Structural variations and phospholipid binding characteristics of Streptomyces klenkii phospholipase D at the lipid-water interface

The lack of knowledge about adsorption characteristics limits the acquisition of phospholipase D (PLD) selec-tivity information for various phospholipids. In this study, we found that the adsorption equilibrium coefficient (KAds) of Streptomyces klenkii PLD (SkPLD) adsorption onto phosphatidylcholine (PC) monolayer films were inversely proportional to the acyl chain length of PC. SkPLD showed the greatest KAds value of 2.7 x 106 L mol-1 to 12:0/12:0-PC monolayer film, which was associated with the highest adsorption rate constant (ka) value (6.9 x 103 L mol-1 s-1). The high KAds value helped to enhance the specific activity (81.86 U/mg) of SkPLD toward 12:0/12:0-PC. Molecular dynamics simulation revealed that SkPLD was more dynamic in 12:0/12:0-PC, whereas more rigid in other membrane protein systems. When the conformation is too rigid, the enzyme activity will be reduced. Compared with other membrane protein systems, the suitable number of 18 hydrogen bonds between SkPLD and 12:0/12:0-PC monolayer film might contribute to an increase in KAds value, which would modulate the binding affinity of PLD molecules to the lipid-water interface, and it subsequently affected the catalytic activity. This study provided important information on the role of interfacial adsorption prosperities in con -trolling substrate recognition and enzyme activity of Streptomyces PLDs.