Asymmetrical topology of diether- and tetraether-type polar lipids in membranes of Methanobacterium thermoautotrophicum cells.

H Morii,Y Koga

doi:10.1016/s0021-9258(17)34086-3

Abstract

We investigated the distribution of diether polar lipids between the inner and outer leaflets of the membrane of Methanobacterium thermoautotrophicum comparing the orientation of tetraether polar lipids, which constitute a monolayer in the same membrane. Three kinds of reactions were employed for intact cells or protoplasts and unsealed membrane fragments prepared from the organism: glycosidase digestion for glycolipids, NaIO4 oxidation for glycolipids and inositol lipids, and trinitrophenylation for aminophospholipids. The results indicated that (a) most gentiobiose residues of both diether and tetraether polar lipids were exposed on the outside of the cells; (b) serine and inositol residues of both diether and tetraether polar lipids were mainly oriented to the cytoplasmic surface of the membrane; and (c) approximately 80% of archaetidylethanolamine (diether type) was distributed in the outer leaflet of the membrane bilayer, while only 25% of the ethanolamine residue of gentiobiosyl caldarchaetidylethanolamine (tetraether type) was oriented to the outer surface of the membrane. These results, except for ethanolamine lipids, are consistent with the hypothesis that the tetraether polar lipids are synthesized from the corresponding diether polar lipid precursors that have been already substituted by polar groups in the membrane by head-to-head condensation without rearrangement of lipids.

Highlights

We investigated the distributionof diether polar lip- rangementinthemembrane [2]
According kinds of reactions were employed for intcaecltls or pro- to this hypothesis, the orientationof polar head groups of the toplasts and unsealed membrane fragments prepared tetraether polar lipids in the cytoplasmic membrane should from the organism: glycosidasdeigestionfor glycolipids, NaIO, oxidation for glycolipids andinositol lipids, and trinitrophenylationforaminophospholipids
The results indicatedthat ( a ) mostgentiobiose residues of both diether and tetraether polar lipids were exposed on the outside of the cells; ( b ) serine and inositol residues of both diether and tetraether polar lipids were coincide with the distributionof the corresponding diether polar lipids between the inner and outer leaflets of the membrane

Summary

MembrAasnyemmetry of Diether and Tetraether Lipids o lo o lo

NaIO, oxidation of the inositol groupin gentiobiosyl caldarchaetidylinositol in the intact cells was significantly slowerthan theoxidation of the lipid in the unsealed membrane fragments up to the 4-hpoint. This time course of chaetidylethanolamine), the reaction was similar to that of archaetidylinositol in both cases (Fig. 6, A and B ). In order to test the change inmem- membrane fragments were treated (Fig. 6D) These observabrane permeability after glycosidasedigestion of the mem- tions show that the glucose residues are mainlylocated on the brane glycolipids, penetration of TNBS into the protoplasts wasouter surface of intact cells. NaZO, Oxidation-Phosphatidylinositol-specific phospho- darchaetidylinositol would be principally exposed to the outer lipase C is capableof cleaving to the inositol lipid of methano- surface of the membrane, and the inositol residue of the lipid gens [16]; it could not be applied to the orientation would be oriented toward the intracellular space

Membrane Asymmetry of Diether and Tetraether Lipids

Findings

DISCUSSION