Crystal Structure of HydG from Carboxydothermus hydrogenoformans: A Trifunctional [FeFe]-Hydrogenase Maturase

• Published in: Chembiochem : a European journal of chemical biology 2015-02, Vol.16 (3), p.397-402
• Main Authors: Nicolet, Yvain, Pagnier, Adrien, Zeppieri, Laura, Martin, Lydie, Amara, Patricia, Fontecilla-Camps, Juan C.
• Format: Article
• Language: English
• Subjects: [FeFe]-hydrogenase maturasetyrosine lyase; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacteriology; Binding Sites; Crystal structure; Crystallography, X-Ray; CC bond cleavage; Hydrogenase - chemistry; Hydrogenase - metabolism; Iron-Sulfur Proteins - chemistry; Iron-Sulfur Proteins - metabolism; Life Sciences; Models, Molecular; Protein Conformation; radical SAM enzyme; radicals; reduction; S-Adenosylmethionine - chemistry; Thermoanaerobacterium - enzymology; Tyrosine - chemistry
• ISSN: 1439-4227; 1439-7633
• DOI: 10.1002/cbic.201402661

The structure of the radical S‐adenosyl‐L‐methionine (SAM) [FeFe]‐hydrogenase maturase HydG involved in CN−/CO synthesis is characterized by two internal tunnels connecting its tyrosine‐binding pocket with the external medium and the C‐terminal Fe4S4 cluster‐containing region. A comparison with a tryptophan‐bound NosL structure suggests that substrate binding causes the closing of the first tunnel and, along with mutagenesis studies, that tyrosine binds to HydG with its amino group well positioned for H‐ion by SAM. In this orientation the dehydroglycine (DHG) fragment caused by tyrosine CαCβ bond scission can readily migrate through the second tunnel towards the C‐terminal domain where both CN− and CO are synthesized. Our HydG structure appears to be in a relaxed state with its C‐terminal cluster CysX2CysX22Cys motif exposed to solvent. A rotation of this domain coupled to Fe4S4 cluster assembly would bury its putatively reactive unique Fe ion thereby allowing it to interact with DHG. HydG catalyzes the synthesis of the [FeFe] hydrogenase active‐site CN− and CO ligands from tyrosine. Its structure shows that the three catalytic activities are compartmentalized, with their sites being connected by internal tunnels. The C‐terminal Fe4S4 cluster might oscillate between a buried conformation required for Fe(CO)x(CN) synthesis and an exposed one for its delivery to the scaffold HydF.