Neuronal microtubules: when the MAP is the roadblock

Recent studies shed new light on a potential cascade of events by which neurological diseases such as Alzheimer's lead to axonal degeneration. In this model, the pathology starts with an elevation in microtubule-associated proteins (MAPs) such as tau. This renders the microtubules less accessible to motor proteins, which impairs their capacity to sustain anterograde axonal transport of proteins and organelles. In response, the neuron hyperphosphorylates tau so that it dissociates from the microtubules. Unfortunately, the hyperphosphorylated tau forms abnormal filaments that are deleterious to the axon, and the tau-depleted microtubules become highly sensitive to microtubule-severing proteins such as katanin.     

ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion--Part II: shoulder, elbow, wrist and hand

In this communication, the Standardization and Terminology Committee (STC) of the International Society of Biomechanics proposes a definition of a joint coordinate system (JCS) for the shoulder, elbow, wrist, and hand. For each joint, a standard for the local axis system in each articulating segment or bone is generated. These axes then standardize the JCS. The STC is publishing these recommendations so as to encourage their use, to stimulate feedback and discussion, and to facilitate further revisions. Adopting these standards will lead to better communication among researchers and clinicians.     

Human factor H-related protein 5 has cofactor activity, inhibits C3 convertase activity, binds heparin and C-reactive protein, and associates with lipoprotein

Factor H-related protein 5 (FHR-5) is a recently discovered member of the factor H (fH)-related protein family. FHR proteins are structurally similar to the complement regulator fH, but their biological functions remain poorly defined. FHR-5 is synthesized in the liver and consists of 9 short consensus repeats (SCRs), which display various degrees of homology to those of fH and the other FHR proteins. FHR-5 colocalizes with complement deposits in vivo and binds C3b in vitro, suggesting a role in complement regulation or localization. The current study examined whether rFHR-5 exhibits properties similar to those of fH, including heparin binding, CRP binding, cofactor activity for the factor I-mediated degradation of C3b and decay acceleration of the C3 convertase. rFHR-5 bound heparin-BSA and heparin-agarose and a defined series of truncations expressed in Pichia pastoris localized the heparin-binding region to within SCRs 5-7. rFHR-5 bound CRP, and this binding was also localized to SCRs 5-7. FHR-5 inhibited alternative pathway C3 convertase activity in a fluid phase assay; however, dissociation of the convertase was not observed in a solid phase assay. rFHR-5 displayed factor I-dependent cofactor activity for C3b cleavage, although it was apparently less effective than fH. In addition, we demonstrate association of FHR-5 with high density lipid lipoprotein complexes in human plasma. These results demonstrate that FHR-5 shares properties of heparin and CRP binding and lipoprotein association with one or more of the other FHRs but is unique among this family of proteins in possessing independent complement-regulatory activity.     

Diversity of methanotrophic bacteria in tropical upland soils under different land uses

Three upland soils from Thailand, a natural forest, a 16-year-old reforested site, and an agricultural field, were studied with regard to methane uptake and the community composition of methanotrophic bacteria (MB). The methane uptake rates were similar to rates described previously for forest and farmland soils of the temperate zone. The rates were lower at the agricultural site than at the native forest and reforested sites. The sites also differed in the MB community composition, which was characterized by denaturing gradient gel electrophoresis (DGGE) of pmoA gene fragments (coding for a subunit of particulate methane monooxygenase) that were PCR amplified from total soil DNA extracts. Cluster analysis based on the DGGE banding patterns indicated that the MB communities at the forested and reforested sites were similar to each other but different from that at the farmland site. Sequence analysis of excised DGGE bands indicated that Methylobacter spp. and Methylocystis spp. were present. Sequences of the "forest soil cluster" or "upland soil cluster alpha," which is postulated to represent organisms involved in atmospheric methane consumption in diverse soils, were detected only in samples from the native forest and reforested sites. Additional sequences that may represent uncultivated groups of MB in the Gammaproteobacteria were also detected.     

A critical reassessment of penetratin translocation across lipid membranes

Penetratin is a short, basic cell-penetrating peptide able to induce cellular uptake of a vast variety of large, hydrophilic cargos. We have reassessed the highly controversial issue of direct permeation of the strongly cationic peptide across negatively charged lipid membranes. Confocal laser scanning microscopy on rhodamine-labeled giant vesicles incubated with carboxyfluorescein-labeled penetratin yielded no evidence of transbilayer movement, in contradiction to previously reported results. Confocal fluorescence spectroscopy on black lipid membranes confirmed this finding, which was also not affected by application of a transmembrane electric potential difference. A novel dialysis assay based on tryptophan absorbance and fluorescence spectroscopy demonstrated that the permeability of small and large unilamellar vesicles to penetratin is <10(-13) m/s. Taken together, the results show that penetratin is not capable of overcoming model membrane systems irrespective of the bilayer curvature or the presence of a transmembrane voltage. Thus, direct translocation across the hydrophobic core of the plasma membrane cannot account for the efficient uptake of penetratin into live cells, which is in accord with recent in vitro studies underlining the importance of endocytosis in the internalization process of cationic cell-penetrating peptides.     

Attenuation of insulin-stimulated insulin receptor substrate-1 serine 307 phosphorylation in insulin resistance of type 2 diabetes

Insulin resistance is a primary characteristic of type 2 diabetes and likely causally related to the pathogenesis of the disease. It is a result of defects in signal transduction from the cell surface receptor of insulin to target effects. We found that insulin-stimulated phosphorylation of serine 307 (corresponding to serine 302 in the murine sequence) in the immediate downstream mediator protein of the insulin receptor, insulin receptor substrate-1 (IRS1), is required for efficient insulin signaling and that this phosphorylation is attenuated in adipocytes from patients with type 2 diabetes. Inhibition of serine 307 phosphorylation by rapamycin mimicked type 2 diabetes and reduced the sensitivity of IRS1 tyrosine phosphorylation in response to insulin, while stimulation of the phosphorylation by okadaic acid, in cells from patients with type 2 diabetes, rescued cells from insulin resistance. EC(50) for insulin-stimulated phosphorylation of serine 307 was about 0.2 nM with a t(1/2) of about 2 min. The amount of IRS1 was similar in cells from non-diabetic and diabetic subjects. These findings identify a molecular mechanism for insulin resistance in non-selected patients with type 2 diabetes.     

Ca2+-surfactant interactions affect enzyme stability in detergent solutions

Detergent proteases and amylases generally bind Ca(2+) ions. These bound ions enhance enzyme stability, reducing the rates of degradative reactions such as unfolding and proteolysis. Thus, surfactant aggregates, such as micelles, affect protease and amylase stability indirectly, by competing with the enzymes for Ca(2+) ions. Dissociation constants for Ca(2+) interactions with anionic surfactant micelles are in the 10(-3) to 10(-2) M range. These interactions are weak relative to enzyme-Ca(2+) interactions (K(d) of order 10(-6) M). However, surfactant is typically present at much higher concentration than enzyme, and it is the Ca(2+)-micelle equilibrium that largely determines the amount of free Ca(2+) available for binding to enzymes. The problem of surfactant-mediated Ca(2+) removal from enzymes can be avoided by adding calcium to a detergent formulation in an amount such that the concentration of free Ca(2+) is around 10(-5)M.     

In Candida albicans hyphae,Sec2p is physically associated with SEC2 mRNA on secretory vesicles

Candida albicans hyphae grow in a highly polarized fashion from their tips. This polarized growth requires the continuous delivery of secretory vesicles to the tip region. Vesicle delivery depends on Sec2p, the Guanine Exchange Factor (GEF) for the Rab GTPase Sec4p. GTP bound Sec4p is required for the transit of secretory vesicles from the trans‐Golgi to sites of polarized growth. We previously showed that phosphorylation of Sec2p at residue S584 was necessary for Sec2p to support hyphal, but not yeast growth. Here we show that on secretory vesicles SEC2 mRNA is physically associated with Sec2p. Moreover, we show that the phosphorylation of S584 allows SEC2 mRNA to dissociate from Sec2p and we speculate that this is necessary for Sec2p function and/or translation. During hyphal extension, the growing tip may be separated from the nucleus by up to 15 μm. Transport of SEC2 mRNA on secretory vesicles to the tip localizes SEC2 translation to tip allowing a sufficient accumulation of this key protein at the site of polarized growth.     

Metabolic Syndrome and Changes in Body Fat From a Low‐fat Diet and/or Exercise Randomized Controlled Trial

It is difficult to identify the successful component(s) related to changes in metabolic syndrome (MetS) from lifestyle interventions: the weight loss, the behavior change, or the combination. The purpose of this study is to determine the effects of a weight‐stable randomized controlled trial of low‐fat diet and exercise, alone and in combination, on MetS. Men (n = 179) and postmenopausal women (n = 149) with elevated low‐density lipoprotein cholesterol (LDL‐C) and low high‐density lipoprotein cholesterol (HDL‐C) were randomized into a 1‐year, weight‐stable trial with four treatment groups: control (C), diet (D), exercise (E), or diet plus exercise (D+E). MetS was defined using a continuous score. Changes in MetS score (ΔMetS) were compared between groups using analysis of covariance, stratified by gender and using two models, with and without baseline and change in percent body fat (ΔBF) as a covariate. In men, ΔMetS was higher for D vs. C (P = 0.04), D+E vs. C (P = 0.0002), and D+E vs. E (P = 0.02). For women, ΔMetS was greater for D vs. C (P = 0.045), E vs. C (P = 0.02), and D+E vs. C (P = 0.004). After adjusting for ΔBF, all differences between groups were attenuated and no longer significant. ΔMetS were associated with ΔBF for both men (P < 0.0001) and women (P = 0.004). After adjustment for ΔBF, low‐fat diet alone and in combination with exercise had no effect on MetS. The key component for MetS from low‐fat diet and/or increased physical activity appears to be body fat loss.