
Biochemical and Biophysical Sciences
Depositing User: RCB Library
Date Deposited: 01 Jan 2021 12:51
Last Modified: 02 Aug 2021 07:53
URI: http://rcb.sciencecentral.in/id/eprint/557

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