Groups with Polar Characteristics Can Locate at Both Shallow and Deep Locations in Membranes:  The Behavior of Dansyl and Related Probes

Abstract

To understand the relationship between the chemical structure of polar molecules and their membrane location, the behavior of dansyl (dimethylaminonaphthalenesulfonyl) and related polar fluorescent probes was examined. The depth of these probes in lipid bilayers was determined by parallax analysis of fluorescence quenching [Chattopadhyay and London (1987) Biochemistry 26, 39-45; Abrams & London, Biochemistry (1993) 32, 10826-10831]. Quenching was measured for dansyl groups: (1) attached to the polar headgroup of PE, (2) linked to an alkyl chain, (3) attached to the end of a fatty acyl chain, and (4) attached to the polar headgroup of PE via a spacer group. In all cases, the dansyl probes located in the polar headgroup region, 19-21 A from the bilayer center. This shows the dansyl group has a strong tendency to seek a shallow location in the polar headgroup region. The only exception to this pattern was in the case of a dialkylated dansyl, for which two populations were observed. One population was at the polar headgroup level, but the second was deeply buried in the acyl chain region. To see if the polar sulfonamide group of dansyl influences depth, a structurally related probe substituting a thiocarbamoyl linkage, dimethylaminonaphthalenethiocarbamoyl (dantyl)-labeled PE, was synthesized. Dantyl groups were located deeper than dansyl groups, 13-16 A from the bilayer center. There was an even more dramatic difference in depth between dansyl and mansyl (methylanilinonaphthalenesulfonyl) derivatives. Mansyl probes, which have an extra phenyl group relative to dansyl, were found to locate deeply within the acyl chain region of the bilayer (6-7 A from the bilayer center) when attached to the polar headgroup of PE. Thus, the membrane location of polar groups depends strongly on the details of their chemical structure, and it is possible for a polar group to locate both at shallow and deep locations. These results suggest the energy to bury a polar moiety in the hydrophobic part of the bilayer is not prohibitively high. This contrasts to the behavior of charged groups, which appear to be restricted to shallow locations in membranes. In this report, the effect of populations at two different depths on the parallax analysis is also considered.

Different Membrane Anchoring Positions of Tryptophan and Lysine in Synthetic Transmembrane α-Helical Peptides

“…We propose that the tryptophan side chain has a specific affinity for a well defined site near the interface, with the indole imino moiety positioned near the center of the lipid carbonyl region, and the fused aromatic rings in contact with the lipid acyl chains. This location is in good agreement with the membrane depth of NH-containing carbazole indole analogs, as determined by parallax analysis of fluorescence quenching (32,42) but is on average somewhat deeper in the membrane than NMR studies on other small Trp analogs predict (43). In both studies, however, these watersoluble analogs are not part of a transmembraneous peptide.…”

Electron paramagnetic resonance (EPR) spectral components of spin-labeled lipids in saturated phospholipid bilayers: effect of cholesterol

“…The results of the present work are in agreement with studies by fluorescence spectroscopy, which have also shown that several membrane probes may occupy both shallow and deep locations in the bilayer. [3][4][5][6][7] A study with the fluorescent probe 4'-dimethylamino-3-hydroxyflavone in bilayer vesicles of EYPC has shown that the addition of 30 mol % cholesterol induced strong changes in the concentrations of the probe in H-bonded and H-bond free forms, suggesting redistribution of the dye from the membrane surface to the hydrophobic region of the bilayer. 5 Moreover, similar relocations of the probe Prodan caused by cholesterol were also observed in model membranes of phosphatidylcholines.…”

“…Studies of bilayer systems using fluorescence spectroscopy have also shown that several membrane probes may occupy at least two locations in the bilayer characterized by distinct polarity and hydration. [3][4][5][6][7] The origin of this bimodal distribution has been interpreted based on the ability of these probes to participate in intermolecular hydrogen bonding within the membrane -a polar site at the bilayer interface where the probe is H-bonded to water and an apolar site with no H-bonding to water. 5 Interestingly, hydrostatic pressure applied on multilamellar vesicles of DMPC causes the relocation of the fluorescent probe Prodan towards more hydrophobic environments in the membrane.…”

Effects of cholesterol in chylomicron remnant models of lipid emulsions on apoE-mediated uptake and cytotoxicity of macrophages

“…The mean fluorescence lifetime of dansyl-PE was used to evaluate PC head group hydration at the lipid particle surface. Dansyl fluorophores are located at the PC head group region in membranes (36,37), and the lifetime of the excited state reflects their local polarity, to which water is the major contributing factor (38). The mean fluorescence lifetime in TO-PC/Chol emulsions is shorter than that in TO-PC emulsions, indicative of an increase in head group hydration at the TO-PC/Chol emulsion surface.…”