Deuterium nuclear magnetic resonance investigation of the effects of proteins and polypeptides on hydrocarbon chain order in model membrane systems

Abstract

Deuterium Fourier-transform nuclear magnetic resonance spectra have been obtained of 1-myristoyl 2-(14,14,14-trideutero)myristoyl phosphatidylcholine bilayers at 34.1 MHz by using the quadrupole echo pulse technique. Thereby, we have investigated the effects upon the deuterated dimyristoyl phosphatidylcholine bilayers of the following proteins and polypeptides: gramicidin A, bacteriophage f1 coat protein, beef brain myelin proteolipid apoprotein, cytochrome b 5 , and cytochrome c oxidase (ferrocytochrome c :oxygen oxidoreductase, EC 1.9.3.1). Above T c , the transition temperature between the gel and liquid crystal phases, the quadrupole splitting of the deuterium-labeled methyl group is reduced or collapsed in the presence of protein or polypeptide. No evidence has been found for ordered “boundary lipid.” Below T c , the spectra show that the hydrocarbon chains are prevented from crystallizing by the protein (or polypeptide) incorporated in the membrane. Similar disordering effects above T c are also seen when an unsaturated lipid, 1-(16,16,16-trideutero)palmitoyl 2-palmitoleyl phosphatidylcholine is complexed with cytochrome oxidase.

The use of proton‐enhanced, natural abundance 13C NMR to study the molecular dynamics of model and biological membranes

“…In addition since TIP is also shorter in the mixed systems, the relative intensity of the low frequency motion undergone by the acyl chains has increased. This supports the observations in [2] and shows that on the NlvlR timescale employed here (-IO-' s) the effect of lipid-protein or lipidcholesterol interactions is the production of an increase in the low frequency dynamic disorder. Examination of the order resonant peaks shows that apart from minor relative changes in the TC_H and TIP of the headgroup and terminal methyl peaks, the reduction is a general property of the mixed systems.…”

“…Recent deuterium NMR studies of a series of lipid-protein dispersions have shown, however, that the quadrupolar splittings, derived from lipids with deuterated methylene groups, are freq uently reduced compared to those obtained from the same labels in pure lipid bilayers [ 2,7]. These observations have been interpreted as indicating an increase in the amplitude of the low frequency (-10' Hz) motion undergone by the lipid acyl chains in the presence of the protein [2]. It is argued that the frequency of this additional lipid motion is insufficiently rapid to cause a reduction in the hyperfme field splittings seen in the ESR spectrum.…”

Lipid polymorphism and the functional roles of lipids in biological membranes

“…Further, evidence exists for rapid exchange between annular lipid and bulk lipid [21], an observation inconsistent with the presence of bound lipid vital to function. This latter observation is at variance with evidence presented for relatively immobilized boundary lipid in reconstituted cytochrome oxidase systems [22], but more recent work is fully consistent with rapid exchange between annular and bulk bilayer lipid [23,24]. Thus, while the possibility remains that the local fluidity or lipid composition may affect protein function, the evidence supporting such proposals as a general rationale for the variety of lipids in biomembranes must be regarded as inconclusive.…”

Theory of protein-lipid and protein-protein interactions in bilayer membranes.

“…DISCUSSION Connection to Experiments. There is currently a great deal of discussion about whether membrane proteins order or immobilize nearby lipids (1,3,4,13,14). The present theory models either situation, depending on the value chosen for uo.…”

“…7 we estimated that T = 0 lies <20 degrees below the transition temperature. The experiments (13) on which this estimate was based have been criticized (14). The …”