Redox tuning of the H-cluster by second coordination sphere amino acids in the sensory [FeFe] hydrogenase from <i>Thermotoga maritima</i>
Nipa Chongdar, Patricia Rodríguez‐Maciá, Edward J. Reijerse, Wolfgang Lubitz, Hideaki Ogata, James A. Birrell
Abstract
has low activity and displays a very positive redox potential for the [2Fe] subcluster compared to that of the highly active prototypical enzymes. Using site directed mutagenesis, we investigate how second coordination sphere interactions of the protein environment with the H-cluster in HydS influence the catalytic, spectroscopic and redox properties of the H-cluster. In particular, mutation of the non-conserved serine 267, situated between the [4Fe-4S] and [2Fe] subclusters, to methionine (conserved in prototypical catalytic enzymes) gave a dramatic decrease in activity. Infra-red (IR) spectroelectrochemistry revealed a 50 mV lower redox potential for the [4Fe-4S] subcluster in the S267M variant. We speculate that this serine forms a hydrogen bond to the [4Fe-4S] subcluster, increasing its redox potential. These results demonstrate the importance of the secondary coordination sphere in tuning the catalytic properties of the H-cluster in [FeFe] hydrogenases and reveal a particularly important role for amino acids interacting with the [4Fe-4S] subcluster.