Document Detail

The 3-D structure of a folate-dependent dehydrogenase/cyclohydrolase bifunctional enzyme at 1.5 A resolution.
MedLine Citation:
PMID:  9519408     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: The interconversion of two major folate one-carbon donors occurs through the sequential activities of NAD(P)-dependent methylene[H4]folate dehydrogenase (D) and methenyl[H4]folate cyclohydrolase (C). These activities often coexist as part of a multifunctional enzyme and there are several lines of evidence suggesting that their substrates bind at overlapping sites. Little is known, however, about the nature of this site or the identity of the active-site residues for this enzyme family. RESULTS: We have determined, to 1.5 A resolution, the structure of a dimer of the D/C domain of the human trifunctional cytosolic enzyme with bound NADP cofactor, using the MAD technique. The D/C subunit is composed of two alpha/beta domains that assemble to form a wide cleft. The cleft walls are lined with highly conserved residues and NADP is bound along one wall. The NADP-binding domain has a Rossmann fold, characterized by a modified diphosphate-binding loop fingerprint-GXSXXXG. Dimerization occurs by antiparallel interaction of two NADP-binding domains. Superposition of the two subunits indicates domain motion occurs about a well-defined hinge region. CONCLUSIONS: Analysis of the structure suggests strongly that folate-binding sites for both activities are within the cleft, providing direct support for the proposed overlapping site model. The orientation of the nicotinamide ring suggests that in the dehydrogenase-catalyzed reaction hydride transfer occurs to the pro-R side of the ring. The identity of the cyclohydrolase active site is not obvious. We propose that a conserved motif-Tyr52-X-X-X-Lys56- and/or a Ser49-Gln100-Pro102 triplet have a role in this activity.
M Allaire; Y Li; R E MacKenzie; M Cygler
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Structure (London, England : 1993)     Volume:  6     ISSN:  0969-2126     ISO Abbreviation:  Structure     Publication Date:  1998 Feb 
Date Detail:
Created Date:  1998-05-07     Completed Date:  1998-05-07     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  101087697     Medline TA:  Structure     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  173-82     Citation Subset:  IM    
Biotechnology Research Institute, Montréal, Québec, Canada.
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MeSH Terms
Aminohydrolases / chemistry*
Crystallography, X-Ray
Methylenetetrahydrofolate Dehydrogenase (NADP) / chemistry*
Models, Molecular
Multienzyme Complexes / chemistry*
NADP / chemistry
Protein Conformation
Protein Structure, Secondary
Protein Structure, Tertiary*
Reg. No./Substance:
0/Multienzyme Complexes; 0/methylene tetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase; 53-59-8/NADP; EC Dehydrogenase (NADP); EC 3.5.4.-/Aminohydrolases

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