Genetic transformation in Streptococcus pneumoniae, Streptococcus mitis and Streptococcus oralis is regulated by secreted peptide pheromones named the competence-stimulating peptide (CSP). Different strains and species of these bacteria produce CSP with different primary sequence. They are termed pheromones CSP-1 (EMRLSKFFRDFILQRKK), CSP-2 (EMRISRIILDFLFLRKK), CSP-153 (DKRLPYFFKHLFSNRTK), CSP-612 (ESRLSRLLRDFIFQIKQ), CSP-676 (ERRIPDVIRSLLFQKRK), and CSP-12261 (EIRQTHNIFFNFFKRR).
Pyroglutamyl (pGlu) peptides may spontaneously form when either Glutamine (Q) or Glutamic acid (E) is located at the sequence N-terminus. The conversion of Q or E to pGlu is a natural occurrence and in general it is believed that the hydrophobic γ-lactam ring of pGlu may play a role in peptide stability against gastrointestinal proteases. Pyroglutamyl peptides are therefore considered a normal subset of such peptides and are included as part of the peptide purity during HPLC analysis.