A role for phospholipid polyunsaturation in modulating membrane protein function

Lipids. 1996 Mar;31 Suppl:S193-7. doi: 10.1007/BF02637075.

Abstract

Visual transduction is one of the best characterized G protein--coupled signalling systems. In addition, about 50% of the disk membrane phospholipid acyl chains are 22:6n-3, making this system ideal for determining the role of polyunsaturation in modulating membrane-signalling systems. The extent of formation of metarhodopsin II (MII), the G protein--activating photointermediate of rhodopsin, was studied in phospholipid vesicles composed of a variety of phosphatidylcholines, differing in their acyl chain composition at the sn-2 position. The amount of MII formed increased progressively with the level of acyl chain unsaturation at the sn-2 position. The effect of added cholesterol was to reduce the amount of MII formed. The acyl chain packing free volume of the rhodopsin containing lipid vesicles was characterized by a fractional volume parameter fv derived from measurements of the time-resolved fluorescence anisotropy decay of the hydrophobic membrane probe 1,6-diphenyl-1,3,5-hexatriene. The relationship among sn-2 acyl chain unsaturation, cholesterol content, and MII formation is explained on the basis of variation in fv with bilayer lipid composition and a novel model for the packing of phospholipids containing polyenoic acyl chains, such as 22:6n-3.

MeSH terms

  • Fats, Unsaturated / chemistry*
  • Fluorescence Polarization
  • Membrane Proteins / physiology*
  • Phospholipids / chemistry*
  • Rhodopsin / analogs & derivatives*
  • Rhodopsin / biosynthesis

Substances

  • Fats, Unsaturated
  • Membrane Proteins
  • Phospholipids
  • metarhodopsins
  • Rhodopsin