Glycolipid membrane surface structure: orientation, conformation, and motion of a disaccharide headgroup

Abstract

The orientation of the disaccharide headgroup of a lactose-containing lipid, 3-O-(4-O-beta-D-galactopyranosyl-beta-D-glucopyranosyl)-1,2-di-O-tetrade cyl-sn- glycerol (DTLL), relative to the surface of bilayer membranes has been determined via 2H NMR. The lactosyl headgroup is extended away from the membrane surface into the aqueous phase. The headgroup motion has axial symmetry as evidenced by the spectral line shape and order parameter tensor. 2H NMR of oriented multibilayers of DTLL confirms that the director of motional averaging is the bilayer normal. The two sugar residues have segmental order parameters S (glucose, 0.53; galactose, 0.51) which indicate that the headgroup fluctuates about the bilayer normal as a rigid unit. 2H spin-lattice relaxation times T1z for deuterons on each of the two sugar rings are similar, indicating further that there is no substantial motion about the disaccharide linkage within the headgroup. The magnitude of the relaxation times (4 ms) suggests that the rigid body motions of the headgroup are approaching the Larmor frequency; however, they increase with increasing temperature, indicating that the motions are rapid enough to be in the fast motional regime (omega o2 tau c2 less than 1). The conformation about the galactose-glucose intersaccharide linkage, calculated from the 2H NMR data, is shown to differ substantially from those found in X-ray diffraction studies of crystalline lactose and high-resolution NMR studies of methyl lactoside in nonviscous solution. The orientations of the hydroxymethyl groups in the headgroup have been calculated from the 2H NMR data. For the galactosyl residue the data are consistent with the presence of more than one rotamer about the C5"-C6" bond which are in fast exchange on the 2H NMR time scale. The hydroxymethyl group of the glucose residue exists in two rotameric forms about the C5'-C6' bond which have relative populations of ca. 2:1 and which are in slow exchange on the 2H NMR time scale (10(-5) s). The two rotamers differ from those deduced from X-ray crystallography of crystalline lactose and 13C NMR studies of methyl lactoside in solution.

Studies on the molecular recognition of synthetic methyl β‐lactoside analogs by ricin, a cytotoxic plant lectin

“…For compound 1 there are six local minima under a level of relative steric energy of 16.72 kJ/mol, and four of them (A, B, C and C') are included in a region with A E < 4 kJ/mol which describes approximately 5% of the complete energy surface in terms of q and w. The energy barriers are 8.8 kJ/mol between A and B, 9.6 kJ/mol between A and C, and 7.1 kJ/mol between B and C. Depending on the orientation of the hydroxymethyl group at the glucose residue [47] there are two different sets of torsion angles for conformer C (conformations C and C'). The interglycosidic torsion angles for these conformers compared to those previously determined for some p(1 + 4)-linked disaccharides by X-ray diffraction methods are also given in and E (cp/y, 175"/-2") have not been reported, although the structure of the disaccharide headgroup of a lactose containing glycolipid may be oriented as conformers C and C' on the membrane surface [54] and conformer E describes the geometry of some synthetic interglycosidic acetal derivatives of lactose and cellobiose [55].…”

“…5. As previously discussed this conformational behaviour is in accordance with the solid state structure of Plactose [48], which is very close to conformer A, with the conformation in solution for 3C-enriched methyl fl-lactoside (l), also determined as conformer A on the basis of I3C-NMR data [%I; and with that of the disaccharide head group of 3-0-P-lactosyl-I ,2-O-tetradecyl-sn-glycerol which moves on the membrane surface in a conformation very close to C or C', according to 2H-NMR [54]. Conformer A would be favored by the exo-anomeric effect [62].…”

Ceramide glycanase from the earthworm, Lumbricus terrestris

“…The following compounds were generously given: n-butyl-,l-lactoside, n-octyl-/-lactoside, myristoyl-,/-lactoside, stearoyl-,3-lactoside and phytyl-,f-lactoside from Dr. R. T. C. Huang, Institut fur Molekularbiologie und Biochemie, Freie Universitat, Berlin 33, Germany; lactosyldialkylglycerol [14] from Dr. H. Jarrell, National Research Council of Canada, Ottawa, Ontario, Canada; nLcOse4Cer and LcOse3Cer, from Dr. S. Basu, University of Notre Dame, Notre Dame, IN, U.S.A. The following materials were purchased from commercial sources: GM3I GMl, GT1b, GlcCer, GalCer and sphingomyelin from Supelco (Bellefonte, PA, U.S.A.); GDla from Biocarb Chemicals, Lund, Sweden; OTE-,f-lactoside, CETE-fl-lactoside and Triton X-100, from Pierce Chemical Co.; octyl-Sepharose from Pharmacia; p-nitrophenylglycosides, 4-methylumbelliferyl-NeuAc, methyl-,/-lactoside, ethyl-fl-lactoside, n-propyl-fl-lactoside, benzyl-fi-lactoside, ceramide type III (mainly non-hydroxy fatty acids), sodium cholate, sodium deoxycholate, octyl-,J-glucoside and PAP-SGal-agarose, from Sigma; sodium taurodeoxycholate, sodium taurodehydrocholate, sodium taurolithocholate, sodium taurocholate and sodium taurochenodeoxycholate, from Calbiochem; Rotofor cell isoelectrofocusing unit and Bio-Gel A-0.5m, from Bio-Rad; Silica-gel-60-precoated plates from Merck, Darmstadt, Germany.…”

“…The isoelectric point of earthworm CGase was determined by isoelectrofocusing using a Rotofor cell isoelectrofocusing unit [23]. The purity of earthworm CGase preparations was examined by PAGE using [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] % gradient gels under non-denaturing conditions with Coomassie Blue stain [15]. Purification …”

Structures of Lipid Assemblies

“…What is likely is that these headgroups probably describe, in some cases, relatively fixed structures, and in other more complicated headgroups, flexible structures. 58,59 Some of the experiments that led to the observations and conclusions just described cannot be performed on biological membranes for technical reasons. Therefore limited measures of phospholipid conformation are available for biological membranes.…”