Hunting for alternative disulfide bond formation pathways: endoplasmic reticulum janitor turns professor and teaches a lesson

In this issue of Molecular Cell, Ron and colleagues (Zito et al., 2010b) show that an enzyme responsible for cleaning up hydrogen peroxide in the endoplasmic reticulum can contribute productively to disulfide bond formation.     

Vicinal coupling constants and protein dynamics

The effects of motional averaging on the analysis of vicinal spin-spin coupling constants derived from proton NMR studies of proteins have been examined. Trajectories obtained from molecular dynamics simulations of bovine pancreatic trypsin inhibitor and of hen egg white lysozyme were used in conjunction with an expression for the dependence of the coupling constant on the intervening dihedral angle to calculate the time-dependent behavior of the coupling constants. Despite large fluctuations, the time-average values of the coupling constants are not far from those computed for the average structure in the cases where fluctuations occur about a single potential well. The calculated differences show a high correlation with the variation in the magnitude of the fluctuations of individual dihedral angles. For the cases where fluctuations involve multiple sites, large differences are found between the time-average values and the average structure values for the coupling constants. Comparison of the simulation results with the experimental trends suggests that side chains with more than one position are more common in proteins than is inferred from X-ray results. It is concluded that for the main chain, motional effects do not introduce significant errors where vicinal coupling constants are used in structure determinations; however, for side chains, the motional average can alter deductions about the structure. Accurately measured coupling constants are shown to provide information concerning the magnitude of dihedral angle fluctuations.     

Protector turns predator

Therapy-induced autophagy is recognized as a critical determinant of treatment outcome in cancer patients, primarily as a factor underlying drug resistance. However, recent investigations point toward a context-dependent, death-inducing role for autophagy, the mechanism of which remains largely unknown. Our recent study provides evidence that autophagy can directly mediate cell killing in multiple tumor cell types by facilitating degradation of KRAS/K-Ras, a key survival protein. These findings have broad implications for strategies employing autophagy modulation to target tumor cells.     

Sprinting with banked turns

Bank angle effects can attenuate peak running speed on the order of 10%. Experimental and theoretical results are presented here to quantify this phenomenon over a wide range of bank angles theta b and turn radii R. Experimentally, eleven subjects ran on a 34 m long plywood test track with variable radius and bank angle to sample the (R, theta b) space. From another study, ten subjects are borrowed to examine the theta b = 0 degrees case in greater detail. Various gait parameters were measured from high-speed film, and after parallax correction, compared with the theoretical predictions. The theory is a simple two-parameter constant force model requiring only the effective ankle pulley ratio beta and the runner's top speed vm. A closed-form dimensionless solution is presented for the speed ratio (v/vm) as a function of the radius number (Rg/v2) and the bank angle theta b. Agreement between theory and experiment is limited by experimental scatter. For twenty different subjects and twelve different combinations of R and theta b, the apparent ankle pulley ratio is beta = 0.27 +/- 0.22 based on 128 separate trials. Applications are discussed briefly for the design of indoor and outdoor running tracks. The theory allows a calculation of foot force, bone force, and tendon tension for the general case of arbitrary maximum speed, turn radius and bank angle.     

Stereoselective Microbial Dehalorespiration with Vicinal Dichlorinated Alkanes

The suspected carcinogen 1,2-dichloroethane (1,2-DCA) is the most abundant chlorinated C₂ groundwater pollutant on earth. However, a reductive in situ detoxification technology for this compound does not exist. Although anaerobic dehalorespiring bacteria are known to catalyze several dechlorination steps in the reductive-degradation pathway of chlorinated ethenes and ethanes, no appropriate isolates that selectively and metabolically convert them into completely dechlorinated end products in defined growth media have been reported. Here we report on the isolation of Desulfitobacterium dichloroeliminans strain DCA1, a nutritionally defined anaerobic dehalorespiring bacterium that selectively converts 1,2-dichloroethane and all possible vicinal dichloropropanes and -butanes into completely dechlorinated end products. Menaquinone was identified as an essential cofactor for growth of strain DCA1 in pure culture. Strain DCA1 converts chiral chlorosubstrates, revealing the presence of a stereoselective dehalogenase that exclusively catalyzes an energy-conserving anti mechanistic dichloroelimination. Unlike any known dehalorespiring isolate, strain DCA1 does not carry out reductive hydrogenolysis reactions but rather exclusively dichloroeliminates its substrates. This unique dehalorespiratory biochemistry has shown promising application possibilities for bioremediation purposes and fine-chemical synthesis.     

The lysosome turns fifty

In the course of an investigation aimed at characterizing hepatic glucose 6-phosphatase, the unrelated acid phosphatase of rat liver was serendipitously observed to be latent and particle-bound in freshly prepared homogenates. Experiments designed to elucidate this intriguing finding led, 50 years ago, to the discovery of lysosomes. This could not have happened if strict adherence to a previously set programme had been mandatory.