Sphingomyelin analogs with branched N-acyl chains: The position of branching dramatically affects acyl chain order and sterol interactions in bilayer membranes

• Published in: Biochimica et biophysica acta 2010-10, Vol.1798 (10), p.1987-1994
• Main Authors: Jaikishan, Shishir, Björkbom, Anders, Slotte, J. Peter
• Format: Article
• Language: English
• Subjects: Calorimetry; Calorimetry, Differential Scanning; Cholesterol - chemistry; Cholesterol interaction; DPH anisotropy; Fluorescence quenching; Lipid Bilayers - chemistry; Lipid interaction; Membrane domain; Phosphatidylcholines - chemistry; Phospholipids - chemistry; Sphingomyelins - chemistry; Sterols - chemistry; Temperature
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2010.07.006

Sphingolipids have been found to have single methyl branchings both in their long-chain base and in their N-linked acyl chains. In this study we determined how methyl-branching in the N-linked acyl chain of sphingomyelin (SM) affected their membrane properties. SM analogs with a single methyl-branching at carbon 15 (of a 17:0 acyl chain; anteiso) had a lower gel–liquid transition temperature as compared to an iso-branched SM analog. Phytanoyl SM (methyls at carbons 3, 7, 11 and 15) as well as a SM analog with a methyl on carbon 10 in a hexadecanoyl chain failed to show a gel–liquid transition above 10 °C. Only the two distally branched SM analogs (iso and anteiso) formed ordered domains with cholesterol in a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer. However, domains formed by the branched SM analogs appeared to contain less sterol when compared to palmitoyl SM (PSM) as the saturated phospholipid. Sterol-enriched domains formed by the anteiso SM analog were also less stable against temperature than domains formed by PSM. Both the 10-methyl and phytanoyl SM analogs failed to form sterol-enriched domains in the POPC bilayer. Acyl chain branching weakened SM/sterol interactions markedly when compared to PSM, as also evidenced from the decreased affinity of cholestatrienol to bilayers containing branched SM analogs. Our results show that methyl-branching weakened intermolecular interactions in a position-dependent manner. ►Single methyl-branching in the N-acyl chain of SM disorders bilayer packing. ►The disordering effect is position-dependent (midchain position most disordered). ►Methyl-branching attenuate SM-cholesterol interaction. ►Methyl-branching could be a mean to confer disorder without cis double-bonds (chemically more inert).