An electrostatic interaction between BlpC and BlpH influences pheromone specificity in the control of bacteriocin production and immunity in Streptococcus pneumoniae.

J Bacteriol. 2015 Jan 26. pii: JB.02432-14. [Epub ahead of print]

An electrostatic interaction between BlpC and BlpH influences pheromone specificity in the control of bacteriocin production and immunity in Streptococcus pneumoniae.

Pinchas MD1, LaCross NC2, Dawid S3.

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Abstract

The blp locus of Streptococcus pneumoniae secretes and regulates bacteriocins, which mediate both intra- and interspecific competition in the human nasopharynx. There are four major alleles of the gene blpH, which encodes the receptor responsible for activating the blp locus when bound to one of four distinct peptide pheromones (BlpC). The allelic variation of blpH is presumably explained by a need to restrict cross talk between competing strains. The BlpH protein sequences have polymorphisms distributed throughout the entire sequence, making identification of the peptide binding site difficult to predict. To identify the pheromone binding sites that dictate pheromone specificity, we have characterized the four major variants and two naturally occurring chimeric versions of blpH in which recombination events appear to have joined two distinct blpH alleles together. Using these allelic variants, a series of lab generated chimeric blpH alleles, and site-directed mutants of both the receptor and peptide, we have demonstrated that BlpC binding to some BlpH types involves an electrostatic interaction between the oppositely charged residues of BlpC and the first transmembrane domain of BlpH. An additional recognition site was identified in the second extracellular loop. We identified naturally occurring BlpH types that have the capacity to respond to more than one BlpC type; however, this change in specificity results in a commensurate drop in overall sensitivity. These natural recombination events were presumably selected for to balance the need to sense bacteriocin secreting neighbors with the need to turn on bacteriocin production at a low density.

IMPORTANCE:

Bacteria use quorum sensing to optimize gene expression to accommodate for local bacterial density and diffusion rates. To prevent interception of quorum signals by neighboring strains, single species often encode strain-specific signal/receptor pairs. The blp locus in Streptococcus pneumoniae that drives bacteriocin secretion is controlled by quorum sensing that involves the interaction of the signal/receptor pair, BlpC/BlpH. We show that the pneumococcal population can be divided into several distinct BlpC/H pairs, however, there are examples of naturally occurring chimeric receptors that can bind to more than one BlpC type. The tradeoff for this broadened specificity is a loss of overall receptor sensitivity. This suggests that under certain conditions, the advantage of signal interception can trump the requirements for self-induction.

Copyright © 2015, American Society for Microbiology. All Rights Reserved.

PMID: 25622617 [PubMed - as supplied by publisher]