Investigating the Effects of N-Methyl Modifications on Activity of a Truncated Group I Competence Stimulating Peptide (CSP1) on Quorum Sensing in Streptococcus pneumoniae
Bacterial infections are becoming increasingly difficult to treat as more bacteria develop antibiotic resistance. Our research aims to produce a therapeutic to block bacterial communication, rendering bacteria non-pathogenic without killing them, thus avoiding driving the evolution of resistant strains. Bacteria communicate through a phenomenon called quorum sensing, in which bacteria release signal molecules to indicate their population size and density. Once a population is large enough, it engages in behaviors that are effective only when the whole group, rather than individual bacterium, exhibit them. This phenomenon can induce previously non-pathogenic bacteria populations to attack their hosts. S. pneumoniae uses a 17-amino acid long peptide called competence stimulating peptide (CSP) to communicate. At a threshold concentration, CSP binds and activates a receptor called comD, starting a signaling cascade ending with bacteria exhibiting group behaviors such as virulence. CSP analogs that outcompete the native peptide for binding to comD could impede bacterial communication, and therefore, pathogenicity. However, finding an effective therapeutic is complicated by the fact that different strains of S. pneumoniae have different signaling molecules called CSP-1 and CSP-2 that will only bind respectively to comD-1 and comD-2, respectively. Our previous research has shown CSP-1 interacts slightly more effectively with comD-2 than CSP-2 will with comD-1, and that the final two residues on both peptides are unnecessary for binding. Therefore, the purpose of this project was to complete an N-methyl scan of a 15-amino acid long CSP-1 analog to determine the importance of different backbone hydrogen bonds on the activity of the peptide. Solid-phase peptide synthesis was utilized to construct a library of 15 N-methyl analogs, and cell-based reporter assays were conducted to evaluate the ability of the different analogs to modulate quorum sensing in both S. pneumoniae specificity groups
