Identification of the Amino Acid Sequence of the Mature PhrA Signaling Peptide of Streptococcus pneumoniae
Authors:Sharon Hoover, Amilcar Perez
Mentor:Beth Lazazzera, Professor of Microbiology, Immunology, and Molecular Genetics Department, University of California Los Angeles
Quorum-sensing (QS) is the ability of bacterial cells to monitor population density and in return affect gene expression. The phrA/tprA cassette of Streptococcus pneumoniae (SP), a common human pathogen, resembles QS systems found in other Gram-positive bacteria. Consistent with this, TprA was previously found to be a negative regulator of phrA expression, and PhrA induced its own expression, presumably by antagonizing the activity of TprA. The PhrA protein is predicted to be secreted and cleaved to release a mature peptide from its C-terminal domain, which is then predicted to be imported into the cytoplasm to bind to TprA. Here we sought out to remove the C-terminal residues of phrA in order to confirm the identity of mature peptide. To determine this sequence, we create phrA alleles that express C-terminally truncated PhrA proteins. The truncation alleles of phrA were transformed into a SP strain that lacks the wild-type copy of phrA and contains a phrA-lacZ reporter. Expression levels of lacZ in cells containing either full-length or a truncated phrA allele were measured to determine the residues vital for the auto-inducing function of PhrA. Transformants containing any of the deletion constructs resulted in loss of phrA-lacZ expression, revealing that the C-terminal of PhrA possesses residues vital for mature-PhrA function. This study will aid in understanding the mechanism of gene expression controlled by PhrA and TprA and the role of these proteins in mediating a QS signal.