Exchange rates and numbers of annular lipids for the calcium and magnesium ion dependent adenosine triphosphatase

Abstract

A spin-labeled phospholipid is used to study lipid-protein interactions in the (Ca2+,Mg2+)-ATPase of sarcoplasmic reticulum from muscle. A novel null method is used to decompose composite electron spin resonance spectra into two components, characteristic of immobilized and mobile environments. Calculations based on a random mixing model suggest that protein-protein interactions will be relatively rare in these systems and that the immobilized lipid does not represent lipid trapped between proteins but rather represents annular phospholipid at the lipid-protein interface of the adenosinetriphosphatase. The apparent decrease in the amount of immobilized lipid with increasing temperature is shown to be consistent with lipid exchange between bulk and annulus, characterized by an exchange time of 10(-7) s at 37 degrees C. A minimum number of annular phospholipid sites of 32 and 22 are calculated at 0 and 37 degrees C, respectively.

Interaction of lipids with the neurotensin receptor 1

“…The low N b value does not arise from random protein-protein contacts at the low lipid:protein molar ratios studied here because the probability of protein-protein contacts is still very low at these molar ratios [46] as evidenced for rhodopsin and numerous other membrane proteins studied this way [45]. Furthermore, random protein-protein contacts would decrease upon increasing lipid:protein molar ratio, and here this is not the case as N b remains constant from 40:1 to 80:1 lipid:protein molar ratios (Table 1).…”

“…The slow and fast motion components in the composite spectra were determined by spectral addition as described in refs. [45,46]. Single-component spectra libraries were obtained from 14-PCSL in C18:1PC membranes recorded from 2 to 35°C at 1°C intervals for the fast motion component, and from 14-PCSL in sonicated C14:0PC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) membranes recorded from 0 to 20°C at 3 or 4°C intervals for the slow motion component.…”

G protein coupled receptor interactions with cholesterol deep in the membrane

“…The relationship between a cholesterol molecule bound in the cleft and the surrounding annular (boundary) phospholipids is shown in Fig. 8A, where annular phospholipid molecules are here defined as those for which the central two (C2 or C3) of the four beads representing the saturated chains or the central three (C2, D3, or C4) of the five beads representing the unsaturated chains are within 6 Å of the protein surface, consistent with EPR studies of membranes using spinlabelled phospholipids where the best resolution between annular and bulk lipids was obtained with a spin label at a position close to the middle of the fatty acyl chain [37][38][39]. The simulations show a cholesterol molecule bound at cluster A1 to be effectively adsorbed into the protein surface and covered by the fatty acyl chains of the annular phospholipid molecules (Fig.…”

Oxidative injury induced by hypochlorous acid to Ca-ATPase from sarcoplasmic reticulum of skeletal muscle and protective effect of trolox

“…The transmembrane domain of Ca-ATPase of skeletal muscle SR makes contact with about 30 lipid molecules in the membrane (East et al 1985;Dalton et al 1998). The major lipids of the SR membrane are PCs, PEs and phosphatidylinositols (Krainev et al 1995;Dalton et al 1998).…”