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

Secretory phospholipase A (sPLA), which hydrolyzes the sn-2 acyl bond of lecithin in a Ca-dependent manner, is an important enzyme in the oil and oleochemical industries. However, most sPLAs are not stable under process conditions. Therefore, a thermostable sPLA was investigated in this study. A marine bacterial sPLA isolated from Sciscionella marina (Sm-sPLA) 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 (i.e. sPLA from Streptomyces violaceoruber; Sv-sPLA). Consistent with this, the melting temperature of Sm-sPLA was measured to be 7.7°C higher than that of Sv-sPLA. Furthermore, Sm-sPLA exhibited an improved biotransformation performance compared with Sv-sPLA 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-binding loop into the rest of the protein body is directly linked to the thermal stability of Sm-sPLA. This finding provides a novel structural insight into the thermostability of sPLA and could be applied to create mutant proteins with enhanced industrial potential.