The multi-step biosynthesis of the [NiFe]-hydrogenase enzyme involves a variety of accessory proteins. To further understand this process, a Strep-tag II variant of the large subunit of Escherichia coli hydrogenase 3, HycE, was constructed to enable isolation of protein complexes. A complex with SlyD, a chaperone protein implicated in hydrogenase production through association with the nickel-binding accessory protein HypB, was observed. A SlyD-HycE interaction preceding both iron and nickel insertion to the enzyme was detected, mediated by the chaperone domain of SlyD, and independent of HypB. These results support a model of several roles for SlyD during hydrogenase maturation. Structured summary: HycE physically interacts with HypA, HypB and SlyD by cross linking study (view interaction) HycE physically interacts with DnaK and GroEL by cross linking study (view interaction) HypB physically interacts with SlyD by cross linking study (view interaction) HycE physically interacts with SlyD by cross linking study (view interaction 1, 2) (C) 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.