Relations between Structure and Function in Cytoplasmic Membrane Vesicles Isolated from an Escherichia coli Fatty‐Acid Auxotroph

Abstract

The results presented in this paper establish relationships between structural, morphological and functional properties of cytoplasmic membrane vesicles isolated from an Escherichia coli unsaturated fatty acid auxotroph. The membranes were isolated from cells grown in the presence of either oleic, linoleic, linolenic or elaidic acids.High-angle X-ray diffraction studies show that the order-disorder transitions induced by temperature variations and associated with the paraffin chains of the lipids are a function of the fatty acid composition of the membranes. In some cases "cocrystallization" of various lipid species takes place within a single type of ordered domains. In other cases there is segregation of various lipid species into more than one distinct type of ordered domain.The various order-disorder transitions observed induce morphological changes in the hydrophobic core of the membranes which can be detected by freeze-etch electron microscopy. A random distribution of particles on the fracture faces is observed when the paraffin chains of the lipids are disordered. Upon ordering of the paraffin chains, particles are excluded from the ordered domains and as a consequence, smooth areas and areas with densely packed particles are observed. The ratio of the smooth surface to particulated surface is proportional to the amount of ordered paraffin chains present. Moreover, the size of the smooth domains is a function of the fatty acid composition of the membranes.Discontinuities in the rate of D-lactate-dependent proline uptake as a function of temperature correlate with the order-disorder transitions observed. The high energies of activation at low temperatures are attributed to decreased mobility of the carrier proteins upon aggregation. In contrast, phosphoenolpyruvate-dependent vectorial phosphorylation does not respond to the ordering of the paraffin chains.The aim of the present work is to establish correlations between structural, morphological and physiological properties of membranes. Such studies have been undertaken previously and a variety of techniques have been used to determine the conformation of the paraffin chains of Escherichia coli membrane lipids, e.g. fluorescence [l, 21, electron spin resonance [3 -61 and high-angle X-ray diffraction [7,8]. The most direct technique is high-angle X-ray diffraction since it provides a quantitative evaluation of the fraction of the paraffin chains in the ordered and disordered conformation. Moreover, this technique allows an assessment of the segregation of different lipid species. Because of technical limitations however, high-angle X-ray diffraction has been used generally in a qualitative manner in the study of biological membranes. As a consequence, it has not yet been possible to determine the various lipid segregations taking place during the order-disorder transitions of the paraffin chains and to establish the correlations that exist between these segregations and the physiological properties of the membranes.Eur. J. Biochem. 49 (1974)

Lipid and protein segregation in Escherichia coli membrane: morphological and structural study of different cytoplasmic membrane fractions.

“…The techniques used in this study have been described previously (3,8,10). Further details are given in the text and figure legends.…”

“…We have demonstrated previously (3) that cytoplasmic membrane vesicles of Escherichia coli containing specific unsaturated fatty acids exhibit relatively large areas (i.e., several thousand A in diameter) of smooth and particulated surfaces when frozen from temperatures below the order-disorder transition of the hydrocarbon chains. Since the two domains are radically different, discrete fractions of cytoplasmic membrane vesicles can be isolated that exhibit different relative amounts of smooth and heavily particulated surfaces (8,9).…”

“…When frozen from temperatures below the transition, membrane fracture faces usually display a mixture of smooth surfaces devoid of particles and surfaces containing aggregrated particles. In certain special cases, lipid segregation can also be visualized by freeze-fracture electron microscopy (2,3).…”

“…Segregation of lipids and proteins in biological membranes can be induced by conformational transitions of the hydrocarbon chains of the membrane lipids from a disordered to an ordered state (1)(2)(3)(4). Lipidsegregation is the consequence of membrane lipid heterogeneity, which may lead to a lateral lipid phase separation during the disorder-to-order transition (5,6).…”

Physico‐Chemical Properties of Phosphatidylglycerol in Membranes of Acholeplasma laidlawii

“…Lipid phase transitions in membranes have been demonstrated by X-ray diffraction [12,13], spin label mobility [14], differential scanning calorimetry [15], changes in fluorescence intensity of a membrane probe [16] and by changes in activation energy of membranebound lipid-dependent enzymes [13,17,18]. In general these are essentially averaging techniques, showing the phase transition of the total lipid in the membrane.…”