Molecular evolution of tryptophan degrading enzymes.

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K07514
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Evolutionary biology
• Research Institution: Kochi University
• Principal Investigator: Yuasa Hajime 高知大学, 教育研究部自然科学系理工学部門, 准教授 (40322797)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: トリプトファン分解酵素 / 分子進化 / 比較生化学

Outline of Final Research Achievements

The ciliate Blepharisma has four IDO genes and each IDO enzyme has a distinct enzymatic property. IDO-III has a high affinity for L-Trp, whereas the affinity of the other isoforms for L-Trp is low. Meanwhile, IDO-I shows a significant catalytic activity with another indole compound: 5-hydroxy-L-tryptophan. By analysing a series of chimeric enzymes based on extant and predicted ancestral enzymes, Asn131 in IDO-I and Glu132 in IDO-III were identified as the key residues responsible for their high affinity for each specific substrate.
The invertebrate IDOs generally show low catalytic efficiency for L-Trp. Meanwhile, two IDO isoforms from scallop (IDO-I and -III) and sponge IDOs show high L-Trp catalytic activity, which is comparable to vertebrate IDO1. Site-directed mutagenesis experiments have revealed that two residues, Tyr located at the 2nd residue on the F-helix (F2nd) and His located at G9th, are crucial for the high catalytic efficiency of these high performance invertebrate IDOs.

Free Research Field

分子進化

Academic Significance and Societal Importance of the Research Achievements

繊毛虫BlepharismaのIDO-IはL-トリプトファン以外のインドール化合物に，より高い親和性を示す点で，他に例の無いIDOである。その基質特異性に関わるアミノ酸残基を特定（Asn131）したことは，IDOの分子進化を探る上で重要である。更に，予想祖先型配列のキメラ解析への応用が有効な手段であることも証明できた。また，IDOの高触媒効率化において，脊椎・無脊椎動物に共通してF2nd/G9thの2つの残基が重要であることが判明し，今後のトリプトファン分解酵素の研究発展に対し，重要な情報となると考えられる。