Phasins: small but crafty

DANIELA ALVAREZ; M. JULIA PETINARI; MARIELA MEZZINA; PABLO NIKEL; DIANA E WETZLER

Madrid

Simposio; 15th international Symposium of Biopolymers; 2016

Phasins are small proteins associated to intracellular polyhydroxyalkanoate (PHA) granules, a biodegradable polymer accumulated by many bacteria under unfavorable conditions as a carbon and energy reserve compound. Phasins not only play an important structural role in  polymer accumulation and the number and size of the granules, but have also been shown to have other roles, such as regulatory functions. Expression of a phasin from Azotobacter sp. FA8 (PhaPAz) has a protective effect both in PHA-producing and non-PHA producing E. colistrains, evidenced in the increased growth and higher resistance to heat shock and superoxide stress. The effect described for this phasin is not only passive but involves an active role in promoting protein folding, and preventing unfolding due to its chaperone-like function. The protective effect observed for PhaPAz could be a common feature among phasins. To help elucidate this, we studied the effect of the expression of phasin PhbP from Pseudomonas extremoaustralis (PhbPPe) in recombinant E. coli. An in silico comparative analysis of PhaPAzand PhbPPe revealed that both phasins have similar secondary structures, consisting of α-helices and random coil regions. The protective effect of PhbPPe was studied by analyzing the level of expression of the small heat shock protein IbpA, which is a stress indicator. The chaperone properties of this phasin were also studied in vitro testing its capability to protect the model protein citrate synthase from thermal denaturation. As previously observed for PhaPAz, PhbPPe was observed to decrease heat shock protein induction, and to protect citrate synthase from denaturation. These results show that both phasins have similar protective properties that could be potentially useful for a number of applications. As chaperones have been shown to be able to increase solvent tolerance, we analyzed the effect of PhaPAz on E.coli grown in the presence of several solvents. Expression of the phasin increased tolerance of E.coli to ethanol, butanol and 1,3 propanediol.  The effect of the phasin was also analyzed in ethanol producing E. coli, in which it was observed to cause an increase in the amount of ethanol produced. These results open the road for new possible applications of these small but multifacetic proteins