Isolation and characterization of an ether-linked homoserine lipid from the thylakoid membrane of Chlamydomonas reinhardtii 137+.

A polar diacylglycerolipid isolated from the phototrophic green alga Chlamydomonas reinhardtii 137+ (wild-type) displays chromatographic and chemical identity with the either-linked homoserine lipid 1(3),2-diacylglyceryl-(3)-O-4'(N,N,N-trimethyl)homoserine (DGTS) of the golden alga Ochromonas danica. Subcellularly, DGTS is a constituent of a fraction of thylakoid membranes purified from Chlamydomonas whole-cell homogenates. The proportion of DGTS in the photosynthetic lamellae is approximately 40% of the total found in the alga. Cellular and thylakoid-membrane DGTS both have an unsaturated:saturated ratio of about 1.8 and contain predominantly hexadecanoic and octadecanoic fatty acids. Quantitatively, the fatty acid complement of thylakoid DGTS is distinct from the cellular DGTS fatty acid profile. The results provide the first demonstrations that DGTS is a bona fide membrane lipid and, specifically, that ether-linked homoserine lipid is a component of the thylakoid membrane of a phototrophic green-plant cell.