Crystallographic analysis of Escherichia coli type I signal peptidase in complex with peptide-based inhibitors

Escherichia coli type I signal peptidase (SPase I) is a membrane-bound endopeptidase that cleaves amino-terminal signal peptides from secreted proteins and some membrane proteins. To contribute to the structure-based design effort for developing a novel class of antibiotics, the X-ray crystal structures of peptide-based inhibitors with SPase I have been solved. Nine complexes of SPase I with inhibitor were co-crystallized, five of which diffracted to 2.6 Å or better. Two crystal structures were solved using molecular replacement and refined. Crystallographic analysis of these two SPase I-inhibitor complexes will be useful for evaluating and optimizing these novel antibiotic drug candidates. The crystal contacts and structural variations of the SPase I molecules from each SPase I crystal structure solved to date were analyzed and compared in a first step towards the design of new constructs of SPase I that may crystallize more readily and in a more ordered fashion.