Effect of Amide-Linked Acyl Chain Length on the Sphingomyelin-Cholesterol Interactions

Abstract

Sphingolipids are important component of eukaryotic membrane and are crucial for several physical as well as biological processes in cells. Sphingolipids play key role in the lateral domain formations which further assists in cell signalling and various significant cellular phenomena. Even though sphingolipids display an extensive diversity in their structures both in the head group and hydrophobic region, sphingosine (D-erythro-2-amino-trans-4-octadecene-1, 3-diol) is the prevalent backbone in most mammalian sphingolipids, including sphingomyelin (SM). The aim of this study was to examine how variation in the chain length in SM affect their bilayer properties as well as their interactions with cholesterol. We have synthesized SM analogs with different amide- linked acyl chains (14:0, 15:0, 16:0, 17:0, 18:0, 19:0, 20:0, 22:0 and 24:0). The main transition temperature and the degree of acyl chain order in pure SM bilayers was determined from the steady-state anisotropy of diphenylhexatriene. Ordered domain formation and sterol interaction with SM analogs was determined from the quenching susceptibility of dihenylhexatriene and cholestatrienol. Sterol affinity to fluid bilayer membranes containing saturated SM analogs was determined using a cholestatrienol equilibrium partitioning assay. We found that all SM analogs formed ordered domains ina fluid bilayer. Sterol was always included in these ordered domains, albeit to a varying degree. The thermostability of the ordered domains was remarkably similar, even though the SM acyl chaing length varied (16-24 carbons). Only 14:0 and 15:0 SM formed less thermostable ordered domains. We hope our results will enable us to better understand the behavior of asymmetric SM molecules in complex membranes, and to predict how they influence properties of biological membranes.