Erythrocyte membrane proteins and membrane skeleton

Considerable advances in the research field of erythrocyte membrane were achieved in the recent two decades. New findings in the structure-function correlation and interactions of erythrocyte membrane proteins have attracted extensive attention. Interesting progress was also made in the molecular pathogenesis of erythrocyte membrane disorders. Advances in the composition, function and interaction of erythrocyte membrane proteins, erythrocyte membrane skeleton, and relevant diseases are briefly described and summarized here on the basis of domestic and world literatures. Translated from Life Science Research, 2005, 9(4): 283–291 [译自: 生命科学研究]     

Erythrocyte membrane proteins and membrane skeleton

Considerable advances in the research field of erythrocyte membrane were achieved in the recent two decades.New findings in the structure-function correlation and interactions of erythrocyte membrane proteins have attracted extensive attention.Interesting progress was also made in the molecular pathogenesis of erythrocyte membrane disorders.Advances in the composition,function and interaction of erythrocyte membrane proteins,erythrocyte membrane skeleton,and relevant diseases are briefly described and summarized here on the basis of domestic and world literatures.     

植物叶绿体类囊体膜及膜蛋白研究进展

叶绿体是植物和真核藻类进行光合作用的场所。存在于叶绿体类囊体膜上的蛋白质复合物含有光反应所需的光合色素和电子传递链组分,在光合作用过程中,光化学反应发生在类囊体膜上。因此,类囊体膜是光能向化学能转化的主要场所,因而也一直是光合作用研究的热点。叶绿体类囊体膜的深入研究可以促进光合作用的分子机理研究。该文就叶绿体类囊体膜的三维构象及类囊体膜蛋白的组成和功能研究进行了综述。     

Paleontological evidence for membrane fusion between a unit membrane and a half-unit membrane

Membrane fusion is of fundamental importance for many biological processes and has been a topic of intensive research in past decades with several models being proposed for it. Fossils had previously not been considered relevant to studies on membrane fusion. But here two different membrane fusion patterns are reported in the same well-preserved fossil plant from the Miocene (15-20 million years old) at Clarkia, Idaho, US. Scanning electron microscope, transmission electron microscope, and traditional studies reveal the vesicles in various states (even transient semi-fusion) of membrane fusion, and thus shed new light on their membrane structure and fusion during exocytoses. The new evidence suggests that vesicles in plant cells may have not only a unit membrane but also a half-unit membrane, and that a previously overlooked membrane fusion pattern exists in plant cells. This unexpected result from an unexpected material not only marks the first evidence of on-going physiological activities in fossil plants, but also raises questions on membrane fusion in recent plants.     

Palaeontological evidence for membrane fusion between a unit membrane and a half-unit membrane

Membrane fusion is of fundamental importance for many biological processes and has been a topic of intensive research in past decades with several models being proposed for it. Fossils had previously not been considered relevant to studies on membrane fusion. But here two different membrane fusion patterns are reported in the same well-preserved fossil plant from the Miocene (15–20 million years old) at Clarkia, Idaho, US. Scanning electron microscope, transmission electron microscope, and traditional studies reveal the vesicles in various states (even transient semi-fusion) of membrane fusion, and thus shed new light on their membrane structure and fusion during exocytoses. The new evidence suggests that vesicles in plant cells may have not only a unit membrane but also a half-unit membrane, and that a previously overlooked membrane fusion pattern exists in plant cells. This unexpected result from an unexpected material not only marks the first evidence of on-going physiological activities in fossil plants, but also raises questions on membrane fusion in recent plants.     

Origin of magnetosome membrane: proteomic analysis of magnetosome membrane and comparison with cytoplasmic membrane

Prokaryotes are known to have evolved one or more unique organelles. Although several hypotheses have been proposed concerning the biogenesis of these intracellular components, the majority of these proposals remains unclear. Magnetotactic bacteria synthesize intracellular magnetosomes that are enclosed by lipid bilayer membranes. From the identification and characterization of several surface and transmembrane magnetosome proteins, we have postulated that magnetosomes are derived from the cytoplasmic membrane (CM). To confirm this hypothesis, a comparative proteomic analysis of the magnetosome membrane (MM) and CM of the magnetotactic bacterium, Magnetospirillum magneticum AMB-1, was undertaken. Based on the whole genome sequence of M. magneticum AMB-1, 78 identified MM proteins were also found to be prevalent in the CM, several of which are related to magnetosome biosynthesis, such as Mms13, which is tightly bound on the magnetite surface. Fatty acid analysis was also conducted, and showed a striking similarity between the CM and MM profiles. These results suggest that the MM is derived from the CM.     

Nucleoside diphosphatase: membrane asymmetry, membrane binding and latency of a peripheral membrane protein

Nucleoside diphosphatase is a peripheral protein of the endoplasmic reticulum in the liver. This review brings together the available information on the properties of the membrane-associated form of the enzyme found in microsomal vesicles. The data are consistent with the view that the enzyme is loosely bound to the inner surface of the vesicles and, therefore, to the luminal surface of the endoplasmic reticulum in vivo.     

Detergent-resistant membrane subfractions containing proteins of plasma membrane, mitochondrial, and internal membrane origins

HEK293 cell detergent-resistant membranes (DRMs) isolated by the standard homogenization protocol employing a Teflon pestle homogenizer yielded a prominent opaque band at approximately 16% sucrose upon density gradient ultracentrifugation. In contrast, cell disruption using a ground glass tissue homogenizer generated three distinct DRM populations migrating at approximately 10%, 14%, and 20% sucrose, named DRM subfractions A, B, and C, respectively. Separation of the DRM subfractions by mechanical disruption suggested that they are physically associated within the cellular environment, but can be dissociated by shear forces generated during vigorous homogenization. All three DRM subfractions possessed cholesterol and ganglioside G_M1, but differed in protein composition. Subfraction A was enriched in flotillin-1 and contained little caveolin-1. In contrast, subfractions B and C were enriched in caveolin-1. Subfraction C contained several mitochondrial membrane proteins, including mitofilin and porins. Only subfraction B appeared to contain significant amounts of plasma membrane-associated proteins, as revealed by cell surface labeling studies. A similar distribution of DRM subfractions, as assessed by separation of flotillin-1 and caveolin-1 immunoreactivities, was observed in CHO cells, in 3T3-L1 adipocytes, and in HEK293 cells lysed in detergent-free carbonate. Teflon pestle homogenization of HEK293 cells in the presence of the actin-disrupting agent latrunculin B generated DRM subfractions A–C. The microtubule-disrupting agent vinblastine did not facilitate DRM subfraction separation, and DRMs prepared from fibroblasts of vimentin-null mice were present as a single major band on sucrose gradients, unless pre-treated with latrunculin B. These results suggest that the DRM subfractions are interconnected by the actin cytoskeleton, and not by microtubes or vimentin intermediate filaments. The subfractions described may prove useful in studying discrete protein populations associated with detergent-resistant membranes, and their potential interactions in cell signaling.     

Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on membrane fouling

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated to minimize the effect of suspended solids on membrane fouling. The MBMBR and a conventional membrane bioreactor (CMBR) were operated in parallel for about two months. Unexpectedly, the rate of membrane fouling in MBMBR was about three times of that in CMBR. MBMBR showed a higher cake layer resistance than CMBR due to plenty of filamentous bacteria inhabited in suspended solids in MBMBR. Protein and polysaccharide contents of soluble EPS in MBMBR were obviously larger than those in CMBR. It could be speculated that the overgrowth of filamentous bacteria in MBMBR resulted in severe cake layer and induced a large quantity of EPS, which deteriorated the membrane fouling.     

Modulation of membrane dynamics and cell motility by membrane tension

The plasma membrane of most cells is drawn tightly over the cytoskeleton of the cell, resulting in a significant tension being developed in the membrane. The tension in the membrane can be calculated from the force required to separate it from the cytoskeleton; and the force itself can be measured rapidly by using laser tweezers. Recent observations indicate that decreasing membrane tension stimulates endocytosis and increasing tension stimulates secretion. Thus, membrane tension provides a simple physical mechanism to control the area of the plasma membrane. Here, we speculate that tension is a global parameter that the cell uses to control physically plasma membrane dynamics, cell shape and cell motility.     

The plasma membrane and mitochondrial membrane potentials of Plasmodium yoelii

1. The plasma membrane potential and the mitochondrial membrane potential of P. yoellii was examined by fluorescence microscopy using rhodamine 123 and by transmembrane distribution of tetraphenylphosphonium. 2. The mitochondrion of P. yoelii, free of gametocyte stage, maintained a high negative inside membrane potential. 3. Deprivation of glucose in incubation medium largely abolished the plasma membrane potential but not the mitochondrial membrane potential. 4. Studies with metabolic inhibitors showed that the mitochondrial membrane potential constituted a marginal portion as compared with the plasma membrane potential in intact infected erythrocytes.     

Glycopeptides from bovine liver basement membrane and plasma membrane.

Proteolytic digests of liver plasma-cell membranes from the cow were fractionated to yield two homogeneous glycopeptides and a third preparation about 92% pure. The composition of the two homogeneous glycopeptides made it clear that they were derived from basement membrane material rather than the plasma membrane. Ruminants are unusual in having large amounts of basement membrane in the liver while other animals generally have little or none. Both basement-membrane-derived glycopeptides contained a glucosyl galactosyl disaccharide linked to hydroxylysine, the smaller one contained no other sugar structure but the larger one contained in addition an acidic heterosaccharide, the two chains probably being linked separately to the same molecule. Smith degradation and beta-elimination operations show that this heterosaccharide has an inner structure containing mannose and hexosamine, with the sugars galactose, N-glycollyl-neuraminic acid and fucose situated more peripherally. The amino-acid-heterosaccharide linkage is alkali stable. The third glycopeptide, which may be plasma-membrane-derived, differs from the heterosaccharide described above in that it contains no glucose and contains some O-seryl and O-threonyl amino-acid--sugar linkage. It, too, has a periodate-resistant structure of hexosamine and mannose.     

Erythrocyte membrane cholesterol levels and their effects on membrane proteins

The susceptibility of the band 3 protein of the erythrocyte membrane to proteolytic digestion at either surface of the membrane was not altered when the membrane cholesterol level was increased by 65–103%. Cross-linking of the major membrane proteins by o-phenanthroline · Cu, glutaraldehyde, dimethylsuberimidate and dimethyladipimidate was also unaffected.