Sphingolipid-cholesterol rafts diffuse as small entities in the plasma membrane of mammalian cells

To probe the dynamics and size of lipid rafts in the membrane of living cells, the local diffusion of single membrane proteins was measured. A laser trap was used to confine the motion of a bead bound to a raft protein to a small area (diam < or = 100 nm) and to measure its local diffusion by high resolution single particle tracking. Using protein constructs with identical ectodomains and different membrane regions and vice versa, we demonstrate that this method provides the viscous damping of the membrane domain in the lipid bilayer. When glycosylphosphatidylinositol (GPI) -anchored and transmembrane proteins are raft-associated, their diffusion becomes independent of the type of membrane anchor and is significantly reduced compared with that of nonraft transmembrane proteins. Cholesterol depletion accelerates the diffusion of raft-associated proteins for transmembrane raft proteins to the level of transmembrane nonraft proteins and for GPI-anchored proteins even further. Raft-associated GPI-anchored proteins were never observed to dissociate from the raft within the measurement intervals of up to 10 min. The measurements agree with lipid rafts being cholesterol-stabilized complexes of 26 +/- 13 nm in size diffusing as one entity for minutes.     

近金线属的分类地位及金线属的鉴别特征(鲤形目:鲤科:亚科)

本文根据系统学原理,提出了建立新类元的依据;并据此从分类和系统发育上论证了近金线属ＡｎｃｈｉｃｙｃｌｏｃｈｅｉｌｕｓＬｉｅｔＬａｎ独立成属的可能性,认为应将近金线属归于金线属;修订了金线属ＳｉｎｏｃｙｃｌｏｃｈｅｉｌｕｓＦａｎｇ的鉴别特征。     

大花黄牡丹分类学地位的研究

通过野外调查、引种试验,对大花黄牡丹与黄牡丹的形态特征、生长和繁殖特性进行了综合比较研究,结果表明,二者之间在植株高度、心皮数目、花色、花瓣基部有无棕红斑及繁殖特性等存在明显差异;同时,染色体组型、带型及蛋白亚基构成分析也表明二者之间有明显差异,因此我们认为,大花黄牡丹应上升为种的等级：Ｐａｅｏｎｉａ ｌｕｄｌｏｗｉｉ（Ｓｔｅｒｎ ｅｔ Ｔａｙｌｏｒ）Ｊ．Ｊ．Ｌｉ ｅｔ Ｄ．Ｚ．Ｃｈｅｎ,ｓｔａｔ     

Sex and the selfish herd: sexual segregation within nonmating whirligig groups

The fitness costs and benefits at different positions in fishshoals, bird flocks, and insect swarms can be asymmetric; agroup's edge may provide more feeding opportunities, but alsogreater predator risk. Animals make trade-offs between theseselection pressures based on individual differences in traitsincluding satiation level, ability to avoid predators, and sex.Previous studies did not evaluate the impact of sex on grouppositioning in these types of nonhierarchical, nonmating groupscalled congregations. A controlled laboratory experiment wasconducted, using marked whirligig beetles (Coleoptera: Gyrinidae),to test for sexual segregation and why different sexes mightchoose different positions. Soon after a disturbance, malesoften were found at the periphery and females at the centerof groups. There was also an overlying influence of feedingon position; satiated individuals moved toward the center andhungry individuals toward the periphery. Several minutes aftera disturbance, sexual segregation disappeared, but segregationdue to hunger persisted. Sexual segregation in this study wasbest explained by the predator avoidance hypothesis, not theenergy needs hypothesis. Females weighed less than males; thismay make them more at risk to predation because of reduced swimmingspeed or less mechanical protection from their exoskeleton.No difference between the sexes was found in the volume of theirdefensive chemicals. This is one of the first studies to showthat sex influences position of individuals within simple nonmatinggroups (congregations) and suggests that more attention shouldbe given to positional sex differences within shoals, flocks,herds, and swarms.     

Consequences of relative cellular positioning on quorum sensing and bacterial cell-to-cell communication

Cell-to-cell bacterial communication via diffusible signals is addressed and the conceptual framework in which quorum sensing is usually described is evaluated. By applying equations ruling the physical diffusion of the autoinducer molecules, one can calculate the gradient profiles that would occur either around a single cell or at the center of volumes of increasing size and increasing cell densities. Water-based matrices at 25 °C and viscous biofilms at colder temperatures are compared. Some basic consequences relevant for the field of microbial signalling arise. As regards induction, gradient-mixing dynamics between as little as two cells lying at a short distance appears to be sufficient for the buildup of a concentration reaching the known thresholds for quorum sensing. A straight line in which the highest concentrations occur is also created as a consequence of the gradient overlap geometry, providing an additional signal information potentially useful for chemotactic responses. In terms of whole population signalling, it is shown how the concentration perceived by a cell in the center is critically dependent not only on the cell density but also on the size of the biofilm itself. Tables and formulas for the practical prediction of N -acyl homoserine lactones concentrations at desired distances in different cell density biofilms are provided.     

Efficient identification of near‐native conformations in ab initio protein structure prediction using structural profiles

One of the major bottlenecks in many ab initio protein structure prediction methods is currently the selection of a small number of candidate structures for high‐resolution refinement from large sets of low‐resolution decoys. This step often includes a scoring by low‐resolution energy functions and a clustering of conformations by their pairwise root mean square deviations (RMSDs). As an efficient selection is crucial to reduce the overall computational cost of the predictions, any improvement in this direction can increase the overall performance of the predictions and the range of protein structures that can be predicted. We show here that the use of structural profiles, which can be predicted with good accuracy from the amino acid sequences of proteins, provides an efficient means to identify good candidate structures. Proteins 2010. © 2009 Wiley‐Liss, Inc.     

Amino acid 95 causes strong alteration of peptide position PΩ in HLA-B*41 variants

There have been several attempts over the years to identify positions in the peptide-binding region (PBR) of human leukocyte antigens (HLA) that influence the specificity of bound amino acids (AAs) at each position in the peptide. Originally, six pockets (A-F) were defined by calculating the surface area of the PBR on the crystal structure of HLA-A2 molecules. More recent crystallographic analyses of a variety of HLA alleles have led to broader pocket definitions. In this study, we examined the peptide-binding specificity of HLA-B*41 alleles and compared our results with the available pocket definitions. By generating recombinant HLA-B molecules and studying the eluted peptides by mass spectrometry and pool sequencing, we detected two different POmega peptide motifs within the B*41 group: Leu vs Val/Pro. Specificity was dependent on the presence of Leu (B*4102, B*4103, and B*4104) vs Trp (B*4101, B*4105, and B*4106) at AA position 95 in the HLA molecule, whose impact on POmega has been a subject of controversy in current pocket definitions. In contrast, the Arg97Ser mutation did not affect pocket F binding specificity in B*41 subtypes although residue 97 was previously identified as a modulator of peptide binding for several HLA class I alleles. According to most pocket definitions, this study shows that the Asn80Lys substitution in B*4105 impels the peptide's POmega anchor toward more promiscuity. Our sequencing results of peptides eluted from HLA-B*41 variants demonstrate the limitations of current pocket definitions and underline the need for an extended peptide motif database for improved understanding of peptide-major histocompatibility complex interactions.