1xwf
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(New page: 200px<br /><applet load="1xwf" size="450" color="white" frame="true" align="right" spinBox="true" caption="1xwf, resolution 2.8Å" /> '''K185N mutated S-adeno...)
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Revision as of 04:16, 21 November 2007
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K185N mutated S-adenosylhomocysteine hydrolase
Overview
S-adenosylhomocysteine hydrolase (AdoHcyase) catalyzes the hydrolysis of, S-adenosylhomocysteine (AdoHcy) to form adenosine and homocysteine. The, crystal structure of the K185N mutated enzyme, which has weak catalytic, activity (0.1%), has been determined at 2.8 A resolution and supports the, previously predicted mechanism [Takata, Y., Yamada, T., Huang, Y., Komoto, J., Gomi, T., Ogawa, H., Fujioka, M., & Takusagawa, F. (2002). Catalytic, mechanism of S-adenosylhomocysteine hydrolase. Site-directed mutagenesis, of Asp-130, Lys-185, Asp-189, and Asn-190. J. Biol. Chem. 277, 22670-22676]. The mutated enzyme has an intermediate structure between the, open and closed conformation, observed in the substrate-free enzyme and in, the inhibitor complexes, respectively. H54, H300, and H352 were mutated to, asparagine, respectively, to identify the roles of the histidine residues, in catalysis. The kinetic data of H54N, H300N, and H354N mutated enzymes, suggest that H54 is the amino acid residue that acts as a general, acid/base to cleave the C5'-S(D) bond of AdoHcy. The E155Q mutated enzyme, retained a large portion of the catalytic activity (31%), while the E155D, mutated enzyme lost most of it (0.3%). The NADH accumulation measurements, of the mutated enzymes indicated that the C3'-oxidation and the C4'-proton, abstraction are a concerted event and the C5'-S(D) bond cleavage is an, independent event. The C4'-proton exchange measurements indicate that the, enzyme has an open conformation when AdoHcy is converted to 3'-keto-4', 5'-dehydro-Ado in the active site. With the results of this study and, those of the previous studies, a detailed catalytic mechanism of AdoHcyase, is described. K185 facilitates the C3'-oxidation, D130 abstracts the, C4'-proton, D189, and E155 act as a communicator between the concerted, C3'-oxidation and C4'-proton abstraction, and H54 plays as a general acid, to cleave the C5'-S(D) bond of AdoHcy.
About this Structure
1XWF is a Single protein structure of sequence from Rattus norvegicus with NAD and ADN as ligands. Active as Adenosylhomocysteinase, with EC number 3.3.1.1 Full crystallographic information is available from OCA.
Reference
Catalytic mechanism of S-adenosylhomocysteine hydrolase: roles of His 54, Asp130, Glu155, Lys185, and Aspl89., Yamada T, Takata Y, Komoto J, Gomi T, Ogawa H, Fujioka M, Takusagawa F, Int J Biochem Cell Biol. 2005 Nov;37(11):2417-35. PMID:16061414
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