Structural and functional characterization of a thermostable secretory phospholipase A 2 from Sciscionella marina and its application in liposome biotransformation.

Secretory phospholipase A 2 (sPLA 2 ), which hydrolyzes the sn-2 acyl bond of lecithin in a Ca 2+ -dependent manner, is an important enzyme in the oil and oleochemical industries. However, most sPLA 2 s are not stable under process conditions. Therefore, a thermostable sPLA 2 was investigated in this study. A marine bacterial sPLA 2 isolated from Sciscionella marina (Sm-sPLA 2 ) was catalytically active even after 5 h of incubation at high temperatures of up to 50°C, which is outstanding compared with a representative bacterial sPLA 2 (i.e. sPLA 2 from Streptomyces violaceoruber; Sv-sPLA 2 ). Consistent with this, the melting temperature of Sm-sPLA 2 was measured to be 7.7°C higher than that of Sv-sPLA 2 . Furthermore, Sm-sPLA 2 exhibited an improved biotransformation performance compared with Sv-sPLA 2 in the hydrolysis of soy lecithin to lysolecithin and free fatty acids at 50°C. Structural and mutagenesis studies revealed that the Trp41-mediated anchoring of a Ca 2+ -binding loop into the rest of the protein body is directly linked to the thermal stability of Sm-sPLA 2 . This finding provides a novel structural insight into the thermostability of sPLA 2 and could be applied to create mutant proteins with enhanced industrial potential.