Atomic structures and reaction mechanisms of proteins involved in transfer and insertion of molybdenum cofactor and heme

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This project is a collaborative project interacting with four other projects within the Forschergruppe. The aim is to crystallize the following proteins and solve their atomic structures in order to decipher their hitherto unknown reaction mechanisms: (1) The molybdenum cofactor (Moco)-carrying ABA3 sulfurase of Arabidopsis alone and in complex with its target enzyme xanthine dehdrogenase and/or aldehyde oxidase. Here we want to unravel the mechanism by which ABA3 achieves the insertion of Moco and the sulfuration of the Mo-center as required by xanthine dehydrogenase and aldehyde oxidase. (2) The Arabidopsis thaliana Moco-donor protein Cnx1 in complex with its substrate MPT-AMP. Structure-guided mutagenesis will provide insight into MPT-AMP hydrolysis and will shed light onto the mechanism how Moco is presented by the Cnx1 Moco-donor platform. (3) The heme-binding protein HemW from Escherichia coli with and without bound heme. Since the [4Fe-4S] cluster and S-adenoslymethionine containing protein is dimerizing upon heme binding and subsequently transferring electrons, involved structural changes and possible catalytic principle are of interest. (4) The heme d1 insertion protein NirN in complex with heme d1 and in complex with its target protein NirS. Here we want to analyze how heme d1 binding in NirN differs from that in NirS and how the two proteins interact with each other for heme d1 transfer from NirN to NirS.