Gram-negative bacteria secrete many proteins, including hemophores, via the type 1 secretion system (T1SS). The latter consists of three proteins powered by the inner membrane ABC protein. Proteins secreted by T1SS have a C-terminal signal, essential for secretion that interacts with the ABC protein. Muriel Masi and Cecile Wandersman of the Pasteur Institute, Paris, show that the Serratia marcescens hemophore has regions located outside of the C-terminal signal sequence which they call anchoring sites, that bind to the ABC protein, and that these regions are numerous, distributed throughout the protein, and most likely linear. The T1SS is a transient construct, and these anchoring sites drive its assembly, maintain its integrity, and maximize hemophore secretion. The C-terminal signal triggers ATP hydrolysis and disassembly of the T1SS proteins. This team plans to test whether anchoring sites are present on other T1SS substrates. The research could have positive implication for production of recombinant proteins. "Many recombinant proteins with potential therapeutic properties are difficult to produce and purify in an active form," says Wandersman. "We will test whether the insertion of the recombinant proteins between the anchoring sites and the C-terminal secretion signal sequence improves their secretion of recombinant proteins by T1SS, which would simplify their purification of such proteins."

(M. Masi and C. Wandersman. 2010. Multiple signals direct the assembly and function of a type 1 secretion system. J. Bacteriol. 192:3861-3869.)