Low-Molecular-Weight, Calcium-Dependent Phospholipase A2Genes Are Linked and Map to Homologous Chromosome Regions in Mouse and Human

The Group IIA phospholipase gene (PLA2G2A) protein coding regions exhibit significant homology with recently described Group IIC (PLA2G2C) and Group V (PLA2GV) genes. All three genes are present in many mammalian species and are expressed in a tissue-specific pattern. Here, we demonstrate in human that they are tightly linked and map to chromosome 1p34–p36.1. We also show that the homologous mouse loci are tightly linked (no observed recombination) on the distal part of chromosome 4, a region exhibiting synteny with human 1p34–p36. Unlike its rodent counterpart, humanPLA2G2Cappears to be a nonfunctional pseudogene.     

Electron tunneling in proteins: role of the intervening medium

Analysis of electron-transfer (ET) kinetics data obtained from experiments on Ru-modified proteins (azurin, cytochrome c, myoglobin) and the bacterial photosynthetic reaction center reveals that distant donor-acceptor electronic couplings depend upon the secondary structure of the intervening polypeptide matrix. The β-sheet azurin structure efficiently and isotropically mediates coupling with an exponential distance-decay constant of 1.1?Å^–1. The experimentally derived distance-decay constant of 1.4?Å^–1 for long-range ET in myoglobin and the reaction center suggests that hydrogen-bond couplings are weaker through α helices than across β sheets. The donor-acceptor interactions of systems with comparable tunneling energies fall into two coupling zones: the β zone (bounded by distance-decay constants of 0.9?and 1.15 Å^–1) includes all the β-sheet (azurin) couplings and all but one coupling in cytochrome c; the α zone (boundaries: 1.25 and 1.6?Å^–1) includes less strongly coupled donor-acceptor pairs in myoglobin and the reaction center as well as a relatively weakly coupled pair in cytochrome c.     

Molecular and phenotypic analysis of the S. cerevisiae MNN10 gene identifies a family of related glycosyltransferases

The Saccharomyces cerevisiae mnn10 mutant is defective in thesynthesis of N-linked oligosaccharides (Ballou et al., 1989).This mutation has no effect on O-linked sugars, but resultsin the accumulation of glycoproteins that contain severely truncatedN-linked outer-chain oligosaccharides. We have cloned the MNN10gene by complementation of the hygromycin B sensitivity conferredby the mutant phenotype. Sequence analysis predicts that Mnn10pis a 46.7 kDa type II membrane protein with structural featurescharacteristic of a glycosyltransferase. Subcellular fractionationdata indicate that most of the Mnn10 protein cofractionateswith Golgi markers and away from markers for the endoplasmicreticulum (ER), suggesting Mnn10p is localized to the Golgicomplex. A comparison of the Mnn10 protein sequence to proteinsin the two different databases identified five proteins thatare homologous to Mnn10p, including a well characterized Schizosaccharomycespombe     

Humpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current

Large, migratory predators are often cited as sentinel species for ecosystem processes and climate‐related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. Documentation of the links between climate variability, ecosystem change and predator dynamics is absent for most top predators. Identifying species that may be useful indicators and elucidating these mechanistic links provides insight into current ecological dynamics and may inform predictions of future ecosystem responses to climatic change. We examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic 20‐year period (1993–2012) in the California Current System (CCS). Humpback whale diets captured two major shifts in oceanographic and ecological conditions in the CCS. Isotopic signatures reflect a diet dominated by krill during periods characterized by positive phases of the North Pacific Gyre Oscillation (NPGO), cool sea surface temperature (SST), strong upwelling and high krill biomass. In contrast, humpback whale diets are dominated by schooling fish when the NPGO is negative, SST is warmer, seasonal upwelling is delayed and anchovy and sardine populations display increased biomass and range expansion. These findings demonstrate that humpback whales trophically respond to ecosystem shifts, and as a result, their foraging behavior is a synoptic indicator of oceanographic and ecological conditions across the CCS. Multi‐decadal examination of these sentinel species thus provides insight into biological consequences of interannual climate fluctuations, fundamental to advancing ecosystem predictions related to global climate change.     

Social selection parapatry in Afrotropical sunbirds

The extent of range overlap of incipient and recent species depends on the type and magnitude of phenotypic divergence that separates them, and the consequences of phenotypic divergence on their interactions. Signal divergence by social selection likely initiates many speciation events, but may yield niche‐conserved lineages predisposed to limit each others’ ranges via ecological competition. Here, we examine this neglected aspect of social selection speciation theory in relation to the discovery of a nonecotonal species border between sunbirds. We find that Nectarinia moreaui and Nectarinia fuelleborni meet in a ～6 km wide contact zone, as estimated by molecular cline analysis. These species exploit similar bioclimatic niches, but sing highly divergent learned songs, consistent with divergence by social selection. Cline analyses suggest that within‐species stabilizing social selection on song‐learning predispositions maintains species differences in song despite both hybridization and cultural transmission. We conclude that ecological competition between moreaui and fuelleborni contributes to the stabilization of the species border, but that ecological competition acts in conjunction with reproductive interference. The evolutionary maintenance of learned song differences in a hybrid zone recommend this study system for future studies on the mechanisms of learned song divergence and its role in speciation.     

The interplay between effector binding and allostery in an engineered protein switch

The protein design rules for engineering allosteric regulation are not well understood. A fundamental understanding of the determinants of ligand binding in an allosteric context could facilitate the design and construction of versatile protein switches and biosensors. Here, we conducted extensive in vitro and in vivo characterization of the effects of 285 unique point mutations at 15 residues in the maltose‐binding pocket of the maltose‐activated β‐lactamase MBP317‐347. MBP317‐347 is an allosteric enzyme formed by the insertion of TEM‐1 β‐lactamase into the E. coli maltose binding protein (MBP). We find that the maltose‐dependent resistance to ampicillin conferred to the cells by the MBP317‐347 switch gene (the switch phenotype) is very robust to mutations, with most mutations slightly improving the switch phenotype. We identified 15 mutations that improved switch performance from twofold to 22‐fold, primarily by decreasing the catalytic activity in the absence of maltose, perhaps by disrupting interactions that cause a small fraction of MBP in solution to exist in a partially closed state in the absence of maltose. Other notable mutations include K15D and K15H that increased maltose affinity 30‐fold and Y155K and Y155R that compromised switching by diminishing the ability of maltose to increase catalytic activity. The data also provided insights into normal MBP physiology, as select mutations at D14, W62, and F156 retained high maltose affinity but abolished the switch's ability to substitute for MBP in the transport of maltose into the cell. The results reveal the complex relationship between ligand binding and allostery in this engineered switch.