A third type of hydrogenase catalyzing H₂ activation

Abstract

The activation of molecular hydrogen is of interest both from a chemical and biological viewpoint. The covalent bond of H(2) is strong (436 kJ mol(-1)). Its cleavage is catalyzed by metals or metal complexes in chemical hydrogenation reactions and by metalloenzymes named hydrogenases in microorganisms. Until recently only two types of hydrogenases are known, the [FeFe[-hydrogenases and [NiFe[-hydrogenases. Both types, which are phylogenetically unrelated, harbor in their active site a dinuclear metal center with intrinsic CO and cyanide ligands and contain iron-sulfur clusters for electron transport as revealed by their crystal structures. Fifteen years ago a third type of phylogenetically unrelated hydrogenase was discovered, which has a mononuclear iron active site and is devoid of iron-sulfur clusters. It was initially referred to as "metal free" hydrogenase, but was later renamed iron-sulfur cluster-free hydrogenase or [Fe[-hydrogenase. In this review, we introduce first the [FeFe[-hydrogenases and [NiFe[-hydrogenases, and then focus on the structure and function of the iron-sulfur cluster-free hydrogenase (Hmd) and show that this enzyme contains an iron-containing cofactor. The low-spin iron is complexed by two intrinsic CO-, one sulfur- and one or two N/O ligands and has one open coordination site, which is proposed to be the location of H(2) binding.

Protein-pyridinol thioester precursor for biosynthesis of the organometallic acyl-iron ligand in [Fe]-hydrogenase cofactor

“…The intact cofactor biosynthesized on HcgF could be transferred to the [Fe]-hydrogenase apoenzyme to form its holoenzyme. However, a scaffold function of the other enzymes cannot be excluded 17,29 . Nevertheless, the established thioester activation offers first insights into the chemistry of the subsequent Fe-acyl bond formation and places this reaction in the pathway of Fe centre biosynthesis after iron-carbonyl formation.…”

“…Magnesium chloride, PEG6000, PEG3000 and thiamine were purchased from Merck. 29,30 . GP was generated by irradiation of the extracted FeGP cofactor with room light under N 2 and then purified using HPLC with 6 ml Resource Q column (GE Healthcare) and further purified with Synergi 4 m Polar RP 80 A column (250 Â 4.6 mm, Phenomenex) 30 .…”

Characterization of the Fe Site in Iron−Sulfur Cluster-Free Hydrogenase (Hmd) and of a Model Compound via Nuclear Resonance Vibrational Spectroscopy (NRVS)

“…The iron-sulfur cluster-free hydrogenase (Hmd) is only found in certain methanogenic archaea, and it catalyzes the reversible reduction of methenyltetrahydromethanopterin (methenyl-H 4 MPT + ) with H 2 to methylenetetrahydromethanopterin (methylene-H 4 MPT) and a proton [1][2][3][4][5]. In this reaction, a hydride is transferred from H 2 into the pro-R position of the methylene carbon of methylene-H 4 MPT [3,6] (Chart 1).…”

Spin distribution of the H-cluster in the Hox–CO state of the [FeFe] hydrogenase from Desulfovibrio desulfuricans: HYSCORE and ENDOR study of 14N and 13C nuclear interactions

“…The third class of hydrogenases, the [Fe] hydrogenases, contain a single iron atom in their cofactors [12][13][14]. This type of enzyme is also called the iron-sulfur-cluster-free hydrogenase [15], or ''Hmd'' (H 2 -forming N 5 ,N 10 -methylenetetrahydromethanopterin dehydrogenase).…”