Structural Insights on PHA Binding Protein PhaP from Aeromonas hydrophila

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Phasins (PhaPs) are amphiphilic proteins associated with microbial polyhydroxyalkanoate (PHA) granules.
• They play roles in PHA accumulation, protein folding, and granule structure, but their molecular functions remain unclear due to limited structural data.

Purpose of the Study:

• To elucidate the structural basis of PhaP function by determining the crystal structure of PhaP from Aeromonas hydrophila (PhaP_Ah).
• To investigate the structure-function relationship of PhaP_Ah and engineer improved variants.

Main Methods:

• X-ray crystallography was used to determine the three-dimensional structure of PhaP_Ah.
• Biochemical assays were performed to assess the stability and emulsification properties of wild-type and mutant PhaP_Ah.

Main Results:

• The crystal structure revealed PhaP_Ah as a tetramer with an 8 α-helical coiled-coil structure.
• Each monomer exhibits distinct hydrophobic and hydrophilic surfaces, explaining its surfactant properties.
• Mutagenesis studies identified key residues enhancing protein stability and emulsification.

Conclusions:

• The determined PhaP_Ah structure provides the first atomic-level insight into phasin structure and function.
• This structural knowledge is vital for understanding PHA biosynthesis in vivo and the unique surfactant capabilities of PhaPs.
• The findings facilitate the exploration of PhaPs for biotechnological applications, such as bio-surfactants and amphipathic coatings.