The Penicillin-Binding Proteins (PBPs) are transpeptidases that catalyze crosslinking in the bacterial cell wall and the molecular targets of the ß-lactam antibiotics
The Penicillin-Binding Proteins (PBPs) are transpeptidases that catalyze crosslinking in the bacterial cell wall and the molecular targets of the penicillin antibiotics. Here, we report an integrative structural biology study of PBP1 from Staphylococcus aureus (saPBP1), providing mechanistic clues about its function and regulation during cell division. A significant result provided in this work is the unexpected arrangement of the PASTA domains respect to the rest PBP1 domains, pointing to profound functional implications. Thus, although PBP1-PASTA domains preserve their compact fold, SAXS and molecular-dynamics simulations revealed that they are conformationally mobile and separated of transpeptidase domain in contrast with their homologues in PBP2x from Streptococcus pneumoniae and Streptococcus thermophilus. A series of crystallographic complexes with β-lactam antibiotics (as inhibitors) and penta-Glycine (as a substrate mimetic) allowed the molecular characterization of both inhibition by antibiotics and binding for the donor and acceptor peptidoglycan strands. Mass-spectrometry experiments with synthetic peptidoglycan fragments revealed binding by PASTA domains in coordination with the remaining domains. Collectively, our structural and modelling studies allowed us, for the first time, to decipher key structural features and differences between saPBP1 and other PBPs. The observed mobility of the PASTA domains in saPBP1 could play a crucial role for in vivo interaction with its glycosyltransferase partner in the membrane or with other components of the divisome machinery, as well as for coordination of transpeptidation and polymerization processes in the bacterial divisome.
