Characteristics of phospholipase A2 mutant of the starfish Asterina pectinifera

Site-directed mutagenesis study of phospholipase A2 (PLA2) from the pyloric ceca of starfish Asterina pectinifera was used to probe the relationship between polar-group specificity and structure of the pancreatic loop region. The sequence of the cDNA encoding the starfish PLA2 was exchanged by the oligonucleotide-directed dual amber-long and accurate polymerase chain reaction method to insert Lys residue between Cys-62 and Gly-63. The modified cDNA was inserted into the expression plasmid pET-16b, and PLA2 mutant was expressed in Escherichia coli Origami™ B (DE3) by induction with isopropyl-beta-d(−)-thiogalactopyranoside. The starfish PLA2 mutant showed essentially the same properties as the starfish native PLA2 with respect to substrate positional specificity, optimum pH, optimum temperature, Ca2+ requirement, and sodium deoxycholate requirement. However, the specific activity of the starfish PLA2 mutant for egg yolk PC (950 U/mg) was extremely lower than that of native PLA2 (119,000 U/mg), but close to that of porcine pancreatic PLA2 (4300 U/mg). Moreover, the ratio of specific activity of the PLA2 mutant for phosphatidylcholine to phosphatidylethanolamine (98 times) was highly lower than that of native PLA2 (2650 times), but similar to that of porcine pancreatic PLA2 (25 times). Therefore, it was suggested that the charge and structure of pancreatic loop region of the starfish PLA2 might carry out important role on polar-group specificity.