Elucidation of expression/regulation of genes involved in microbial polyhydroxylalkanoate (PHA)

为了阐明反硝化菌和甲基营养菌反硝化副球菌PHA合成/降解的调控机制，开展了基因/酶/代谢水平的研究，取得了以下成果： 1．在 phaP 的下游发现了一个名为 phaR 的基因，该基因编码 PHA 颗粒相关蛋白 phasin。 PhaR是一种转录因子，它结合phaP的启动子区域，也结合PHA颗粒。调节PHA颗粒的大小。2．参与PHA合成/降解的基因，即phaA、phaB、phaC和phaZ，几乎组成型表达，与PHA合成水平无关。代谢物辅酶A被提议作为PHA生物合成的全局调节因子。 3．纯化了参与 PHA 细胞内降解的三种酶，即两种不同的 PHA 解聚酶和 PHB 寡聚物水解酶，并阐明了它们的生化特性。其中一种 PHA 解聚酶是一种新型酶，可直接从 PHB 聚合物产生 3-羟基丁酸酯单体。

With aim of elucidating regulation mechanism of PHA synthesis/degradation within denitrifyer and methylotroph, Paracoccus denitrificans, studies were carried out on genes/enzymes/metabolism levels, and the following have been achieved.1. A gene named phaR, was discovered downstream of phaP that encoded PHA granule-associated protein, phasin. PhaR was a transcription factor which bound promoter region of phaP and also bound the PHA granule. It regulated the size of PHA granule.2. Genes involved in PHA synthesis/degradation, i.e phaA, phaB, phaC, and phaZ, were expressed almost constitutively irrespective of PHA synthesis level.A metabolite, Coenzyme A, was proposed as a global regulator of PHA biosynthesis.3. Three enzymes involved in the intracellular degradation of PHA, i.e. two different kinds of PHA depolymerases, and PHB oligomer hydrolase, were purified and their biochemical characteristics were elucidated. One of the PHA depolymerases was a novel enzyme which yielded 3-hydroxylbutyrate monomer directly from PHB polymer.