32] Engineering for protein secretion in gram-positive bacteria

Abstract

The chapter presents a discussion on engineering for protein secretion in gram-positive bacteria. The ability of gram-positive bacteria to excrete proteins into the medium makes them the more favorable candidates as the host organisms for the production of secreted proteins. Some members of this group of bacteria produce a number of economically important exoenzymes, such as cellulases, α-amylase, and proteases, in large quantity. The chapter discusses a number of examples of expression and directed secretion of heterologous proteins in gram-positive bacteria. Generally, the precursors to all secreted proteins contain an amino terminal extension of about 20 to 35 residues in length known as the “signal peptide.” This fragment, although relatively short in length, plays a central role in protein translocation across membranes. Mostly, this signal peptide is removed from the precursor by signal peptidases either co- or post-translationally, resulting in the formation of the mature protein in the designated extracytoplasmic locations. Signal peptide can be divided into three distinct regions based on their common structural features, which are as follows: (1) the amino terminal region, which contains one or more positively charged residues, (2) a stretch of 10–20 hydrophobic or neutral residues, and (3) the carboxy end four to seven residues, including the signal peptidase cleavage site sequence. The majority of the secretion studies in gram-positive bacteria have been conducted using B. subtilis.