Dataset Information

Haloarchaeal-type ?-ketothiolases involved in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesis in Haloferax mediterranei.

ABSTRACT: The key enzymes for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biosynthesis in haloarchaea have been identified except the ?-ketothiolase(s), which condense two acetyl coenzyme A (acetyl-CoA) molecules to acetoacetyl-CoA, or one acetyl-CoA and one propionyl-CoA to 3-ketovaleryl-CoA. Whole-genome analysis has revealed eight potential ?-ketothiolase genes in the haloarchaeon Haloferax mediterranei, among which the PHBV-specific BktB and PhaA were identified by gene knockout and complementation analysis. Unlike all known bacterial counterparts encoded by a single gene, the haloarchaeal PhaA that was involved in acetoacetyl-CoA generation, was composed of two different types of subunits (PhaA? and PhaA?) and encoded by the cotranscribed HFX_1023 (phaA?) and HFX_1022 (phaA?) genes. Similarly, the BktB that was involved in generation of acetoacetyl-CoA and 3-ketovaleryl-CoA, was also composed of two different types of subunits (BktB? and BktB?) and encoded by cotranscribed HFX_6004 (bktB?) and HFX_6003 (bktB?). BktB? and PhaA? were the catalytic subunits and determined substrate specificities of BktB and PhaA, respectively. Their catalytic triad "Ser-His-His" was distinct from the bacterial "Cys-His-Cys." BktB? and PhaA? both contained an oligosaccharide-binding fold domain, which was essential for the ?-ketothiolase activity. Interestingly, BktB? and PhaA? were functionally interchangeable, although PhaA? preferred functioning with PhaA?. In addition, BktB showed biotechnological potential for the production of PHBV with the desired 3-hydroxyvalerate fraction in haloarchaea. This is the first report of the haloarchaeal type of PHBV-specific ?-ketothiolases, which are distinct from their bacterial counterparts in both subunit composition and catalytic residues.

SUBMITTER: Hou J

PROVIDER: S-EPMC3753943 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Haloarchaeal-type β-ketothiolases involved in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesis in Haloferax mediterranei.

Hou Jing J Feng Bo B Han Jing J Liu Hailong H Zhao Dahe D Zhou Jian J Xiang Hua H

Applied and environmental microbiology 20130621 17

The key enzymes for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biosynthesis in haloarchaea have been identified except the β-ketothiolase(s), which condense two acetyl coenzyme A (acetyl-CoA) molecules to acetoacetyl-CoA, or one acetyl-CoA and one propionyl-CoA to 3-ketovaleryl-CoA. Whole-genome analysis has revealed eight potential β-ketothiolase genes in the haloarchaeon Haloferax mediterranei, among which the PHBV-specific BktB and PhaA were identified by gene knockout and complement ...[more]

PMID: 23793631

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Project description:The effect of accelerated weathering on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV-based nanocomposites with rutile titanium (IV) dioxide (PHBV/TiO2) was investigated. The accelerated weathering test applied consecutive steps of UV irradiation (at 340 nm and 0.76 W m-2 irradiance) and moisture at 50 °C following the ASTM D4329 standard for up to 2000 h of exposure time. The morphology, chemical structure, crystallization, as well as the mechanical and thermal properties were studied. Samples were characterized after 500, 1000, and 2000 h of exposure time. Different degradation mechanisms were proposed to occur during the weathering exposure and were confirmed based on the experimental data. The PHBV surface revealed cracks and increasing roughness with the increasing exposure time, whereas the PHBV/TiO2 nanocomposites showed surface changes only after 2000 h of accelerated weathering. The degradation of neat PHBV under moisture and UV exposure occurred preferentially in the amorphous phase. In contrast, the presence of TiO2 in the nanocomposites retarded this process, but the degradation would occur simultaneously in both the amorphous and crystalline segments of the polymer after long exposure times. The thermal stability, as well as the temperature and rate of crystallization, decreased in the absence of TiO2. TiO2 not only provided UV protection, but also restricted the physical mobility of the polymer chains, acting as a nucleating agent during the crystallization process. It also slowed down the decrease in mechanical properties. The mechanical properties were shown to gradually decrease for the PHBV/TiO2 nanocomposites, whereas a sharp drop was observed for the neat PHBV after an accelerated weathering exposure. Atomic force microscopy (AFM), using the amplitude modulation-frequency modulation (AM-FM) tool, also confirmed the mechanical changes in the surface area of the PHBV and PHBV/TiO2 samples after accelerated weathering exposure. The changes in the physical and chemical properties of PHBV/TiO2 confirm the barrier activity of TiO2 for weathering attack and its retardation of the degradation process.

Dataset Information

Haloarchaeal-type ?-ketothiolases involved in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesis in Haloferax mediterranei.

Publications

Haloarchaeal-type β-ketothiolases involved in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesis in Haloferax mediterranei.

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