The kangaroo's tail propels and powers pentapedal locomotion

When moving slowly, kangaroos plant their tail on the ground in sequence with their front and hind legs. To determine the tail''s role in this ‘pentapedal’ gait, we measured the forces the tail exerts on the ground and calculated the mechanical power it generates. We found that the tail is responsible for as much propulsive force as the front and hind legs combined. It also generates almost exclusively positive mechanical power, performing as much mass-specific mechanical work as does a human leg during walking at the same speed. Kangaroos use their muscular tail to support, propel and power their pentapedal gait just like a leg.     

A novel method to determine the topology of peroxisomal membrane proteins in vivo using the tobacco etch virus protease.

Most proteins essential for the biogenesis of peroxisomes (peroxins) that are identified to date are associated with or are integral components of the peroxisomal membrane. A prerequisite in elucidating their function is to determine their topology in the membrane. We have developed a novel tool to analyze the topology of peroxisomal membrane proteins in the yeast Hansenula polymorpha in vivo using the 27-kDa NIa protease subunit from the tobacco etch virus (TEVp). TEVp specifically cleaves peptides containing the consensus sequence, EXXYXQ downward arrowS (tev). We show that cytosolic TEVp and peroxisomal TEVp.SKL are selectively active on soluble cytosolic and peroxisomal tev-containing proteins in vivo, respectively, without affecting the viability of the yeast cells. The tev sequence was introduced in between the primary sequence of the peroxisomal membrane proteins Pex3p or Pex10p and the reporter protein enhanced green fluorescent protein (eGFP). Co-synthesis of these functional tev-GFP tagged proteins with either cytosolic TEVp or peroxisomal TEVp.SKL revealed that the C termini of Pex3p and Pex10p are exposed to the cytosol. Additional applications of the TEV protease to study peroxisome biogenesis are discussed.     

Effects of obesity and sex on the energetic cost and preferred speed of walking.

The metabolic energy cost of walking is determined, to a large degree, by body mass, but it is not clear how body composition and mass distribution influence this cost. We tested the hypothesis that walking would be most expensive for obese women compared with obese men and normal-weight women and men. Furthermore, we hypothesized that for all groups, preferred walking speed would correspond to the speed that minimized the gross energy cost per distance. We measured body composition, maximal oxygen consumption, and preferred walking speed of 39 (19 class II obese, 20 normal weight) women and men. We also measured oxygen consumption and carbon dioxide production while the subjects walked on a level treadmill at six speeds (0.50-1.75 m/s). Both obesity and sex affected the net metabolic rate (W/kg) of walking. Net metabolic rates of obese subjects were only approximately 10% greater (per kg) than for normal-weight subjects, and net metabolic rates for women were approximately 10% greater than for men. The increase in net metabolic rate at faster walking speeds was greatest in obese women compared with the other groups. Preferred walking speed was not different across groups (1.42 m/s) and was near the speed that minimized gross energy cost per distance. Surprisingly, mass distribution (thigh mass/body mass) was not related to net metabolic rate, but body composition (% fat) was (r2= 0.43). Detailed biomechanical studies of walking are needed to investigate whether obese individuals adopt novel energy saving mechanisms during walking.     

Binding of antimitotic drugs around cysteine residues of tubulin

Two independent approaches provide evidence of cysteine residues in the vicinity of the binding sites of colchicine and vinblastine to tubulin: (1) The reactive bromoacetamide group of the affinity label bromocolchicine covalently binds to cysteine residues of tubulin; (2) vinblastine and colchicine slow down the reaction of DTNB with SH groups of tubulin.     

Cytotoxic T lymphocyte lysis of HTLV-1 infected cells is limited by weak HBZ protein expression,but non-specifically enhanced on induction of Tax expression

Background

Immunogenetic evidence indicates that cytotoxic T lymphocytes (CTLs) specific for the weak CTL antigen HBZ limit HTLV-1 proviral load in vivo, whereas there is no clear relationship between the proviral load and the frequency of CTLs specific for the immunodominant antigen Tax. In vivo, circulating HTLV-1-infected cells express HBZ mRNA in contrast, Tax expression is typically low or undetectable. To elucidate the virus-suppressing potential of CTLs targeting HBZ, we compared the ability of HBZ- and Tax-specific CTLs to lyse naturally-infected cells, by co-incubating HBZ- and Tax-specific CTL clones with primary CD4⁺ T cells from HLA-matched HTLV-1-infected donors. We quantified lysis of infected cells, and tested whether specific virus-induced host cell surface molecules determine the susceptibility of infected cells to CTL-mediated lysis.

Results

Primary infected cells upregulated HLA-A*02, ICAM-1, Fas and TRAIL-R1/2 in concert with Tax expression, forming efficient targets for both HTLV-1-specific CTLs and CTLs specific for an unrelated virus. We detected expression of HBZ mRNA (spliced isoform) in both Tax-expressing and non-expressing infected cells, and the HBZ_26–34 epitope was processed and presented by cells transfected with an HBZ expression plasmid. However, when coincubated with primary cells, a high-avidity HBZ-specific CTL clone killed significantly fewer infected cells than were killed by a Tax-specific CTL clone. Finally, incubation with Tax- or HBZ-specific CTLs resulted in a significant decrease in the frequency of cells expressing high levels of HLA-A*02.

Conclusions

HTLV-1 gene expression in primary CD4⁺ T cells non-specifically increases susceptibility to CTL lysis. Despite the presence of HBZ spliced-isoform mRNA, HBZ epitope presentation by primary cells is significantly less efficient than that of Tax.