Mammalian Prion protein expression in yeast; a model for transmembrane insertion

The prion protein (PrP), a GPI-anchored glycoprotein, is inefficiently secreted by mammalian microsomes, 50% being found as transmembrane (TM) proteins with the central TM1 segment spanning the membrane. TM1 hydrophobicity is marginal for lateral membrane insertion, which is primarily driven by hydrophobic interaction between the ER translocon and substrates in transit. Most inserted TM1 has its N-terminus in the ER lumen (Ntm orientation), as expected for arrest of normal secretion. However, 20% is found in inverted Ctm orientation. These are minor species in vivo, presumably a consequence of efficient quality control. PrP mutations that increase TM1 hydrophobicity result in increased Ctm insertion, both in vitro and in mouse brain, and a strong correlation is found between CtmPrP insertion and neuropathology in transgenic mice; a copper-dependent pathogenicity mechanism is suggested. PrP fusions with a C-terminal epitope tag, when expressed in yeast cells at moderate levels, appear to interact efficiently with the translocon, providing a useful model for testing the effects of PrP mutations on TM insertion and orientation. However, secretion of PrP by the mammalian translocon requires the TRAP complex, absent in yeast, where essentially all PrP ends up as TM species, 85–90% Ntm and 10–15% Ctm. Although yeast is, therefore, an incomplete mimic of mammalian PrP trafficking, effects on Ctm insertion of mutations increasing TM1 hydrophobicity closely reflect those seen in vitro. Electrostatic substrate-translocon interactions are a major determinant of TM protein insertion orientation and the yeast model was used to investigate the role of the large negative charge difference across TM1, a likely cause of translocation delay that would favor TM insertion and Ctm orientation. An increase in ΔCh from −5 to −7 caused a marked increase in Ctm insertion, while a decrease to −3 or −1 allowed 35 and about 65% secretion, respectively. Utility of the yeast model and the role of this charge difference in driving PrP membrane insertion are confirmed.     

重金属 Ni2+ 对亚洲玉米螟生长发育和生殖行为的影响

【目的】探索农田重金属Ni²⁺污染对植食性昆虫潜在的影响。【方法】在人工饲料中添加不同浓度（1, 5, 10, 15和20 mg/kg）的重金属Ni²⁺,以不添加重金属的人工饲料为对照,实验室条件下饲养亚洲玉米螟 Ostrinia furnacalis (Guenée)初孵幼虫,系统观察其各项生长发育和生殖行为指标参数。【结果】Ni ²⁺对亚洲玉米螟幼虫期、蛹期、化蛹率和羽化率有抑制作用;对亚洲玉米螟雌蛹重有促进作用,但随Ni²⁺浓度的升高而逐渐减弱;低浓度Ni²⁺（1~10 mg/kg）对雄蛹重有促进作用,高浓度Ni²⁺（15~20 mg/kg）对雄蛹重有抑制作用。随着Ni²⁺浓度的增加,亚洲玉米螟雌蛾平均求偶持续时间逐渐减小;1 mg/kg Ni²⁺浓度下雌蛾求偶率及求偶高峰期出现的时间与对照组基本一致,其余4个Ni²⁺浓度都对雌蛾求偶行为产生影响且表现为求偶高峰期出现的时间提前,最高求偶率均小于100%。5 mg/kg Ni²⁺对亚洲玉米螟雄蛾定向行为有促进作用,其余浓度则表现为抑制作用。Ni²⁺对亚洲玉米螟雌蛾的产卵量和卵孵化率均产生了显著的抑制作用。【结论】重金属Ni²⁺对亚洲玉米螟的生长发育和生殖行为产生了影响。     

Separation of Spatio-Temporal Receptive Fields into Sums of Gaussian Components

Visual cortical simple cells have been experimentally shown to reveal non-trivial spatio-temporal orientation tuning functions comprising different phases of specifically tuned enhanced and suppressed activity. A recently developed analytical method based on nonlinear neural field models suggests that such space-time responses should be approximately separable into a sum of temporally amplitude modulated Gaussian spatial components. In the present work, we investigate this possibility by means of numerical fits of sums of Gaussians to response functions observed in experiments and computer simulations. Because the theory relates each single component to a particular connectivity kernel between the underlying cell classes shaping the response, the relative contribution of feedforward and cortex-intrinsical excitatory and inhibitory feedback mechanisms to single cell tuning can be approached and quantified in experimental data.     

The orientation of the sandhopper <Emphasis Type="Italic">Talitrus saltator</Emphasis> during a partial solar eclipse

To acquire more information about the identification and use of the sun and other celestial cues in the sea–land orientation of the sandhopper Talitrus saltator, we carried out releases in a confined environment during a partial solar eclipse and at sunset. The sandhoppers were unable to identify the sun (86% covered) during the eclipse nor to use other celestial compass factors of orientation. This was probably due to the low level of light intensity (close to the minimum level for orientation recorded at sunset) and to the variations in intensity and pattern of skylight polarization.     

Adaptive Growth of Gymnosperm Branches-Ultrastructural and Micromechanical Examinations

The top, the lateral and the underside of basal branch segments of two gymnosperm species, spruce (Picea abies [L.] Karst.) and yew (Taxus baccata L.), were studied with respect to possible adaptation in structural and mechanical properties. Microtensile tests were performed on thin wet foils, which were removed from the periphery of the branches. Structural parameters such as density and the microfibril angle in the S2-layer were examined to investigate the structure-function relationships of the branch wood. The top, the lateral and the underside of both branches showed significant differences in their structural and mechanical properties. However, no significant variations were observed as a function of age and size development. The findings were discussed in view of adaptive growth strategies of trees, including biomechanical constraints of a horizontally growing branch.     

Conformational preferences of the amylin nucleation site in SDS micelles: an NMR study

Human islet amyloid polypeptide (hIAPP), or amylin, is a 37 amino acid hormone secreted by pancreatic beta-cells. hIAPP constitutes approximately 90% of the amyloid deposits found in type II diabetic patients. It has been shown that the central region of the peptide (hIAPP(20-29)) constitutes the nucleation site for the amyloidogenic process with F23 playing a key role in the formation of the beta-pleated structures. In addition, it has been proposed that an important stage in the cytotoxicity of hIAPP is its interaction with the beta-cell membranes. As a first step toward the characterization of the interaction of hIAPP with cell membranes, we determined conformational preferences of hIAPP(20-29) in membrane-mimicking environments. We found that upon interacting with negatively charged micelles, the dominant conformation of hIAPP(20-29) is a distorted type I beta-turn centered on residues F23 and G24, with F23, A25, and I26 forming a small hydrophobic cluster that may facilitate the interaction of this peptide with the membrane bilayer. Moreover, we were able to elucidate the topological orientation of the peptide that is absorbed on the micelle surface, with the hydrophobic cluster oriented toward the hydrocarbon region of the micelles and both N- and C-termini exposed to the solvent.     

Molecular dynamics simulation studies of cytochrome b5 from outer mitochondrial and microsomal membrane

Two forms of cytochrome b(5) have been identified, associated with the outer membrane of liver mitochondria (OM cyt b(5)) and with the membrane of the endoplasmic reticulum (microsomal, Mc cyt b(5)). These proteins have very similar structures, but differ significantly in physical properties, with the OM cyt b(5) exhibiting a more negative reduction potential, higher stability, and stronger interactions with the heme. We perform molecular dynamics simulations to probe the structures and fluctuations of the two proteins in solution, to help explain the observed physical differences. We find that the structures of the two proteins, highly similar in the crystal, differ in position of a surface loop involving residues 49-51 in solution. Hydrophobic residues Ala-18, Ile-32, Leu-36, and Leu-47 tend to cluster together on the surface of rat OM cyt b(5), blocking water access to the protein interior. In bovine Mc cyt b(5), two of these positions, Ser-18 and Arg-47, are occupied by hydrophilic residues. This leads to breaking the hydrophobic cluster and allowing the protein to occupy a more open conformation. A measure of this structural transition is the opening of a cleft on the protein surface, which is 5 A wider in the OM cyt b(5) simulation compared to the Mc form. The OM protein also appears to have a more compact hydrophobic core in its beta-sheet region. These effects may be used to explain observed stability differences between the two proteins.     

Relative lengths of fingers and toes in human males and females

Digital scans of the hands and feet were obtained from 62 heterosexual females and 60 heterosexual males. Scans only of the hands were obtained from 29 homosexual females and 35 homosexual males. The lengths of the individual fingers and toes were estimated from those images by two experienced judges, and length ratios were constructed for all possible pairs of fingers (or toes) on each hand (or foot). Thumbs were not measured, but the great toe was measured and used to construct length ratios. Past research had concentrated on the relative lengths of the index and ring fingers (the 2D:4D ratio). This ratio is close to 1.0 in females and smaller than 1.0 in males. Here 2D:4D did exhibit the largest sex difference, for both hands, followed by 2D:5D and 3D:4D. The sex differences were larger for the right hand than for the left. For both homosexual females and homosexual males, nearly all of the length ratios for fingers were intermediate to those for heterosexual females and heterosexual males; that is, the ratios of homosexual females were masculinized and those of homosexual males were hypomasculinized, but few of these differences were significant. Because many toes were substantially arched, acceptable estimates of length often could not be obtained from the two-dimensional scans, meaning that conclusions about toes are much less certain than those for fingers. Nevertheless, the length ratios were generally larger for toes than for fingers, and the sex differences were generally smaller for toes.     

Towards high-resolution solid-state NMR on large uniformly 15N- and [13C,15N]-labeled membrane proteins in oriented lipid bilayers

Based on exact numerical simulations, taking into account isotropic and conformation-dependent anisotropic nuclear spin interactions, we systematically analyse the prospects for high-resolution solid-state NMR on large isotope-labeled membrane proteins macroscopically oriented in phospholipid bilayers. Using the known X-ray structures of rhodopsin and porin as models for large membrane proteins with typical -helical and -barrel structural motifs, the analysis considers all possible one- to six-dimensional spectra comprised of frequency dimensions with evolution under any combination of amide ¹H, amide ¹⁵N, and carbonyl ¹³C chemical shifts as well as ¹H-¹⁵N dipole-dipole couplings. Under consideration of typical nuclear spin interaction and experimental line-shape parameters, the analysis provides new insight into the resolution capability and orientation-dependent transfer efficiency of existing experiments as well as guidelines as to improved experimental approaches for the study of large uniformly ¹⁵N- and [¹³C,¹⁵N]-labeled membrane proteins. On basis of these results and numerical optimizations of coherence-transfer efficiencies, we propose several new high-resolution experiments for sequential protein backbone assignment and structure determination.     

A new group-selection model for the evolution of homosexuality

Abstract. Scientists have long puzzled over how homosexual orientation has evolved, given the assumed low relative fitness of homosexual individuals compared to heterosexual individuals. A number of theoretical models for the evolution of homosexuality have been postulated including balance polymorphism, "Fertile females", hypervariability of DNA sequences, kin selection, and "parental manipulation". In this paper, I propose a new group-selection model for the evolution of homosexuality which offers two advantages over existing models: (1) its non-assumption of genetic determinism, and (2) its lack of dependency on an inefficient altruism relation and family dynamics theory.