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Evaluation by mutagenesis of the roles of His309, His315, and His319 in the coenzyme site of pig heart NADP-dependent isocitrate dehydrogenase.
Biochemistry. 2002 Apr 30; 41(17):5637-43.B

Abstract

Sequence alignment predicts that His(309) of pig heart NADP-dependent isocitrate dehydrogenase is equivalent to His(339) of the Escherichia coli enzyme, which interacts with the coenzyme in the crystal structure [Hurley et al. (1991) Biochemistry 30, 8671-8688], and porcine His(315) and His(319) are close to that site. The mutant porcine enzymes H309Q, H309F, H315Q, and H319Q were prepared by site-directed mutagenesis, expressed in E. coli, and purified. The H319Q mutant has K(m) values for NADP, isocitrate, and Mn(2+) similar to those of wild-type enzyme, and V(max) = 20.1, as compared to 37.8 micromol of NADPH min(-1) (mg of protein)(-1) for wild type. Thus, His(319) is not involved in coenzyme binding and has a minimal effect on catalysis. In contrast, H315Q exhibits a K(m) for NADP 40 times that of wild type and V(max) = 16.2 units/mg of protein, with K(m) values for isocitrate and Mn(2+) similar to those of wild type. These results implicate His(315) in the region of the NADP site. Replacement of His(309) by Q or F yields enzyme with no detectable activity. The His(309) mutants bind NADPH poorly, under conditions in which wild type and H319Q bind 1.0 mol of NADPH/mol of subunit, indicating that His(309) is important for the binding of coenzyme. The His(309) mutants bind isocitrate stoichiometrically, as do wild-type and the other mutant enzymes. However, as distinguished from the wild-type enzyme, the His(309) mutants are not oxidatively cleaved by metal isocitrate, implying that the metal ion is not bound normally. Since circular dichroism spectra are similar for wild type, H315Q, and H319Q, these amino acid substitutions do not cause major conformational changes. In contrast, replacement of His(309) results in detectable change in the enzyme's CD spectrum and therefore in its secondary structure. We propose that His(309) plays a significant role in the binding of coenzyme, contributes to the proper coordination of divalent metal ion in the presence of isocitrate, and maintains the normal conformation of the enzyme.

Authors+Show Affiliations

Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.No affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

11969425

Citation

Huang, Yu Chu, and Roberta F. Colman. "Evaluation By Mutagenesis of the Roles of His309, His315, and His319 in the Coenzyme Site of Pig Heart NADP-dependent Isocitrate Dehydrogenase." Biochemistry, vol. 41, no. 17, 2002, pp. 5637-43.
Huang YC, Colman RF. Evaluation by mutagenesis of the roles of His309, His315, and His319 in the coenzyme site of pig heart NADP-dependent isocitrate dehydrogenase. Biochemistry. 2002;41(17):5637-43.
Huang, Y. C., & Colman, R. F. (2002). Evaluation by mutagenesis of the roles of His309, His315, and His319 in the coenzyme site of pig heart NADP-dependent isocitrate dehydrogenase. Biochemistry, 41(17), 5637-43.
Huang YC, Colman RF. Evaluation By Mutagenesis of the Roles of His309, His315, and His319 in the Coenzyme Site of Pig Heart NADP-dependent Isocitrate Dehydrogenase. Biochemistry. 2002 Apr 30;41(17):5637-43. PubMed PMID: 11969425.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Evaluation by mutagenesis of the roles of His309, His315, and His319 in the coenzyme site of pig heart NADP-dependent isocitrate dehydrogenase. AU - Huang,Yu Chu, AU - Colman,Roberta F, PY - 2002/4/24/pubmed PY - 2002/5/30/medline PY - 2002/4/24/entrez SP - 5637 EP - 43 JF - Biochemistry JO - Biochemistry VL - 41 IS - 17 N2 - Sequence alignment predicts that His(309) of pig heart NADP-dependent isocitrate dehydrogenase is equivalent to His(339) of the Escherichia coli enzyme, which interacts with the coenzyme in the crystal structure [Hurley et al. (1991) Biochemistry 30, 8671-8688], and porcine His(315) and His(319) are close to that site. The mutant porcine enzymes H309Q, H309F, H315Q, and H319Q were prepared by site-directed mutagenesis, expressed in E. coli, and purified. The H319Q mutant has K(m) values for NADP, isocitrate, and Mn(2+) similar to those of wild-type enzyme, and V(max) = 20.1, as compared to 37.8 micromol of NADPH min(-1) (mg of protein)(-1) for wild type. Thus, His(319) is not involved in coenzyme binding and has a minimal effect on catalysis. In contrast, H315Q exhibits a K(m) for NADP 40 times that of wild type and V(max) = 16.2 units/mg of protein, with K(m) values for isocitrate and Mn(2+) similar to those of wild type. These results implicate His(315) in the region of the NADP site. Replacement of His(309) by Q or F yields enzyme with no detectable activity. The His(309) mutants bind NADPH poorly, under conditions in which wild type and H319Q bind 1.0 mol of NADPH/mol of subunit, indicating that His(309) is important for the binding of coenzyme. The His(309) mutants bind isocitrate stoichiometrically, as do wild-type and the other mutant enzymes. However, as distinguished from the wild-type enzyme, the His(309) mutants are not oxidatively cleaved by metal isocitrate, implying that the metal ion is not bound normally. Since circular dichroism spectra are similar for wild type, H315Q, and H319Q, these amino acid substitutions do not cause major conformational changes. In contrast, replacement of His(309) results in detectable change in the enzyme's CD spectrum and therefore in its secondary structure. We propose that His(309) plays a significant role in the binding of coenzyme, contributes to the proper coordination of divalent metal ion in the presence of isocitrate, and maintains the normal conformation of the enzyme. SN - 0006-2960 UR - https://www.unboundmedicine.com/medline/citation/11969425/Evaluation_by_mutagenesis_of_the_roles_of_His309_His315_and_His319_in_the_coenzyme_site_of_pig_heart_NADP_dependent_isocitrate_dehydrogenase_ DB - PRIME DP - Unbound Medicine ER -