Protein stability and conformational rearrangements in lipid bilayers: linear gramicidin, a model system.

The replacement of four tryptophans in gramicidin A by four phenylalanines (gramicidin M) causes no change in the molecular fold of this dimeric peptide in a low dielectric isotropic organic solvent, but the molecular folds are dramatically different in a lipid bilayer environment. The indoles of gramicidin A interact with the anisotropic bilayer environment to induce a change in the molecular fold. The double-helical fold of gramicidin M, as opposed to the single-stranded structure of gramicidin A, is not compatible with ion conductance. Gramicidin A/gramicidin M hybrid structures have also been prepared, and like gramicidin M homodimers, these dimeric hybrids appear to have a double-helical fold, suggesting that a couple of indoles are being buried in the bilayer interstices. To achieve this equilibrium structure (i.e., minimum energy conformation), incubation at 68 degrees C for 2 days is required. Kinetically trapped metastable structures may be more common in lipid bilayers than in an aqueous isotropic environment. Structural characterizations in the bilayers were achieved with solid-state NMR-derived orientational constraints from uniformly aligned lipid bilayer samples, and characterizations in organic solvents were accomplished by solution NMR.     

Mapping Brucellosis Increases Relative to Elk Density Using Hierarchical Bayesian Models

The relationship between host density and parasite transmission is central to the effectiveness of many disease management strategies. Few studies, however, have empirically estimated this relationship particularly in large mammals. We applied hierarchical Bayesian methods to a 19-year dataset of over 6400 brucellosis tests of adult female elk (Cervus elaphus) in northwestern Wyoming. Management captures that occurred from January to March were over two times more likely to be seropositive than hunted elk that were killed in September to December, while accounting for site and year effects. Areas with supplemental feeding grounds for elk had higher seroprevalence in 1991 than other regions, but by 2009 many areas distant from the feeding grounds were of comparable seroprevalence. The increases in brucellosis seroprevalence were correlated with elk densities at the elk management unit, or hunt area, scale (mean 2070 km²; range  = [95–10237]). The data, however, could not differentiate among linear and non-linear effects of host density. Therefore, control efforts that focus on reducing elk densities at a broad spatial scale were only weakly supported. Additional research on how a few, large groups within a region may be driving disease dynamics is needed for more targeted and effective management interventions. Brucellosis appears to be expanding its range into new regions and elk populations, which is likely to further complicate the United States brucellosis eradication program. This study is an example of how the dynamics of host populations can affect their ability to serve as disease reservoirs.     

A cardiac specific analog of angiotensin I potentiated by converting enzyme inhibition

[1-Sarcosine, 7-Alanine] angiotensin I [( 1-Sar, 7-Ala] AI) and closely related analogs were tested for inotropic activity in the isolated cat heart, and for pressor activity in the intact conscious sheep both before and during converting enzyme inhibition (CEI). [1-Sar, 7-Ala] AI exhibited potent inotropic activity but was only weakly pressor. [1-Sar] AI, [1-Sar, 5-Val] AI, [1-Sar, 7-alpha MeAla] AI [1-Sar, 5-Val, 7-NMeAla] AI and [1-Sar, 5-Val, 7-Sar] were all potent agonists in both preparations. The action of [1-Sar, 7-Ala] AI was potentiated by CEI in both the isolated heart and the intact sheep. The activity of the remaining analogs was either partially or completely blocked by CEI. The activity of all analogs was inhibited by AII receptor blockade. These data indicate that the nature of the substitution in position 7 determines the affinity of the analog for converting enzyme. The [7-Ala] substitution appears to decrease the effect of the analog upon vascular receptors.     

Kinesin-14: the roots of reversal

Kinesin-14 motor proteins step towards microtubule minus ends, in the opposite direction to other kinesins. Work on the still-enigmatic kinesin-14 mechanism published in BMC Structural Biology shows that the carboxyl terminus of the motor head undergoes a dock-undock cycle, like that of plus-end-directed kinesins.