PhaP

PhaP is a phasin protein that coats polyhydroxyalkanoate (PHA) granules in bacteria. The term PhaP refers to a family of granule-associated proteins encoded by phaP genes and is best studied in Cupriavidus necator (formerly Ralstonia eutropha).

Function and role: Phasin proteins bind to PHB granules, stabilizing them and regulating their size and number. Their expression can influence the overall amount and intracellular distribution of PHAs. They may interact with PHA synthase (PhaC) or other regulatory factors to coordinate granule formation and maintenance.

Genetics and regulation: In C. necator, phaP is part of a regulatory network that includes phaR, a transcriptional regulator that binds PHB granules and represses phaP transcription in PHB-free conditions. Under PHB-accumulating conditions, PhaR associations change, permitting phaP expression. Some bacteria possess multiple phaP genes, encoding distinct phasins with potentially different granule-binding properties.

Structure and properties: Phasin proteins are typically around 20–30 kDa and possess amphipathic helices that mediate binding to the hydrophobic PHB surface. They are generally peripheral to the granule and do not exhibit enzymatic activity.

Applications and uses: The localization of PhaP to PHB granules makes it a useful platform for surface display of enzymes, antigens, or other proteins on granules. This strategy is explored in metabolic engineering and biotechnology to create stable, granule-associated biocatalysts or materials.

See also: Polyhydroxyalkanoates, PHA synthase (PhaC), PHA granule, PhaR.