Six types of proteins constitute the proteinaceous PHB surface layer in R. eutropha: (i) the PHB synthase (PhaC1) is the key enzyme of PHB synthesis and catalyses the polymerization process of 3-hydroxybutyryl-CoA provided by the central metabolism [9, 17, 18]. The function of a second – catalytically inactive – PHB synthase, PhaC2 [2] is unknown. However, PhaC2 principally has the capacity to bind to PHB granules in vivo [19]; (ii) phasin proteins (PhaPs), in particular PhaP1, cover
most parts of the granule surface and prevent Repotrectinib datasheet coalescence of granules [20–23]; (iii) PHB depolymerases (PhaZs) are important for reutilization (mobilization) of the polymer during times of starvation [24–28]; (iv) oligomer hydrolases (PhaZb, PhaZc, alternative designation PhaYs) are involved in cleavage of intermediately formed 3-hydroxybutyrate (3HB) oligomers during mobilization
[29]; (v) regulatory proteins (PhaRs) regulate expression of selected phasin genes [30, 31] and (vi) Selleckchem AR-13324 PhaM represents the prototype of a recently discovered novel type of PHB granule associated protein that has phasin properties but also can bind to DNA [32]. However, despite this considerable amount of knowledge it is still an open question whether PHB granules are formed randomly within the cytoplasm or whether localization of PHB granules is controlled by the bacteria. Several studies using fluorescence microscopy (FM) [33–35] and transmission electron microscopy (TEM) [36, 37] were performed in the last decade 3-oxoacyl-(acyl-carrier-protein) reductase to address this question. However, the results of these
studies were inconsistent. While FM analysis of PHB granule formation in different PHB accumulating species suggested a non random localization of “early” PHB granules in the cell periphery of these species [14, 33, 34], investigation of PHB granule formation in R. eutropha by TEM suggested that PHB granules are formed predominantly in the cell centre near dark stained “learn more mediation elements” [36, 37]. Electron cryotomography recently revealed that in R. eutropha PHB granules at different stages of PHB accumulation are localized more or less in the cell center whereas a preferential formation of PHB granules in the cell periphery has not been observed [38]. The reason why FM and TEM resulted in apparently contradicting results remained unclear although the studies were performed with the same wild type strain. In recent studies of our laboratory we showed that PhaM can bind to PHB, to phasin PhaP5, to PHB synthase PhaC1 and to DNA [22, 32]. Consequently, we decided to reinvestigate PHB granule formation and intracellular localization in R. eutropha wild type and in mutants with altered expression of PhaP5 or PhaM.