Antarctica on foot: the energy expended to walk,ski and man-haul

Polar exploration often involves travelling on foot and thus is physically intensive, with long-term excursions typically resulting in weight loss. Few studies have investigated the energy expended under such circumstances. Here, we present a range of prediction equations for estimating metabolic rate from heart rate or accelerometry data for specific activities including skiing and man-hauling which can be applied to either short- or long-term excursions. We also use some of these equations to estimate the energy expended undertaking various activities by a team of explorers while attempting to traverse the Antarctic continent during the austral winter of 2013 (as part of the White Mars Project during The Coldest Journey). Calibration equations based on either accelerometry data (from which overall dynamic body acceleration, ODBA, is derived) or heart rate showed good relationships with rate of oxygen consumption, particularly when person height was included. Periods of skiing and man-hauling on The Coldest Journey were estimated to be more energetically demanding (30.0 and 31.1 kJ min^?1, respectively) than walking (24.9 kJ min^?1), or other outdoor work (21.9 kJ min^?1). Estimates of energy expenditure during The Coldest Journey were similar to measures obtained in previous, comparative scenarios. We hope that future expeditions to Antarctica will use these prediction equations to further our understanding of the energy costs of exploring Antarctica and the nutritional requirements needed to guard against emaciation.     

Glycosylation genes expressed in seam cells determine complex surface properties and bacterial adhesion to the cuticle of Caenorhabditis elegans

The surface of the nematode Caenorhabditis elegans is poorly understood but critical for its interactions with the environment and with pathogens. We show here that six genes (bus-2, bus-4, and bus-12, together with the previously cloned srf-3, bus-8, and bus-17) encode proteins predicted to act in surface glycosylation, thereby affecting disease susceptibility, locomotory competence, and sexual recognition. Mutations in all six genes cause resistance to the bacterial pathogen Microbacterium nematophilum, and most of these mutations also affect bacterial adhesion and biofilm formation by Yersinia species, demonstrating that both infection and biofilm formation depend on interaction with complex surface carbohydrates. A new bacterial interaction, involving locomotory inhibition by a strain of Bacillus pumilus, reveals diversity in the surface properties of these mutants. Another biological property--contact recognition of hermaphrodites by males during mating--was also found to be impaired in mutants of all six genes. An important common feature is that all are expressed most strongly in seam cells, rather than in the main hypodermal syncytium, indicating that seam cells play the major role in secreting surface coat and consequently in determining environmental interactions. To test for possible redundancies in gene action, the 15 double mutants for this set of genes were constructed and examined, but no synthetic phenotypes were observed. Comparison of the six genes shows that each has distinctive properties, suggesting that they do not act in a linear pathway.     

A survey of integral α-helical membrane proteins

Membrane proteins serve as cellular gatekeepers, regulators, and sensors. Prior studies have explored the functional breadth and evolution of proteins and families of particular interest, such as the diversity of transport-associated membrane protein families in prokaryotes and eukaryotes, the composition of integral membrane proteins, and family classification of all human G-protein coupled receptors. However, a comprehensive analysis of the content and evolutionary associations between membrane proteins and families in a diverse set of genomes is lacking. Here, a membrane protein annotation pipeline was developed to define the integral membrane genome and associations between 21,379 proteins from 34 genomes; most, but not all of these proteins belong to 598 defined families. The pipeline was used to provide target input for a structural genomics project that successfully cloned, expressed, and purified 61 of our first 96 selected targets in yeast. Furthermore, the methodology was applied (1) to explore the evolutionary history of the substrate-binding transmembrane domains of the human ABC transporter superfamily, (2) to identify the multidrug resistance-associated membrane proteins in whole genomes, and (3) to identify putative new membrane protein families.     

Heterogeneity in MT1-MMP activity with ischemia-reperfusion and previous myocardial infarction: relation to regional myocardial function

After a myocardial infarction (MI), an episode of ischemia-reperfusion (I/R) can result in a greater impairment of left ventricular (LV) regional function (LVRF) than that caused by an initial I/R episode in the absence of MI. Membrane type-I matrix metalloproteinase (MT1-MMP) proteolytically processes the myocardial matrix and is upregulated in LV failure. This study tested the central hypothesis that a differential induction of MT1-MMP occurs and is related to LVRF after I/R in the context of a previous MI. Pigs with a previous MI [3 wk postligation of the left circumflex artery (LCx)] or no MI were randomized to undergo I/R [60-min/120-min left anterior descending coronary artery (LAD) occlusion] or no I/R as follows: no MI and no I/R (n = 6), no MI and I/R (n = 8), MI and no I/R (n = 8), and MI and I/R (n = 8). Baseline LVRF (regional stroke work, sonomicrometry) was lower in the LAD region in the MI group compared with no MI (103 ± 12 vs. 188 ± 26 mmHg·mm, P < 0.05) and remained lower with peak ischemia (35 ± 8 vs. 88 ± 17 mmHg·mm, P < 0.05). Using a novel interstitial microdialysis method, MT1-MMP was directly measured and was over threefold higher in the LCx region and over twofold higher in the LAD region in the MI group compared with the no MI group at baseline. MT1-MMP fluorogenic activity was persistently elevated in the LCx region in the MI and I/R group but remained unchanged in the LAD region. In contrast, no changes in MT1-MMP occurred in the LCx region in the no MI and I/R group but increased in the LAD region. MT1-MMP mRNA was increased by over threefold in the MI region in the MI and I/R group. In conclusion, these findings demonstrate that a heterogeneous response in MT1-MMP activity likely contributes to regional dysfunction with I/R and that a subsequent episode of I/R activates a proteolytic cascade within the MI region that may contribute to a continued adverse remodeling process.     

Extended type-1 chain glycosphingolipid antigens. Isolation and characterization of trifucosyl-Leb antigen (III4V4VI2Fuc3Lc6).

A Lewis-b-active glycosphingolipid containing a repetitive type-1 chain carbohydrate core was isolated from human colonic adenocarcinoma cell line Colo205. This glycosphingolipid was purified by HPLC and preparative high-performance thin-layer chromatography and its structure elucidated by positive-ion fast-atom-bombardment mass spectrometry with collision-induced disassociation, 1H-NMR spectroscopy and methylation analysis. The glycosphingolipid was found to be a trifucosylated derivative of this novel carbohydrate core, having the following structure: [formula; see text].     

Characterization of the 23 S ribosomal RNA m5U1939 methyltransferase from Escherichia coli.

An Escherichia coli open reading frame, ygcA, was identified as a putative 23 S ribosomal RNA 5-methyluridine methyltransferase (Gustafsson, C., Reid, R., Greene, P. J., and Santi, D. V. (1996) Nucleic Acids Res. 24, 3756-3762). We have cloned, expressed, and purified the 50-kDa protein encoded by ygcA. The purified enzyme catalyzed the AdoMet-dependent methylation of 23 S rRNA but did not act upon 16 S rRNA or tRNA. A high performance liquid chromatography-based nucleoside analysis identified the reaction product as 5-methyluridine. The enzyme specifically methylated U1939 as determined by a nuclease protection assay and by methylation assays using site-specific mutants of 23 S rRNA. A 40-nucleotide 23 S rRNA fragment (nucleotide 1930--1969) also served as an efficient substrate for the enzyme. The apparent K(m) values for the 40-mer RNA oligonucleotide and AdoMet were 3 and 26 microm, respectively, and the apparent k(cat) was 0.06 s(-1). The enzyme contains two equivalents of iron/monomer and has a sequence motif similar to a motif found in iron-sulfur proteins. We propose to name this gene rumA and accordingly name the protein product as RumA for RNA uridine methyltransferase.     

Plastic adaptation toward mutations in proteins: structural comparison of thymidylate synthases

The structure of thymidylate synthase (TS) from Escherichia coli was solved from cubic crystals with a = 133 A grown under reducing conditions at pH 7.0, and refined to R = 22% at 2.1 A resolution. The structure is compared with that from Lactobacillus casei solved to R = 21% at 2.3 A resolution. The structures are compared using a difference distance matrix, which identifies a common core of residues that retains the same relationship to one another in both species. After subtraction of the effects of a 50 amino acid insert present in Lactobacillus casei, differences in position of atoms correlate with temperature factors and with distance from the nearest substituted residue. The dependence of structural difference on thermal factor is parameterized and reflects both errors in coordinates that correlate with thermal factor, and the increased width of the energy well in which atoms of high thermal factor lie. The dependence of structural difference on distance from the nearest substitution also depends on thermal factors and shows an exponential dependence with half maximal effect at 3.0 A from the substitution. This represents the plastic accommodation of the protein which is parameterized in terms of thermal B factor and distance from a mutational change.