A Phasin with Many Faces: Structural Insights on PhaP from Azotobacter sp. FA8

Abstract

Phasins are a group of proteins associated to granules of polyhydroxyalkanoates (PHAs). Apart from their structural role as part of the PHA granule cover, different structural and regulatory functions have been found associated to many of them, and several biotechnological applications have been developed using phasin protein fusions. Despite their remarkable functional diversity, the structure of these proteins has not been analyzed except in very few studies. PhaP from Azotobacter sp. FA8 (PhaPAz) is a representative of the prevailing type in the multifunctional phasin protein family. Previous work performed in our laboratory using this protein have demonstrated that it has some very peculiar characteristics, such as its stress protecting effects in recombinant Escherichia coli, both in the presence and absence of PHA. The aim of the present work was to perform a structural characterization of this protein, to shed light on its properties. Its aminoacid composition revealed that it lacks clear hydrophobic domains, a characteristic that appears to be common to most phasins, despite their lipid granule binding capacity. The secondary structure of this protein, consisting of α-helices and disordered regions, has a remarkable capacity to change according to its environment. Several experimental data support that it is a tetramer, probably due to interactions between coiled-coil regions. These structural features have also been detected in other phasins, and may be related to their functional diversity.

Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

“…Generally PHAs are accumulated as light-refracting discrete granules inside the cell (123,124). These PHA granules can be stained specifically with Sudan black B or light fluorescent stains Nile blue A and Nile red ( Figure 4) (65,68,71,125,126).…”

“…Among the proteins associated to PHA granules, phasins constitute a very diverse group are the most dominant proteins of relatively small molecular size (124,140,141). A few that have been studied in detail revealed that they are associated with a structural role of PHA granules and may have several functions such as coating, stabilizing granules as structural proteins by non-covalently attached to the polyester core of granules ( Figure 5) (30,135,142,143,144) or activating genes and/or enzymes involved in PHA synthesis (124). Phasins promote PHA biosynthesis and their copy number has impact on PHA granule size (143,144).…”

“…Phasins promote PHA biosynthesis and their copy number has impact on PHA granule size (143,144). Phasins are inhibiting individual granules from coalescing and agglutinating with other granules and acting as a barrier between the polymer and other cellular components (123,124,145). In phasins mutants of R. eutropha, the cells accumulate less PHB, and they possess only one single large granule because separate granules coagule due to the "nacked" surface if the hydrophobic PHA molecules get in contact ( Figure 4) (140,142,146).…”

Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins

“…Secondary-structure in silico predictions for phasins PhaP1 to PhaP4 from R. eutropha, PhaP1 from Ralstonia solanacearum, PhaP from Ralstonia metallidurans (17), PhaP Az (18), and PhaP Sp (12) revealed that these phasins have a high percentage (close to 90%) of amino acids in an ␣-helix conformation. This was found to be a general characteristic of phasins (18)(19)(20).…”

A New Player in the Biorefineries Field: Phasin PhaP Enhances Tolerance to Solvents and Boosts Ethanol and 1,3-Propanediol Synthesis in Escherichia coli

“…The same result was obtained when a plasmid expressing phaP was introduced in the cells, indicating that PhaP was able to complement the phenotypic effects caused by the groEL mutation in a manner similar to that for the GroELS protein. Although PhaP has no sequence or structure similarity to GroELS or to other chaperones (54), its capability to increase the tolerance of the groEL mutant to the chemicals tested further supports the possibility that this could be due to its chaperone-like properties.…”