PHA Granule Formation

The PhaC is soluble in the cytoplasm when the cells do not accumulate PHB. The enzyme becomes particle bound upon the onset of PHB biosynthesis [18]. According to the micelle model of PHA granule formation and according to the mechanism of PHA formation (see below) the enzyme is covalently bound to the growing polyester chain. Therefore, the enzyme is found in most PHA-... 

Fig. 2.5 The two models of PHA granule formation in bacteria, a Micelle model and b Budding model. The irregular lines represent the polymer chains...

Jurasek, L., Marchessault, R. Polyhydroxyalkanoate (PHA) granule formation in Ralstonia. Appl. Microbiol. Biotechnol. 64, 611-617 (2004)... 

The non-covalently attached proteins are not vital for PHA granule formation, however, they serve various biological functions, for example, PHA granule structure, PHA biosynthesis gene regulation, and PHA mobilization. Yet, only the covalently attached polyester synthases possess all the inherent properties needed for PHA granule formation. 

Peters, V. and Rehm, B.H.A. (2005) In vivo monitoring of PHA granule formation using GFP-labeled PHA synthases. FEMS Microbiol Lett., 248, 93-100. 

Separation of PHASCL and PHAMCL into two separate granules within the same cell often seems to occur if two different PHA synthases with non-overlapping substrate ranges are present in the cell. Obviously, each type of PHA synthase participates separately in the initiation of micelle formation of nascent PHA granules, because only PHA molecules of similar structure, which remain bound to the PHA synthase protein, can contribute to the formation of a micelle. When the granules become larger, further PHA synthase molecules can only bind to the surface of the granules if they represent the same type of PHA synthase. 

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