Structural studies of the transpeptidase domain of PBP1a fromStreptococcus pneumoniae

The synthesis of the bacterial cell wall requires enzymes which are localized both in the cytoplasm and in the periplasm. Penicillin-binding proteins (PBPs) catalyze the last, crucial steps in peptidoglycan biosynthesis and several of them are essential for bacterial survival. High-molecular-mass PBPs can be bifunctional (class A) or monofunctional (class B) and to date no structural information on any class A PBP is available. To initiate the determination of the three-dimensional structure of a class A PBP, crystals of the transpeptidase domain of PBP1a from Streptococcus pneumoniae were prepared by limited proteolysis of the full-length molecule and purification by anion-exchange chromatography and gel filtration. The samples crystallize in space group C222(1), contain one molecule per asymmetric unit and diffract X-rays to 2.7 A. Selenomethionine-labelled crystals have been prepared and structure solution is under way.