Characterization of the biosynthetic gene cluster for the ribosomally synthesized cyclic peptide ustiloxin B in Aspergillus flavus.
Ustiloxin B is a secondary metabolite known to be produced by Ustilaginoidea virens. In our previous paper, we observed the production of this compound by Aspergillus flavus, and identified two A. flavus genes responsible for ustiloxin B biosynthesis (Umemura et al., 2013). The compound is a cyclic tetrapeptide of Tyr-Ala-Ile-Gly, whose tyrosine is modified with a non-protein coding amino acid, norvaline. Although its chemical structure strongly suggested that ustiloxin B is biosynthesized by a non-ribosomal peptide synthetase, in the present study, we observed its synthesis through a ribosomal peptide synthetic (RiPS) pathway by precise sequence analyses after experimental validation of the cluster. The cluster possessed a gene (AFLA_094980), termed ustA, whose translated product, UstA, contains a 16-fold repeated peptide embedding a tetrapeptide, Tyr-Ala-Ile-Gly, that is converted into the cyclic moiety of ustiloxin B. This result strongly suggests that ustiloxin B is biosynthesized through a RiPS pathway and that UstA provides the precursor peptide of the compound. The present work is the first characterization of RiPS in Ascomycetes and the entire RiPS gene cluster in fungi. Based on the sequence analyses, we also proposed a biosynthetic mechanism involving the entire gene cluster. Our finding indicates the possibility that a number of unidentified RiPSs exist in Ascomycetes as the biosynthetic genes of secondary metabolites, and that the feature of a highly repeated peptide sequence in UstA will greatly contribute to the discovery of additional RiPS.
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan. Electronic address: umemura-m@aist.go.jp.
Myco
M
Umemura
Computational Biology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 2-4-7 Aomi, Koto-ku, Tokyo 135-0064, Japan.
Nozomi
N
Nagano
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
Hideaki
H
Koike
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Jin
J
Kawano
Technology Research Association of Highly Efficient Gene Design, 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Tomoko
T
Ishii
Technology Research Association of Highly Efficient Gene Design, 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Yuki
Y
Miyamura
Technology Research Association of Highly Efficient Gene Design, 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Moto
M
Kikuchi
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Koichi
K
Tamano
Beltsville Agricultural Regional Research Center, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705, USA.
Jiujiang
J
Yu
Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-4-7 Aomi, Koto-ku, Tokyo 135-0064, Japan.
Kazuo
K
Shin-ya
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 17-2-1 Higashi-Nijo, Tsukisamu, Toyohira-ku, Sapporo, Hokkaido 062-8517, Japan.
Masayuki
M
Machida
D001231:Aspergillus flavus / Q000235:genetics*; D053898:Biosynthetic Pathways; D005800:Genes, Fungal / Q000502:physiology; D005810:Multigene Family; D010456:Peptides, Cyclic / Q000096:biosynthesis / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism*; D017422:Sequence Analysis, DNA
D010456:Peptides, Cyclic; C089077:ustiloxin B
Aspergillus flavus; Fungal secondary metabolite biosynthesis; Gene cluster; Ribosomal peptide synthesis; Ustiloxin B