Structural and functional characterization of a thermostable secretory phospholipase A₂ from Sciscionella marina and its application in liposome biotransformation

Secretory phospholipase A₂ (sPLA₂), which hydrolyzes the sn-2 acyl bond of lecithin in a Ca²⁺-dependent manner, is an important enzyme in the oil and oleochemical industries. However, most sPLA₂s are not stable under process conditions. Therefore, a thermostable sPLA₂ was investigated in this study. A marine bacterial sPLA₂ isolated from Sciscionella marina (Sm-sPLA₂) 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 sPLA₂ (i.e. sPLA₂ from Streptomyces violaceoruber; Sv-sPLA₂). Consistent with this, the melting temperature of Sm-sPLA₂ was measured to be 7.7°C higher than that of Sv-sPLA₂. Furthermore, Sm-sPLA₂ exhibited an improved biotransformation performance compared with Sv-sPLA₂ 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 Ca²⁺-binding loop into the rest of the protein body is directly linked to the thermal stability of Sm-sPLA₂. This finding provides a novel structural insight into the thermostability of sPLA₂ and could be applied to create mutant proteins with enhanced industrial potential.