Two polymorphic forms of human histamine methyltransferase: Structural, thermal and kinetic comparisons

• Type of Material: Article
• Authors: John Horton, Emory University; Ken Sawada, Emory University; Masahiro Nishibori, Okayama University Medical School; Xing Zhang, Emory University; Xiaodong Cheng, Emory University
• Language: English
• Date: 2001-09-01
• Publisher: Elsevier (Cell Press)
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2001 Cell Press. Published by Elsevier Inc.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/S0969-2126(01)00643-8
• Title of Journal or Parent Work: Structure
• ISSN: 0969-2126
• Volume: 9
• Issue: 9
• Start Page: 837
• End Page: 849
• Grant/Funding Information: These studies were supported in part by the Emory University School of Medicine Department of Biochemistry start-up funds, the Georgia Research Alliance, the National Science Foundation INT-0003815, and the Japan Society for the Promotion of Science.
• Keywords: Science & Technology; PROTEIN; N-METHYLTRANSFERASE; antimalarial drug quinacrine; BRAIN; polymorphism; CATECHOL-O-METHYLTRANSFERASE; Cell Biology; thermal stability; PHARMACOGENETICS; Biophysics; H-1 RECEPTOR; methylation; PURIFICATION; histamine; RAT-KIDNEY; INHIBITION; 3-DIMENSIONAL STRUCTURE; Life Sciences & Biomedicine; Biochemistry & Molecular Biology
• Research Categories: Health Sciences, Pharmacology; Chemistry, Biochemistry; Health Sciences, General

Abstract

Background: Histamine plays important biological roles in cell-to-cell communication; it is a mediator in allergic responses, a regulator of gastric acid secretion, a messenger in bronchial asthma, and a neurotransmitter in the central nervous system. Histamine acts by binding to histamine receptors, and its local action is terminated primarily by methylation. Human histamine N-methyltransferase (HNMT) has a common polymorphism at residue 105 that correlates with the high- (Thr) and low- (Ile) activity phenotypes. Results: Two ternary structures of human HNMT have been determined: the Thr105 variant complexed with its substrate histamine and reaction product AdoHcy and the Ile105 variant complexed with an inhibitor (quinacrine) and AdoHcy. Our steady-state kinetic data indicate that the recombinant Ile105 variant shows 1.8- and 1.3-fold increases in the apparent KM for AdoMet and histamine, respectively, and slightly (16%) but consistently lower specific activity as compared to that of the Thr105 variant. These differences hold over a temperature range of 25°C-45°C in vitro. Only at a temperature of 50°C or higher is the Ile105 variant more thermolabile than the Thr105 enzyme. Conclusions: HNMT has a 2 domain structure including a consensus AdoMet binding domain, where the residue 105 is located on the surface, consistent with the kinetic data that the polymorphism does not affect overall protein stability at physiological temperatures but lowers KM values for AdoMet and histamine. The interactions between HNMT and quinacrine provide the first structural insights into a large group of pharmacologic HNMT inhibitors and their mechanisms of inhibition.