Modelling of microbial polyhydroxyalkanoate surface binding protein PhaP for rational mutagenesis

Phasins are unusual amphiphilic proteins that bind to microbial polyhydroxyalkanoate (PHA) granules in nature and show great potential for various applications in biotechnology and medicine. Despite their remarkable diversity, only the crystal structure of PhaPAh from Aeromonas hydrophila has been solved to date. Based on the structure of PhaPAh , homology models of PhaPAz from Azotobacter sp. FA-8 and PhaPTD from Halomonas bluephagenesis TD were successfully established, allowing rational mutagenesis to be conducted to enhance the stability and surfactant properties of these proteins. PhaPAz mutants, including PhaPAz Q38L and PhaPAz Q78L, as well as PhaPTD mutants, including PhaPTD Q38M and PhaPTD Q72M, showed better emulsification properties and improved thermostability (6-10°C higher melting temperatures) compared with their wild-type homologues under the same conditions. Importantly, the established PhaP homology-modelling approach, based on the high-resolution structure of PhaPAh , can be generalized to facilitate the study of other PhaP members.