Biochimica et Biophysica Acta (BBA) - Reviews on Biomembranes最新文献

Gangliosides exist as a very complex mixture of species differing in both the hydrophilic and hydrophobic moieties. They are particularly abundant in the central nervous system (CNS), where they have been associated with development and maturation of the brain, neuritogenesis, synaptic transmission, memory formation and synaptic aging. Today, many data suggest that some of the effects exerted by gangliosides are due to interactions with proteins that participate in the transduction of signals through the membrane in membrane microdomains. A specific characteristic of CNS gangliosides is the structure of their long-chain base (LCB). In fact, considering all the mammalian cell sphingolipids, gangliosides, sulphatides, neutral glycosphingolipids, sphingomyelin and ceramides, it would seem that while the LCB with 18 carbons is the main component of all sphingolipids, only CNS gangliosides contain significant amounts of LCB with 20 carbons. C18-Sphingosine is always present in cell gangliosides; the individual ganglioside species containing C18-sphingosine increase during cell differentiation then remain constant during cell aging. Gangliosides containing C20-sphingosine are absent, or present only in traces, in undifferentiated cells but with the onset of cell differentiation they appear, their content slowly but continuously increasing throughout the life span. In this review we discuss the chemistry, physico-chemistry and metabolism of ganglioside species differing in LCB length and introduce the hypothesis that the varying ratio between C18- and C20-gangliosides during CNS development and aging can be instrumental in modulating membrane domain organisation and cell properties.

The plasma membrane H⁺-ATPase from fungi and plants is a proton pump which plays a key role in the physiology of these organisms controlling essential functions such as nutrient uptake and intracellular pH regulation. In fungal and plant cells the activity of the proton pump is regulated by a large number of environmental factors at both transcriptional and post-translational levels. During the last years the powerful tools of molecular biology have been successfully used in fungi and plants allowing the cloning of a wide diversity of H⁺-ATPase genes and rapid progress on the molecular basis of reaction mechanism and regulation of the proton pump. This review focuses on recent results on regulation of plasma membrane H⁺-ATPase obtained by molecular approaches.

The last two decades have witnessed a break-through in identifying and understanding the functions of both the proteins and lipids of bacterial membranes. This development was parallelled by increasing insights into the biogenesis, topology, transport and sorting of membrane proteins. However, progress in research on the membrane distribution and transport of lipids in bacteria has been slow in that period. The development of novel biochemical in vitro approaches and recent genetic studies have increased our understanding of these subjects. The aim of this review is to present an overview of the current knowledge of the distribution and transport of lipids in both Gram-positive and Gram-negative bacteria. Special attention is paid to recently obtained results, which are expected to inspire further research to finally unravel these poorly understood phenomena.

The G-protein coupled receptors form a large and diverse multi-gene superfamily with many important physiological functions. As such, they have become important targets in pharmaceutical research. Molecular modelling and site-directed mutagenesis have played an important role in our increasing understanding of the structural basis of drug action at these receptors. Aspects of this understanding, how these techniques can be used within a drug-design programme, and remaining challenges for the future are reviewed.

In this review, we summarize the results of recent studies on the main phase transition behavior of phospholipid bilayers using the combined approaches of molecular mechanics simulations and high-resolution differential scanning calorimetry. Following a brief overview of the phase transition phenomenon exhibited by the lipid bilayer, we begin with the review by showing how several structural parameters underlying various phospholipids including phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol are defined and determined. Specifically, these structural parameters are obtained with saturated lipids packed in the gel-state bilayer using computer-based molecular mechanics calculations. Then we proceed to present the calorimetric data obtained with the lipid bilayer composed of saturated phospholipids as it undergoes the gel-to-liquid-crystalline phase transition in excess water. The general equations that can correlate the gel-to-liquid-crystalline phase transition temperature (T_m) of the lipid bilayer with the structural parameters of the lipid molecule constituting the lipid bilayer are subsequently presented. From these equations, two tables of predicated T_m values for well over 400 molecular species of saturated phosphatidylcholine and saturated phosphatidylethanolamine are generated. We further review the structure and chain-melting behavior of a large number of sn-1 saturated/sn-2 unsaturated phospholipids. Two T_m-diagrams are shown, from which the effects of the number and the position of one to five cis carbon–carbon double bonds on T_m can be viewed simultaneously. Finally, in the last part of this review, simple molecular models that have been invoked to interpret the characteristic T_m trends exhibited by lipid bilayers composed of unsaturated lipids with different numbers and positions of cis carbon–carbon double bonds as seen in the T_m-diagram are presented.

Mitochondrial biogenesis utilizes a complex proteinaceous machinery for the import of cytosolically synthesized preproteins. At least three large multisubunit protein complexes, one in the outer membrane and two in the inner membrane, have been identified. These translocase complexes cooperate with soluble proteins from the cytosol, the intermembrane space and the matrix. The translocation of presequence-containing preproteins through the outer membrane channel includes successive electrostatic interactions of the charged mitochondrial targeting sequence with a chain of import components. Translocation across the inner mitochondrial membrane utilizes the energy of the proton motive force of the inner membrane and the hydrolysis of ATP. The matrix chaperone system of the mitochondrial heat shock protein 70 forms an ATP-dependent import motor by interaction with the polypeptide chain in transit and components of the inner membrane translocase. The precursors of integral inner membrane proteins of the metabolite carrier family interact with newly identified import components of the intermembrane space and are inserted into the inner membrane by a second translocase complex. A comparison of the full set of import components between the yeast Sacccharomyces cerevisiae and the nematode Caenorhabditis elegans demonstrates an evolutionary conservation of most components of the mitochondrial import machinery with a possible greater divergence for the import pathway of the inner membrane carrier proteins.