Site-directed mutagenesis of the hydrogenase signal peptide consensus box prevents export of a beta-lactamase fusion protein.

A secretion vector, pVN1, expressing the [NiFe] hydrogenase signal peptide of Desulfovibrio vulgaris Hildenborough fused to beta-lactamase from Escherichia coli was constructed in order to study the unusual characteristics of hydrogenase signal peptides, which share a strictly conserved sequence, the consensus box: R-R-X-F-X-K. Although the hydrogenase signal peptide-beta-lactamase fusion protein was processed much more slowly than the fusion of beta-lactamase with its own signal peptide, the system mimicked several features expected for hydrogenase biosynthesis in E. coli, including increased export under anaerobic conditions. Site-directed mutagenesis of R(-28), the first arginine residue of the consensus box, to a glutamate completely inhibited export and processing of the fusion protein. The same mutation of R(-33), located outside the consensus box, had almost no effect. The data indicate a specific role for the consensus box sequence in the export mechanism for hydrogenase.