Animal navigation: longitude at last

Newly hatched sea turtles exposed to artificially generated magnetic fields with parameters characteristic of two sites 3700 km apart, differing only in longitude, can distinguish the two apparent locations and orient appropriately.     

Epidermal coumaroyl anthocyanins protect sweet basil against excess light stress: multiple consequences of light attenuation

The putative photoprotective role of foliar anthocyanins continues to attract heated debate. Strikingly different experimental set‐ups coupled with a poor knowledge of anthocyanin identity have likely contributed to such disparate opinions. Here, the photosynthetic responses to 30 or 100% solar irradiance were compared in two cultivars of basil, the green‐leafed Tigullio (TG) and the purple‐leafed Red Rubin (RR). Coumaroyl anthocyanins in RR leaf epidermis significantly mitigated the effects of high light stress. In full sunlight, RR leaves displayed several shade‐plant traits; they transferred less energy than did TG to photosystem II (PSII), and non‐photochemical quenching was lower. The higher xanthophyll cycle activity in TG was insufficient to prevent inactivation of PSII in full sunlight. However, TG was the more efficient in the shade; RR was far less able to accommodate a large change in irradiance. Investment of carbon to phenylpropanoid biosynthesis was more in RR than in TG in the shade, and was either greatly enhanced in TG or varied little in RR because of high sunlight. The metabolic cost of photoprotection was lower whereas light‐induced increase in biomass production was higher in RR than in TG, thus making purple basil the more light tolerant. Purple basil appears indeed to display the conservative resource‐use strategy usually observed in highly stress tolerant species. We conclude that the presence of epidermal coumaroyl anthocyanins confers protective benefits under high light, but it is associated with a reduced plasticity to accommodate changing light fluxes as compared with green leaves.     

Structural Determinants of Unique Properties of Human IgG4-Fc

Human IgG4, normally the least abundant of the four subclasses of IgG in serum, displays a number of unique biological properties. It can undergo heavy-chain exchange, also known as Fab-arm exchange, leading to the formation of monovalent but bispecific antibodies, and it interacts poorly with FcγRII and FcγRIII, and complement. These properties render IgG4 relatively “non-inflammatory” and have made it a suitable format for therapeutic monoclonal antibody production. However, IgG4 is also known to undergo Fc-mediated aggregation and has been implicated in auto-immune disease pathology. We report here the high-resolution crystal structures, at 1.9 and 2.35 Å, respectively, of human recombinant and serum-derived IgG4-Fc. These structures reveal conformational variability at the C_H3–C_H3 interface that may promote Fab-arm exchange, and a unique conformation for the FG loop in the C_H2 domain that would explain the poor FcγRII, FcγRIII and C1q binding properties of IgG4 compared with IgG1 and -3. In contrast to other IgG subclasses, this unique conformation folds the FG loop away from the C_H2 domain, precluding any interaction with the lower hinge region, which may further facilitate Fab-arm exchange by destabilisation of the hinge. The crystals of IgG4-Fc also display Fc–Fc packing contacts with very extensive interaction surfaces, involving both a consensus binding site in IgG-Fc at the C_H2–C_H3 interface and known hydrophobic aggregation motifs. These Fc–Fc interactions are compatible with intact IgG4 molecules and may provide a model for the formation of aggregates of IgG4 that can cause disease pathology in the absence of antigen.     

Mechanistic Study of Uba5 Enzyme and the Ufm1 Conjugation Pathway

E1 enzymes activate ubiquitin or ubiquitin-like proteins (Ubl) via an adenylate intermediate and initiate the enzymatic cascade of Ubl conjugation to target proteins or lipids. Ubiquitin-fold modifier 1 (Ufm1) is activated by the E1 enzyme Uba5, and this pathway is proposed to play an important role in the endoplasmic reticulum (ER) stress response. However, the mechanisms of Ufm1 activation by Uba5 and subsequent transfer to the conjugating enzyme (E2), Ufc1, have not been studied in detail. In this work, we found that Uba5 activated Ufm1 via a two-step mechanism and formed a binary covalent complex of Uba5∼Ufm1 thioester. This feature contrasts with the three-step mechanism and ternary complex formation in ubiquitin-activating enzyme Uba1. Uba5 displayed random ordered binding with Ufm1 and ATP, and its ATP-pyrophosphate (PP_i) exchange activity was inhibited by both AMP and PP_i. Ufm1 activation and Uba5∼Ufm1 thioester formation were stimulated in the presence of Ufc1. Furthermore, binding of ATP to Uba5∼Ufm1 thioester was required for efficient transfer of Ufm1 from Uba5 to Ufc1 via transthiolation. Consistent with the two-step activation mechanism, the mechanism-based pan-E1 inhibitor, adenosine 5′-sulfamate (ADS), reacted with the Uba5∼Ufm1 thioester and formed a covalent, tight-binding Ufm1-ADS adduct in the active site of Uba5, which prevented further substrate binding or catalysis. ADS was also shown to inhibit the Uba5 conjugation pathway in the HCT116 cells through formation of the Ufm1-ADS adduct. This suggests that further development of more selective Uba5 inhibitors could be useful in interrogating the roles of the Uba5 pathway in cells.     

Insulin Stimulates Syntaxin4 SNARE Complex Assembly via a Novel Regulatory Mechanism

Insulin stimulates glucose transport into fat and muscle cells by increasing the exocytic trafficking rate of the GLUT4 facilitative glucose transporter from intracellular stores to the plasma membrane. Delivery of GLUT4 to the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for the first time that insulin stimulation causes an increase in syntaxin4-containing SNARE complex formation in adipocytes. Furthermore, we demonstrate that insulin brings about this increase in SNARE complex formation by mobilizing a pool of syntaxin4 held in an inactive state under basal conditions. Finally, we have identified phosphorylation of the regulatory protein Munc18c, a direct target of the insulin receptor, as a molecular switch to coordinate this process. Hence, this report provides molecular detail of how the cell alters membrane traffic in response to an external stimulus, in this case, insulin.     

A Highlights from MBoC Selection: Cdk1 promotes cytokinesis in fission yeast through activation of the septation initiation network

In Schizosaccharomyces pombe, late mitotic events are coordinated with cytokinesis by the septation initiation network (SIN), an essential spindle pole body (SPB)–associated kinase cascade, which controls the formation, maintenance, and constriction of the cytokinetic ring. It is not fully understood how SIN initiation is temporally regulated, but it depends on the activation of the GTPase Spg1, which is inhibited during interphase by the essential bipartite GTPase-activating protein Byr4-Cdc16. Cells are particularly sensitive to the modulation of Byr4, which undergoes cell cycle–dependent phosphorylation presumed to regulate its function. Polo-like kinase, which promotes SIN activation, is partially responsible for Byr4 phosphorylation. Here we show that Byr4 is also controlled by cyclin-dependent kinase (Cdk1)–mediated phosphorylation. A Cdk1 nonphosphorylatable Byr4 phosphomutant displays severe cell division defects, including the formation of elongated, multinucleate cells, failure to maintain the cytokinetic ring, and compromised SPB association of the SIN kinase Cdc7. Our analyses show that Cdk1-mediated phosphoregulation of Byr4 facilitates complete removal of Byr4 from metaphase SPBs in concert with Plo1, revealing an unexpected role for Cdk1 in promoting cytokinesis through activation of the SIN pathway.     

Genetic control of invasive fish: technological options and its role in integrated pest management

Genetic options for the control of invasive fishes were recently reviewed and synthesized at a 2010 international symposium, held in Minneapolis/St. Paul, MN, USA. The only option currently available “off-the-shelf” is triploidy, which can be used to produce sterile males for a release program analogous to those widely and successfully used for biological control of insect pests. However, the Trojan Y and several recombinant options that heritably distort pest population sex ratios are technologically feasible, are at or are close to proof-of-concept stage and are potentially much more effective than sterile male release programs. All genetic options at this stage require prolonged stocking programs to be effective, though gene drive systems are a potential for recombinant approaches. They are also likely to differ in their current degree of social acceptability, with chromosomal approaches (triploidy and Trojan Y) likely to be the most readily acceptable to the public and least likely to require changes in legislative or policy settings to be implemented. Modelling also suggests that the efficacy of any of these genetic techniques is enhanced by, and in turn non-additively enhance, conventional methods of pest fish control.     

Seasonal Patterns in Human A (H5N1) Virus Infection: Analysis of Global Cases

Background

Human cases of highly pathogenic avian influenza (HPAI) A (H5N1) have high mortality. Despite abundant data on seasonal patterns in influenza epidemics, it is unknown whether similar patterns exist for human HPAI H5N1 cases worldwide. Such knowledge could help decrease avian-to-human transmission through increased prevention and control activities during peak periods.

Methods

We performed a systematic search of published human HPAI H5N1 cases to date, collecting month, year, country, season, hemisphere, and climate data. We used negative binomial regression to predict changes in case incidence as a function of season. To investigate hemisphere as a potential moderator, we used AIC and the likelihood-ratio test to compare the season-only model to nested models including a main effect or interaction with hemisphere. Finally, we visually assessed replication of seasonal patterns across climate groups based on the Köppen-Geiger climate classification.

Findings

We identified 617 human cases (611 with complete seasonal data) occurring in 15 countries in Southeast Asia, Africa, and the Middle East. Case occurrence was much higher in winter (n = 285, p = 0.03) than summer (n = 64), and the winter peak occurred across diverse climate groups. There was no significant interaction between hemisphere and season.

Interpretation

Across diverse climates, HPAI H5N1 virus infection in humans increases significantly in winter. This is consistent with increased poultry outbreaks and HPAI H5N1 virus transmission during cold and dry conditions. Prioritizing prevention and control activities among poultry and focusing public health messaging to reduce poultry exposures during winter months may help to reduce zoonotic transmission of HPAI H5N1 virus in resource-limited settings.