Structural Analysis of the Peptide Pheromone Receptor PlnB, a Histidine Protein Kinase fromLactobacillus plantarum

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Abstract
Intercellular communication plays a key role in the regulation of several physiological processes in gram-positive bacteria. Cell-cell communication is often mediated by secreted inducer peptide pheromones (IPs), which upon reaching a threshold concentration in the environment specifically activate a cognate membrane-localized histidine protein kinase (HPK). Interestingly, the majority of IP-activated HPKs fall into one distinct subfamily (HPK10). As part of an effort to study the mechanism underlying pheromone-mediated activation of the HPK10 subfamily, the present work investigated the membrane topology of PlnB from Lactobacillus plantarum. Gene fusion experiments with Escherichia coli and Lactobacillus sakei, using alkaline phosphatase, β-lactamase, and β-galactosidase reporter fusions, suggested that PlnB is anchored to the cytoplasmic membrane via seven transmembrane segments. By domain switching between HPK10 members, it was demonstrated that the determinants for pheromone binding and specificity are contained within the transmembrane domain. The results also indicate that the mechanism of signal transduction, in which the final transmembrane segment apparently plays a key role, is conserved between members of the HPK10 subfamily.