title: Conformation of NADP+ bound to a type II dihydrofolate reductase.
abstract: Type II dihydrofolate reductases (DHFRs) encoded by the R67 and R388 plasmids are sequence and structurally different from known chromosomal DHFRs. These plasmid-derived DHFRs are responsible for confering trimethoprim resistance to the host strain. A derivative of R388 DHFR, RBG200, has been cloned and its physical properties have been characterized. This enzyme has been shown to transfer the pro-R hydrogen of NADPH to its substrate, dihydrofolate, making it a member of the A-stereospecific class of dehydrogenases [Brito, R. M. M., Reddick, R., Bennett, G. N., Rudolph, F. B., & Rosevear, P. R. (1990) Biochemistry 29,9825]. Two distinct binary RBG200.NADP+ complexes were detected. Addition of NADP+ to RBG200 DHFR results in formation of an initial binary complex, conformation I, which slowly interconverts to a second more stable binary complex, conformation II. The binding of NADP+ to RBG200 DHFR in the second binary complex was found to be weak, KD = 1.9 +/- 0.4 mM. Transferred NOEs were used to determine the conformation of NADP+ bound to RBG200 DHFR. The initial slope of the NOE buildup curves, measured from the intensity of the cross-peaks as a function of the mixing time in NOESY spectra, allowed interproton distances on enzyme-bound NADP+ to be estimated. The experimentally measured distances were used to define upper and lower bound distance constraints between proton pairs in distance geometry calculations. All NADP+ structures consistent with the experimental distance bounds were found to have a syn conformation about the nicotinamide-ribose (X = 94 +/- 26 degrees) and an anti conformation about the adenine-ribose (X = -92 +/- 32 degrees) glycosidic bonds.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, Rice University, Houston, Texas 77005.
authors.forename: R M
authors.initials: RM
authors.lastname: Brito
authors.forename: F B
authors.initials: FB
authors.lastname: Rudolph
authors.forename: P R
authors.initials: PR
authors.lastname: Rosevear
mesh_terms: D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008958:Models, Molecular; D008968:Molecular Conformation; D009249:NADP / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010957:Plasmids; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D009249:NADP; D013762:Tetrahydrofolate Dehydrogenase