Abstract
Sphingolipids such as ceramide are recognized as vital regulators of many biological processes. Neutral sphingomyelinase 2 (nSMase2) is one of the key enzymes regulating ceramide production. It was previously shown that the enzymatic activity of nSMase2 was dependent on anionic phospholipids (APLs). In this study, the structural requirements for APL-selective binding of nSMase2 were determined and characterized. Using lipid-protein overlay assays, nSMase2 interacted specifically and directly with several APLs, including phosphatidylserine and phosphatidic acid. Lipid-protein binding studies of deletion mutants identified two discrete APL binding domains in the N terminus of nSMase2. Further, mutagenesis experiments pinpointed the core sequences and major cationic amino acids in the domains that are necessary for the cooperative activation of nSMase2 by APLs. The first domain included the first amino-terminal hydrophobic segment and Arg-33, which were essential for nSMase2 to interact with APLs. The second binding domain was comprised of the second hydrophobic segment and Arg-92 and Arg-93. Moreover, mutation of one or both domains decreased APL binding and APL-dependent catalytic activity of nSMase2. Further, mutation of both domains in nSMase2 reduced its plasma membrane localization. Finally, these binding domains are also important for the capability of nSMase2 to rescue the defects of yeast lacking the nSMase homologue, ISC1. In conclusion, these data have identified the APL binding domains of nSMase2 for the first time. The analysis of interactions between nSMase2 and APLs will contribute to our understanding of signaling pathways mediated by sphingolipid metabolites.