Structure and phase behavior of a charged glycolipid (1,2-O-dialkyl-3-O-.beta.-D-glucuronosyl-sn-glycerol)

Abstract

In order to investigate the effects of a net surface charge on the properties of glycolipid membranes, we have synthesized a glyceroglycolipid, 1,2-O-dialkyl-3-O-beta-D-glucuronosyl- sn-glycerol (GlcUA lipid), with saturated alkyl chains of varying length (14, 16, and 18 carbon atoms; 14-, 16-, and 18-GlcUA, respectively) and glucuronic acid with an ionizable 6-carboxyl group as polar residue. Aqueous dispersions of GlcUA lipids have been characterized by differential scanning calorimetry, densitometry, and X-ray diffraction methods as a function of pH. The carboxyl group deprotonation of apparent pK about 5.5 leads to a decrease of the melting temperatures by about 7 degrees C for all three compounds and to a chain-length-dependent reduction of the transition enthalpies by 0, 7, and 14% for 14-, 16-, and 18-GlcUA, respectively. The decrease of the transition temperature is consistent with current electrostatic concepts and models of charged membrane interfaces, but the chain-length-specific dependence of the enthalpy decrease with an increase of pH shows that the pH effects in GlcUA lipids are not of purely electrostatic origin. However, these effects appear to be simpler in some instances than corresponding effects in phospholipids with multiply ionizable head groups. For this reason, the lipids with the glucuronic acid head group appear to represent an appropriate model system for studies of net electric charge effects on the membrane properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Columnar DNA Superlattices in Lamellar o-Ethylphosphatidylcholine Lipoplexes: Mechanism of the Gel-Liquid Crystalline Lipid Phase Transition

“…If this change is supposed to be due solely to the change of the lipid surface charge density during the transition, the expected change in the lipid specific volume during the transition would be Δυ ∼0.1 mL/g (a value of 1.03 mL/g for the lipid specific volume in the liquid crystalline phase as measured for DSPC 22 was used for this estimation). Such a value for the specific volume change is within the limits of those typically reported for the melting transition of lipids, although close to the upper limit. , A similar value of Δυ = 0.098 mL/g was measured, for example, with another charged lipid of 18 carbon atom chains − dioctadecyl-β- d -glucuronosyl- sn -glycerol . A possible source for a large volume change of the cationic EDSPC upon the phase transition is also the interdigitated nature of its gel phase.…”

A Bifunctional Glycosyltransferase from Agrobacterium tumefaciens Synthesizes Monoglucosyl and Glucuronosyl Diacylglycerol under Phosphate Deprivation

“…In this case, the regulative enzyme is a processive glycosyltransferase adjusting the ratio of MGlcD and DGlcD (22). A novel and alternative regulation mechanism would be the introduction of different headgroups into the glycolipid by a bifunctional glycosyltransferase as shown for Agt (this study), with GlcAD probably as a bilayer-forming glycolipid (46). Therefore, Agt may be an interesting candidate for a new type of glycosyltransferase playing a role for the membrane bilayer formation and function under phosphate deprivation.…”

Studies of the Structure and Organization of Cationic Lipid Bilayer Membranes: Calorimetric, Spectroscopic, and X-Ray Diffraction Studies of Linear Saturated P-O-Ethyl Phosphatidylcholines

“…These observations suggest the formation of uncorrelated lipid lamellae, the result of excessive swelling of the interlamellar spaces owing to charge repulsion between the positively charged lipid surfaces. However, comparable behavior was not observed with the longer-chain homologs, although continuous and excessive swelling of the interlamellar spaces often occurs when charged lamellar-forming amphiphiles are dispersed in low ionic-strength aqueous media (see Hauser, 1984;Koynova et al, 1993). The possibility of a chain length-dependent component to this type of behavior is also consistent with the results of recent x-ray diffraction studies, which demonstrate that whereas aqueous dispersions of the cationic amphiphile di-O-myristoyl-3-N,N,N-trimethylaminopropane forms uncorrelated lamellae in the fluid phase , the longer chain di-O-oleoyl derivative forms large multilamellar structures under comparable conditions (Koltover et al, 1999).…”