PASTA domain of PBP2x-like proteins, first repeat. Penicillin-binding proteins (PBPs) are the major targets for beta-lactam antibiotics, like penicillins and cephalosporins. Beta-lactam antibiotics specifically inhibit transpeptidase activity by acylating the active site serine. PBPs catalyze key steps in the synthesis of the peptidoglycan, such as the interconnecting of glycan chains (polymers of N-glucosamine and N-acetylmuramic acid residues) and the cross-linking (transpeptidation) of short stem peptides, which are connected to glycan chains. Peptidoglycan is essential in cell division and protects bacteria from osmotic shock and lysis. PBP2x is one of the two monofunctional high molecular mass PBPs in Streptococcus pneumoniae and has been seen as the primary PBP target in beta-lactam-resistant strains. The PASTA domain is found at the C-termini of several PBPs and bacterial serine/threonine kinases. The name PASTA is derived from PBP and Serine/Threonine kinase Associated domain.