Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. Gel-state disorder in the presence of methyl iso- and anteiso-branched-chain substituents

Abstract

The hydrocarbon chain orientational order parameters of membranes of Acholeplasma laidlawii B enriched with large quantities of a linear saturated, a methyl iso-branched, or a methyl anteiso-branched fatty acid plus small quantities of various isomeric monofluoropalmitic acid probes were determined via fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR) over a range of temperatures spanning the gel to liquid-crystalline phase transitions (determined by differential scanning calorimetry). Membrane orientational order profiles in the liquid-crystalline state were generally similar regardless of the particular fatty acyl structure, showing a region of relatively constant order preceding a region of progressive decline in order toward the methyl terminus of the acyl chain. In the gel state, the order profile of the linear saturated fatty acid enriched membranes was characteristically flat, with little head to tail gradation of order. In contrast, the methyl iso-branched and the methyl anteiso-branched enriched membranes exhibited a local disordering in the gel phase reflected in a very pronounced head to tail gradient of order, which remained at temperatures below the lipid phase transition. In addition, the methyl iso- and anteiso-branched fatty acid enriched membranes were overall more disordered than the membrane containing only linear saturated fatty acyl groups. Thus, at a constant value of reduced temperature below the lipid phase transition, overall order decreased in the progression 15:0 greater than 16:0i greater than 16:0ai, suggesting that these methyl-branched substituents lower the lipid phase transition by disrupting the gel phase lipid chain packing.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. A direct comparison of the effects of cis- and trans-cyclopropane ring and double-bond substituents on orientational order

“…Since the presence of a cyclopropane ring or a double bond on an acyl chain adjacent to the MPFA had little if any effect on the orientational ordering of the MFPA, it must be concluded that in the liquid-crystalline state the two fatty acyl chains experience a degree of independence sufficient to negate any influence of structural substitutents in one acyl chain upon the orientational order of the other. Previous 19F NMR results have demonstrated that the orientational order profiles of the MFPA chains in membranes of A. laidlawii B are highly similar in the liquid-crystalline state whether those membranes were enriched with straight-chain saturated fatty acids such as 15:0 (Macdonald et al, 1983(Macdonald et al, , 1985c 280, 290, 300, 310, and 320 K), or (D) 19:0 , 9 (240*, 250*, 260*, 270*, 280*, 280, 290, 300, and 310 K). The numbers in parentheses represent the temperatures at which the order profiles, from top to bottom, were acquired.…”

A comparison of thermal adaptation of membrane lipids in psychrophilic and thermophilic bacteria

“…All these changes modulate membrane fluidity so as to keep an adequate proportion of liquid-crystalline lipid in the membrane. Furthermore, pure diisomethyIpalmitoyl-phosphatidylethanolamine gives a stable lamellar phase up to 98°C, whereas dipalmitoyl-phosphatidylethanolamin¢ forms a hexagonal-ll phase above 43.5°C [42], yet the fluidity of the branched-chain phosphatidylethanolamine is less than that of the unsaturated phosphatidylcthanolamine [31]. Branched-chain fatty acids form less well-ordered gel phases and do not give rise to phase separations of proteins at temperatures below the 177 liquid-crystalline-to-gel phase transition temperature [42][43][44][45].…”

A comparison of thermal adaptation of membrane lipids in psychrophilic and thermophilic bacteria

“…Another important aspect is the maintenance of the bilayer phase. Branched-chain fatty acids form less well-ordered gel phases and do not give rise to phase separations of proteins at temperatures below the 177 liquid-crystalline-to-gel phase transition temperature [42][43][44][45]. This has functional consequences in.…”

“…for instance, the thermal characteristics of sugar transport across the membrane [45]. Furthermore, pure diisomethyIpalmitoyl-phosphatidylethanolamine gives a stable lamellar phase up to 98°C, whereas dipalmitoyl-phosphatidylethanolamin¢ forms a hexagonal-ll phase above 43.5°C [42], yet the fluidity of the branched-chain phosphatidylethanolamine is less than that of the unsaturated phosphatidylcthanolamine [31]. Thus, it may be that the main reason why thermophiles commonly contain branched-chain fatty acids is to retain a functional bilayer tllat is not too fluid at high temperatures; thermophiles with rather low optin,~um growth temperatures, and also many me,:ephiles, also may have high contents of branched-chain fatty acids which are appropriate at lower temperatures because they give enough fluidity even in the gel phase to prevent the formation of separate liquid-crystalline domains into which proteins would aggregate.…”