Structural analysis of pathogenic and nonpathogenic polygalacturonases by synchrotron radiation

Research Project

Project/Area Number	16K07619
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Plant protection science
Research Institution	Kagoshima University
Principal Investigator	Nakamura Masayuki 鹿児島大学, 農水産獣医学域農学系, 准教授 (90404475)
Research Collaborator	Fujita Kiyotaka Minami Yuji
Project Period (FY)	2016-10-21 – 2019-03-31
Project Status	Completed (Fiscal Year 2018)
Budget Amount *help	¥4,810,000 (Direct Cost: ¥3,700,000、Indirect Cost: ¥1,110,000) Fiscal Year 2018: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000) Fiscal Year 2017: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000) Fiscal Year 2016: ¥2,990,000 (Direct Cost: ¥2,300,000、Indirect Cost: ¥690,000)
Keywords	ポリガラクツロナーゼ / 病原性 / 立体構造 / 糸状菌 / ペクチン / プロトペクチナーゼ / タンパク質発現 / タンパク質立体構造
Outline of Final Research Achievements	Geotrichum candidum causes soft rot which is an important cause of postharvest losses of citrus fruits in the world. There are both pathogenic and nonpathogenic isolates in the fungus. A polygalacturonase (PG), one of pectic enzymes, from the pathogenic isolates is a key factor to pathogenicity. However, the nonpathogenic isolates also have PGs. In this research, the pathogenesis of PGs was analyzed structurally using S31PG1 from the pathogenic isolate and S63PG1 from the nonpathogenic isolate. As a result, the structure of their active site clefts is crucial to pathogenicity and the specificity of the cleft structure to pathogenicity is not determined in a certain region but dictated by the whole region of the cleft. These results suggest that the cleft structure involved in pathogenicity was likely created accidentally, leading to the ability to act on complex substrates for pathogenesis, and the difference between the pathogenic and the nonpathogenic isolates of the fungus.
Academic Significance and Societal Importance of the Research Achievements	これまで、植物病原菌の保持するペクチン分解酵素のポリガラクツロナーゼ(PG)は、病原微生物だけでなく、有用微生物や植物自体にも存在していたことから、PGと病原性との関わりについては、不明な点が多かった。しかし、本研究により、PGが病原性を獲得する場合の原因は、基質結合部位の溝(クレフト)が、植物組織内に存在している高分子ペクチンに対し、ある特定の共通した構造で対応している訳ではなく、構造の異なるペクチンそれぞれに対し、クレフト全体で奇跡的に偶然対応していることが明らかとなった。以上の結果は、学術上意義が高いだけなく、新たな病害防除の確立にもつながる基礎的成果となった。