The phylogeny of the ant tribe Formicini (Hymenoptera: Formicidae) with the description of a new genus

Abstract. The holarctic ant tribe Formicini is revised, the new genus Bajcaridris described, and possible phylogenetic relationships are discussed. The subgenus Iberoformica is synonymized with Formica. A synopsis, diagnosis and keys to the genera are provided.     

世居及移居高原青少年最大有氧能力的特征

本文报道海拔３４１７ｍ和４２８０ｍ地区世居藏族和移居汉族青少年运动状态下心肺功能的对比研究。结果显示：３４１７ｍ和４２８０ｍ世居藏族的最大氧耗量、无氧阈值及最大心输出量都明显大于汉族,血氧饱和度（Ｓａｏ２）随运动负荷的增加而降低。海拔３４１７ｍ藏、汉族的△Ｓａｏ２分别为７．４６％和１０．０３％,４２８０ｍ处为８．５７％和１３．７５％,最大心率随海拔升高而下降。研究提示,藏族青少年有较高的最大有氧能力,反映了他们对低氧环境的适应优势。     

An antibiotic factory caught in action

The synthesis of aromatic polyketides, such as actinorhodin, tetracycline and doxorubicin, begins with the formation of a polyketide chain. In type II polyketide synthases (PKSs), chains are polymerized by the heterodimeric ketosynthase-chain length factor (KS-CLF). Here we present the 2.0-A structure of the actinorhodin KS-CLF, which shows polyketides being elongated inside an amphipathic tunnel approximately 17 A in length at the heterodimer interface. The structure resolves many of the questions about the roles of KS and CLF. Although CLF regulates chain length, it does not have an active site; KS must catalyze both chain initiation and elongation. We provide evidence that the first cyclization of the polyketide occurs within the KS-CLF tunnel. The mechanistic details of this central PKS polymerase could guide biosynthetic chemists in designing new pharmaceuticals and polymers.     

Sex differences in the rate of fatigue development and recovery

Background

Many musculoskeltal injuries in the workplace have been attributed to the repetitive loading of muscle and soft tissues. It is not disputed that muscular fatigue is a risk factor for musculoskeltal injury, however the disparity between gender with respect to muscular fatigability and rate of recovery is not well understood. Current health and safety guidelines do not account for sex differences in fatiguability and may be predisposing one gender to greater risk. The purpose of this study was to quantify the sex differences in fatigue development and recovery rate of lower and upper body musculature after repeated bouts of sustained isometric contractions.

Methods

Twenty-seven healthy males (n = 12) and females (n = 15) underwent bilateral localized fatigue of either the knee extensors (male: n = 8; female: n = 8), elbow flexors (male: n = 8; female: n = 10), or both muscle groups. The fatigue protocol consisted of ten 30-second sub-maximal isometric contractions. The changes in maximum voluntary contraction (MVC), electrically evoked twitches, and motor unit activation (MUA) were assessed along with the ability to control the sustained contractions (SLP) during the fatigue protocol using a mixed four-factor repeated measures ANOVA (gender × side × muscle × time) design with significance set at p < 0.05.

Results

There was a significant loss of MVC, MUA, and evoked twitch amplitude from pre- to post-fatigue in both the arms and legs. Males had greater relative loss of isometric force, a higher rate of fatigue development, and were less capable of maintaining the fatiguing contractions in the legs when compared to the females.

Conclusion

The nature of the induced fatigue was a combination of central and peripheral fatigue that did not fully recover over a 45-minute period. The results appear to reflect sex differences that are peripheral, and partially support the muscle mass hypothesis for explaining differences in muscular fatigue.

     

Structural studies of the spinosyn rhamnosyltransferase, SpnG

Spinosyns A and D (spinosad), like many other complex polyketides, are tailored near the end of their biosyntheses through the addition of sugars. SpnG, which catalyzes their 9-OH rhamnosylation, is also capable of adding other monosaccharides to the spinosyn aglycone (AGL) from TDP-sugars; however, the substitution of UDP-D-glucose for TDP-D-glucose as the donor substrate is known to result in a >60000-fold reduction in k(cat). Here, we report the structure of SpnG at 1.65 ? resolution, SpnG bound to TDP at 1.86 ? resolution, and SpnG bound to AGL at 1.70 ? resolution. The SpnG-TDP complex reveals how SpnG employs N202 to discriminate between TDP- and UDP-sugars. A conformational change of several residues in the active site is promoted by the binding of TDP. The SpnG-AGL complex shows that the binding of AGL is mediated via hydrophobic interactions and that H13, the potential catalytic base, is within 3 ? of the nucleophilic 9-OH group of AGL. A model for the Michaelis complex was constructed to reveal the features that allow SpnG to transfer diverse sugars; it also revealed that the rhamnosyl moiety is in a skew-boat conformation during the transfer reaction.     

The structure of a ketoreductase determines the organization of the beta-carbon processing enzymes of modular polyketide synthases

The structure of the ketoreductase (KR) from the first module of the erythromycin synthase with NADPH bound was solved to 1.79 A resolution. The 51 kDa domain has two subdomains, each similar to a short-chain dehydrogenase/reductase (SDR) monomer. One subdomain has a truncated Rossmann fold and serves a purely structural role stabilizing the other subdomain, which catalyzes the reduction of the beta-carbonyl of a polyketide and possibly the epimerization of an alpha-substituent. The structure enabled us to define the domain boundaries of KR, the dehydratase (DH), and the enoylreductase (ER). It also constrains the three-dimensional organization of these domains within a module, revealing that KR does not make dimeric contacts across the 2-fold axis of the module. The quaternary structure elucidates how substrates are shuttled between the active sites of polyketide synthases (PKSs), as well as related fatty acid synthases (FASs), and suggests how domains can be swapped to make hybrid synthases that produce novel polyketides.     

Catalysis,specificity, and ACP docking site of Streptomyces coelicolor malonyl-CoA:ACP transacylase

Malonyl-CoA:ACP transacylase (MAT), the fabD gene product of Streptomyces coelicolor A3(2), participates in both fatty acid and polyketide synthesis pathways, transferring malonyl groups that are used as extender units in chain growth from malonyl-CoA to pathway-specific acyl carrier proteins (ACPs). Here, the 2.0 A structure reveals an invariant arginine bound to an acetate that mimics the malonyl carboxylate and helps define the extender unit binding site. Catalysis may only occur when the oxyanion hole is formed through substrate binding, preventing hydrolysis of the acyl-enzyme intermediate. Macromolecular docking simulations with actinorhodin ACP suggest that the majority of the ACP docking surface is formed by a helical flap. These results should help to engineer polyketide synthases (PKSs) that produce novel polyketides.     

Relationships in the Drosophila obscura species group, inferred from mitochondrial cytochrome oxidase II sequences

We compare the sequences for the mitochondrial cytochrome oxidase II gene of 13 species of the Drosophila obscura group. The survey includes six members of the D. affinis subgroup, four of the D. pseudoobscura subgroup, and three of the D. obscura subgroup. In all species, the gene is 688 nucleotides in length, encoding a protein of 229 amino acids plus the first position T of the stop codon. The sequences show the typical high-transition bias for closely related species, but that bias is essentially eliminated for species pairs of > 5% sequence divergence. The phylogenetic relationships in the species group are inferred using both neighbor-joining and maximum parsimony. The two procedures give comparable results, showing that the D. affinis and D. pseudoobscura subgroups are monophyletic groupings that appear to have closer affinities to one another than either has to the D. obscura subgroup. We use transversion distances to estimate times of divergence, on the basis of three different estimates of the time of separation of the D. obscura species group from the D. melanogaster group. If that event occurred 35 Mya, then we can estimate the origin of the nearctic forms at approximately 22 Mya and the separation of the D. affinis and D. pseudoobscura subgroups at approximately 17 Mya.