A Hydrophobic Patch in the Competence-Stimulating Peptide, a Pneumococcal Competence Pheromone, Is Essential for Specificity and Biological Activity

Abstract

Induction of competence for natural genetic transformation in Streptococcus pneumoniae depends on pheromone-mediated cell-cell communication and a signaling pathway consisting of the competence-stimulating peptide (CSP), its membrane-embedded histidine kinase receptor ComD, and the cognate response regulator ComE. Extensive screening of pneumococcal isolates has revealed that two major CSP variants, CSP1 and CSP2, are found in members of this species. Even though the primary structures of CSP1 and CSP2 are about 50% identical, they are highly specific for their respective receptors, ComD1 and ComD2. In the present work, we have investigated the structural basis of this specificity by determining the three-dimensional structure of CSP1 from nuclear magnetic resonance data and comparing the agonist activity of a number of CSP1/CSP2 hybrid peptides toward the ComD1 and ComD2 receptors. Our results show that upon exposure to membranemimicking environments, the 17-amino-acid CSP1 pheromone adopts an amphiphilic ␣-helical configuration stretching from residue 6 to residue 12. Furthermore, the pattern of agonist activity displayed by the various hybrid peptides revealed that hydrophobic amino acids, some of which are situated on the nonpolar side of the ␣-helix, strongly contribute to CSP specificity. Together, these data indicate that the identified ␣-helix is an important structural feature of CSP1 which is essential for effective receptor recognition under natural conditions.

Probing bacterial transmembrane histidine kinase receptor–ligand interactions with natural and synthetic molecules

“…Coevolution of cqsS and cqsA likely maintains ligandreceptor fidelity in each species; at the same time, it allows interspecies signal interference through ligand antagonism mechanisms like those described above. This phenomenon appears to be generally applicable to quorum-sensing systems ranging from the canonical HSL system of cytoplasmic LuxR-type receptors, to the peptide quorum-sensing systems in Gram-positive bacteria (e.g., the Agr system in S. aureus and the Com system in Streptococcus pneumoniae) (47)(48)(49), to the CAI-1-CqsS system studied here.…”

Downsizing human, bacterial, and viral proteins to short water-stable alpha helices that maintain biological potency

“…4A) from Streptococcus pneumoniae (20). This secreted peptide acts on a cell-surface histidine kinase known as ComD, and at low concentrations promotes bacterial growth.…”

“…3-6). Our objective was to compare short peptide sequences corresponding to different protein α-helices (or putative α-helices) in both unconstrained (19,21,23,25) and α-helix-constrained (20,22,24,26) forms. By comparatively assessing the extent of induction of α-helical structure, serum stability, and biological activity, we could determine if this approach had general utility to mimicking protein α-helices in small molecules.…”

“…3B, 4B, 5B, and 6B). Helicity was induced by either two back-to-back cyclic pentapeptides (20,22) or two adjacent cyclic pentapeptides separated by two amino acids (24,26). Helix preorganization resulted in significant enhancements (9-, 10-, 1,000-, and 10,000-fold) in affinity/activity over unconstrained analogues, these functional responses being similar or greater than for the native proteins from which they were derived.…”

“…3B, 4B, 5B, and 6B), but under the same conditions all of the constrained peptides (20,22,24,26) showed α-helicity (45-92%, Figs. 3B, 4B, 5B, and 6B).…”