Investigation of biosynthetic mechanism of cyclic tetrapyrrole: Construction and cyclization of hydroxymethylbilane

2017 Fiscal Year Final Research Report

• Project/Area Number: 15K07018
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Functional biochemistry
• Research Institution: Kurume University
• Principal Investigator: SATO Hideaki 久留米大学, 医学部, 准教授 (60271996)
• Co-Investigator(Kenkyū-buntansha): 東元 祐一郎 久留米大学, 医学部, 教授 (40352124) ; 杉島 正一 久留米大学, 医学部, 准教授 (30379292) ; 原田 二朗 久留米大学, 医学部, 講師 (10373094) ; 塚口 舞 (古澤舞) 久留米大学, 医学部, 助教 (40624094)
• Project Period (FY): 2015-04-01 – 2018-03-31
• Keywords: ヘム生合成 / ポルフィリン生合成 / テトラピロール / Ｘ線結晶構造解析 / 酵素反応機構

Outline of Final Research Achievements

We tried to clarify the reaction mechanism of the two enzymes involved in the construction and cyclization of tetrapyrrole, based on their crystal structure. In particular, hydroxymethylbilane synthase (HMBS) has a dipyrromethane cofactor and combines four molecules of porphobilinogen as substrates sequentially to form a linear tetrapyrrole, hydroxymethylbilane. We separated enzyme-substrates complexes depending on the number of bound substrates, and succeeded in X-ray crystal structure analysis of HMBS in complex with two substrate molecules. In its crystal structure, compared to the holo form with no substrate, the cofactor moved to the far side of the active site and the two substrate molecules located in the space where originally occupied by the cofactor. These results indicate that the active site of HMBS changes its conformation greatly during the tetrapyrrole construction from substrates.

Free Research Field

ヘム関連酵素の生化学