Studies on inhibition of respiratory cytochrome bc1 complex by the fungicide pyrimorph suggest a novel inhibitory mechanism.
The respiratory chain cytochrome bc1 complex (cyt bc1) is a major target of numerous antibiotics and fungicides. All cyt bc1 inhibitors act on either the ubiquinol oxidation (QP) or ubiquinone reduction (QN) site. The primary cause of resistance to bc1 inhibitors is target site mutations, creating a need for novel agents that act on alternative sites within the cyt bc1 to overcome resistance. Pyrimorph, a synthetic fungicide, inhibits the growth of a broad range of plant pathogenic fungi, though little is known concerning its mechanism of action. In this study, using isolated mitochondria from pathogenic fungus Phytophthora capsici, we show that pyrimorph blocks mitochondrial electron transport by affecting the function of cyt bc1. Indeed, pyrimorph inhibits the activities of both purified 11-subunit mitochondrial and 4-subunit bacterial bc1 with IC50 values of 85.0 μM and 69.2 μM, respectively, indicating that it targets the essential subunits of cyt bc1 complexes. Using an array of biochemical and spectral methods, we show that pyrimorph acts on an area near the QP site and falls into the category of a mixed-type, noncompetitive inhibitor with respect to the substrate ubiquinol. In silico molecular docking of pyrimorph to cyt b from mammalian and bacterial sources also suggests that pyrimorph binds in the vicinity of the quinol oxidation site.
Department of Applied Chemistry, China Agricultural University, Beijing, China; Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America.
Yu-Mei
YM
Xiao
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America.
Lothar
L
Esser
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America.
Fei
F
Zhou
Department of Applied Chemistry, China Agricultural University, Beijing, China.
Chang
C
Li
Department of Applied Chemistry, China Agricultural University, Beijing, China; Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America.
Yi-Hui
YH
Zhou
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma, United States of America.
Chang-An
CA
Yu
Department of Applied Chemistry, China Agricultural University, Beijing, China.
Zhao-Hai
ZH
Qin
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America.
Di
D
Xia
D000178:Acrylamides / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D004579:Electron Transport / Q000187:drug effects; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology*
D000178:Acrylamides; D005659:Fungicides, Industrial; D009025:Morpholines; C550850:pyrimorph; D014450:Electron Transport Complex III