Abstract

Phasins are proteins that are normally associated with granules of poly(3-hydroxybutyrate) (PHB), a biodegradable polymer accumulated by many bacteria as a reserve molecule. These proteins play an important role in the formation of the granules and are involved in regulatory functions. Phasins have been shown to enhance growth and polymer production in natural and recombinant PHB producers. PhaP from Azotobacter sp. FA-8 enhances growth and polymer in PHB producing Escherichia coli, and it was also observed to have an unexpected protective effect in a non PHB producing E. coli strain, resulting in increased growth and higher resistance to stress conditions, such as heat and oxidation. These observations suggested that PhaP could act as a chaperone. In order to characterize this protein and shed light on its possible mechanism of action, it was purified and submitted to further studies to determine its structure and analyze its putative role as a chaperone. PhaP was observed to protect the model substrate citrate synthase in thermal and chemical denaturation experiments. Its interaction with inclusion body forming overexpressed recombinant proteins was also investigated. These results open the door to novel biotechnological applications for this protein, for example, in the production of recombinant proteins and other heterologous products in E. coli.