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首页> 外文期刊>Journal of bacteriology >The “Intracellular” Poly(3-Hydroxybutyrate) (PHB) Depolymerase of Rhodospirillum rubrum Is a Periplasm-Located Protein with Specificity for Native PHB and with Structural Similarity to Extracellular PHB Depolymerases
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The “Intracellular” Poly(3-Hydroxybutyrate) (PHB) Depolymerase of Rhodospirillum rubrum Is a Periplasm-Located Protein with Specificity for Native PHB and with Structural Similarity to Extracellular PHB Depolymerases

机译：红螺螺旋藻的“细胞内”聚（3-羟基丁酸）（PHB）解聚酶是一种定位于周质的蛋白，对天然PHB具有特异性，并且与细胞外PHB解聚酶具有结构相似性

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Rhodospirillum rubrum possesses a putative intracellular poly(3-hydroxybutyrate) (PHB) depolymerase system consisting of a soluble PHB depolymerase, a heat-stable activator, and a 3-hydroxybutyrate dimer hydrolase (J. M. Merrick and M. Doudoroff, J. Bacteriol. >88:60-71, 1964). In this study we reinvestigated the soluble R. rubrum PHB depolymerase (PhaZ1). It turned out that PhaZ1 is a novel type of PHB depolymerase with unique properties. Purified PhaZ1 was specific for amorphous short-chain-length polyhydroxyalkanoates (PHA) such as native PHB, artificial PHB, and oligomer esters of (R)-3-hydroxybutyrate with 3 or more 3-hydroxybutyrate units. Atactic PHB, (S)-3-hydroxybutyrate oligomers, medium-chain-length PHA, and lipase substrates (triolein, tributyrin) were not hydrolyzed. The PHB depolymerase structural gene (phaZ1) was cloned. Its deduced amino acid sequence (37,704 Da) had no significant similarity to those of intracellular PHB depolymerases of Wautersia eutropha or of other PHB-accumulating bacteria. PhaZ1 was found to have strong amino acid homology with type-II catalytic domains of extracellular PHB depolymerases, and Ser42, Asp138, and His178 were identified as catalytic-triad amino acids, with Ser42 as the putative active site. Surprisingly, the first 23 amino acids of the PHB depolymerase previously assumed to be intracellular revealed features of classical signal peptides, and Edman sequencing of purified PhaZ1 confirmed the functionality of the predicted cleavage site. Extracellular PHB depolymerase activity was absent, and analysis of cell fractions unequivocally showed that PhaZ1 is a periplasm-located enzyme. The previously assumed intracellular activator/depolymerase system is unlikely to have a physiological function in PHB mobilization in vivo. A second gene, encoding the putative true intracellular PHB depolymerase (PhaZ2), was identified in the genome sequence of R. rubrum.
机译： Rhodospirillum rubrum 具有推定的细胞内聚3-羟基丁酸酯（PHB）解聚酶系统，该系统由可溶性PHB解聚酶，热稳定活化剂和3-羟基丁酸酯二聚水解酶组成（JM Merrick和M. Doudoroff，J. Bacteriol。> 88： 60-71，1964年）。在这项研究中，我们重新研究了可溶性 R。风疹PHB解聚酶（PhaZ1）。事实证明，PhaZ1是一种新型的具有独特特性的PHB解聚酶。纯化的PhaZ1专用于无定形短链多羟基链烷酸酯（PHA），例如天然PHB，人工PHB和具有3个或更多个3-羟基丁酸酯单元的（ R ）-3-羟基丁酸酯的低聚物酯。 Atactic PHB，（ S ）-3-羟基丁酸酯低聚物，中链长度的PHA和脂肪酶底物（三油精，三丁酸甘油酯）未水解。克隆了PHB解聚酶的结构基因（ phaZ1 ）。其推导的氨基酸序列（37704 Da）与 Wautersia eutropha 或其他积累PHB的细菌的细胞内PHB解聚酶没有明显相似性。发现PhaZ1与细胞外PHB解聚酶的II型催化结构域以及Ser 42 ，Asp 138 和His 178 具有很强的氨基酸同源性。 >被认为是催化三元组氨基酸，Ser 42 是假定的活性位点。出乎意料的是，以前被认为是细胞内PHB解聚酶的前23个氨基酸揭示了经典信号肽的特征，纯化的PhaZ1的Edman测序证实了预测的切割位点的功能。细胞外PHB解聚酶活性不存在，并且对细胞组分的分析明确显示，PhaZ1是周质定位的酶。先前假定的细胞内激活剂/解聚酶系统不太可能在体内PHB动员中具有生理功能。在 R的基因组序列中鉴定出第二个编码推定的真正细胞​​内PHB解聚酶（PhaZ2）的基因。风疹。

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