Steinbuchel A, Aerts K, Babel W, Follner C, Liebergesell M, Madkour M H, Mayer F, Pieper-Furst U, Pries A, Valentin H E
Institut fur Mikrobiologie der Westfalischen Wilhelms-Universitat Munster, Germany.
Can J Microbiol. 1995;41 Suppl 1:94-105. doi: 10.1139/m95-175.
Some mathematical calculations were done that provided information about the structure and biochemistry of polyhydroxyalkanoic acid (PHA) granules and about the amounts of the different constituents that contribute to the PHA granules. The data obtained from these calculations are compared with data from the literature, which show that PHA granules consist not only of the polyester but also of phospholipids and proteins. The latter are referred to as granule-associated proteins, and they are always located at the surface of the PHA granules. A concept is proposed that distinguishes four classes of structurally and functionally different granule-associated proteins: (i) class I comprises the PHA synthases, which catalyze the formation of ester linkages between the constituents; (ii) class II comprises the PHA depolymerases, which are responsible for the intracellular degradation of PHA, (iii) class III comprises a new type of protein, which is referred to as phasins and which has most probably a function analogous to that of oleosins in oilseed plants, and (iv) class IV comprises all other proteins, which have been found to be associated with the granules but do not belong to classes I-III. Particular emphasis is placed on the phasins, which constitute a significant fraction of the total cellular protein. Phasins are assumed to form a close protein layer at the surface of the granules, providing the interface between the hydrophilic cytoplasm and the much more hydrophobic core of the PHA inclusion.
进行了一些数学计算，这些计算提供了有关聚羟基脂肪酸酯（PHA）颗粒的结构和生物化学以及构成PHA颗粒的不同成分数量的信息。将从这些计算中获得的数据与文献数据进行比较，文献数据表明PHA颗粒不仅由聚酯组成，还由磷脂和蛋白质组成。后者被称为颗粒相关蛋白，它们总是位于PHA颗粒的表面。提出了一个概念，该概念区分了四类结构和功能不同的颗粒相关蛋白：（i）I类包括PHA合酶，其催化成分之间酯键的形成；（ii）II类包括PHA解聚酶，其负责PHA的细胞内降解；（iii）III类包括一种新型蛋白质，称为phasins，其功能很可能类似于油料植物中的油质蛋白；（iv）IV类包括所有其他已发现与颗粒相关但不属于I-III类的蛋白质。特别强调phasins，它们占细胞总蛋白的很大一部分。假定phasins在颗粒表面形成紧密的蛋白质层，在亲水性细胞质和PHA内含物的疏水性更强的核心之间提供界面。
