Assembly of Tat-dependent [NiFe] hydrogenases: identification of precursor-binding accessory proteins.

The Escherichia coli twin-arginine translocation (Tat) system serves to export fully folded protein substrates across the bacterial cytoplasmic membrane. Respiratory [NiFe] hydrogenases are synthesised as precursors with twin-arginine signal peptides and transported as large, cofactor-containing, multi-subunit complexes by the Tat system. Cofactor insertion and assembly of [NiFe] hydrogenases requires coordination of networks of accessory proteins. In this work we utilise a bacterial two-hybrid assay to demonstrate protein-protein interactions between the uncharacterised chaperones HyaE and HybE with Tat signal peptide-bearing hydrogenase precursors. It is proposed that the chaperones act at a 'proofreading' stage in hydrogenase assembly and police the protein transport pathway preventing premature targeting of Tat-dependent hydrogenases.