title: Identification of the haloarchaeal phasin (PhaP) that functions in polyhydroxyalkanoate accumulation and granule formation in Haloferax mediterranei.
abstract: The polyhydroxyalkanoate (PHA) granule-associated proteins (PGAPs) are important for PHA synthesis and granule formation, but currently little is known about the haloarchaeal PGAPs. This study focused on the identification and functional analysis of the PGAPs in the haloarchaeon Haloferax mediterranei. These PGAPs were visualized with two-dimensional gel electrophoresis (2-DE) and identified by matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry (MALDI-TOF/TOF MS). The most abundant protein on the granules was identified as a hypothetical protein, designated PhaP. A genome-wide analysis revealed that the phaP gene is located upstream of the previously identified phaEC genes. Through an integrative approach of gene knockout/complementation and fermentation analyses, we demonstrated that this PhaP is involved in PHA accumulation. The ΔphaP mutant was defective in both PHA biosynthesis and cell growth compared to the wild-type strain. Additionally, transmission electron microscopy results indicated that the number of PHA granules in the ΔphaP mutant cells was significantly lower, and in most of the ΔphaP cells only a single large granule was observed. These results demonstrated that the H. mediterranei PhaP was the predominant structure protein (phasin) on the PHA granules involved in PHA accumulation and granule formation. In addition, BLASTp and phylogenetic results indicate that this type of PhaP is exclusively conserved in haloarchaea, implying that it is a representative of the haloarchaeal type PHA phasin.
authors.affiliation: State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, People’s Republic of China.
authors.forename: Shuangfeng
authors.initials: S
authors.lastname: Cai
authors.forename: Lei
authors.initials: L
authors.lastname: Cai
authors.forename: Hailong
authors.initials: H
authors.lastname: Liu
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Liu
authors.forename: Jing
authors.initials: J
authors.lastname: Han
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Hua
authors.initials: H
authors.lastname: Xiang
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D019641:DNA, Archaeal / Q000737:chemistry / Q000235:genetics; D015180:Electrophoresis, Gel, Two-Dimensional; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D019623:Haloferax mediterranei / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D037121:Plant Lectins / Q000235:genetics* / Q000378:metabolism*; D054813:Polyhydroxyalkanoates / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D037121:Plant Lectins; D054813:Polyhydroxyalkanoates; C008825:phasin