Crystal Structure Analysis of [NiFe] Hydrogenase Maturation Proteins

Introduction [NiFe]-hydrogenases harbor a complex metal cofactor, NiFe(CN)2CO, in their active sites. Its biosynthesis requires specific maturation machinery, in which six Hyp proteins (HypABCDEF) play key roles. Four Hyp proteins (HypCDEF) are involved in the biosynthesis and incorporation of the Fe(CN)2CO group. After Fe insertion, HypA and HypB insert the Ni ion into the hydrogenase large subunit. Finally, proteases such as HybD and HycI are involved in the cleavage of the C-terminal residues of the large subunits. We determined crystal structures of all Hyp proteins and obtained various knowledge of the maturation system. However, the transient Hyp protein complex formed in this process is not fully understood. In this study, we have determined crystal structures of the HypA / ATPase-type HypB (HypBAT) complex from Thermococcus kodakarensis, providing the structural basis of concerted actions of these proteins for Ni insertion [1]. In addition, we have also determined crystal structure of the maturation protease HybD to reveal its substrate recognition mechanism [2].