21] Bacterial leader peptidase 1

Abstract

Publisher Summary This chapter highlights bacterial leader peptidase 1. It describes the purification of leader peptidase, its substrate specificity, sequence homology of the leader peptidase 1 genes, and techniques to probe the structure and function of this protein. Proteins that are secreted out of the cell or translocated across lipid bilayers are usually made with N-terminal extension peptides, termed “leader sequences.” In bacteria, two separate leader peptidases process proteins. Leader peptidase 1 cleaves the majority of the preproteins destined to the cell surface, whereas leader peptidase 2 only processes preproteins that have been first modified with a lipid molecule at the +1 position. The Escherichia coli leader peptidase 1 is an integral membrane protein of 323 amino acid residues. Its physiological role is to release exported proteins from the membrane by removing the leader sequence. Leader peptidase can be assayed using a radiolabeled preprotein substrate or a peptide substrate. It is purified by membrane isolation, Triton X-100 extraction, diethylaminoethyl (DEAE) chromatography, and chromatofocusing.