Crystal structures of a [NiFe] hydrogenase large subunit HyhL in an immature state in complex with a Ni chaperone HypA

Significance The large subunit of [NiFe] hydrogenase undergoes Ni insertion into the active site by the Ni chaperone HypA during its posttranslational process (maturation process). However, the detailed mechanism of the Ni insertion has been elusive. Here, we report the structures of an immature large subunit HyhL in complex with HypA, which enable us to infer a series of conformational changes involved in the Ni delivery. The structures show that the N-terminal tail of HyhL interacts with the Ni-binding domain of HypA. Structural comparison of the immature large subunit HyhL with a mature one reveals that the Ni insertion may induce spatial rearrangement of the N- and C-terminal tails of HyhL.