Sphingomyelin analogs with branched N-acyl chains: the position of branching dramatically affects acyl chain order and sterol interactions in bilayer membranes.
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 degrees 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.
Jaikishan
Shishir
S
Biochemistry, Department of biosciences, Åbo Akademi University, 20520 Turku, Finland.
Björkbom
Anders
A
Slotte
J Peter
JP
D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D013109:Sphingomyelins / Q000737:chemistry*; D013261:Sterols / Q000737:chemistry*; D013696:Temperature
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; D013109:Sphingomyelins; D013261:Sterols; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine