Thermodynamics and mechanism of alpha helix initiation in alanine and valine peptides

We used molecular dynamics simulations to study the folding/unfolding of one of turn of an alpha helix in Ac-(Ala)3-NHMe and Ac-(Val)3-NHMe. Using specialized sampling techniques, we computed free energy surfaces as functions of a conformational coordinate that corresponds to alpha helices at small values and to extended conformations at large values. Analysis of the peptide conformations populated during the simulations showed that alpha helices, reverse turns, and extended conformations correspond to minima on the free energy surfaces of both peptides. The free energy difference between alpha helix and extended conformations, determined from the equilibrium constants for helix unfolding, is approximately -1 kcal/mol for Ac-(Ala)3-NHMe and -5 kcal/mol for Ac-(Val)3-NHMe. The mechanism observed in our simulations, which includes reverse turns as important intermediates along the helix folding/unfolding pathway, is consistent with a mechanism proposed previously. Our results predict that both peptides (but especially the Ala peptide) have a much larger equilibrium constant for helix initiation than is predicted by the helix-coil transition theory with the host-guest parameters. We also predict a much greater difference in the equilibrium constants than the theory predicts. Insofar as helix initiation is concerned, our results suggest that the large difference between the helical propensities of Ala and Val cannot be explained by simple concepts such as side-chain rotamer restriction or unfavorable steric interactions. Rather, the origin of the difference appears to be quite complicated because it involves subtle differences in the solvation of the two peptides. The two peptides have similar turn-extended equilibria but very different helix-turn equilibria, and the difference in helical propensities reflects the fact that the helix-turn equilibrium strongly favors the turns in Ac-(Val)3-NHMe, while it favors the helices in Ac-(Ala)3-NHMe. We also computed thermodynamic decompositions of the free energy surfaces, and these revealed that the helix-turn equilibria are vastly different primarily because the changes in peptide-water interactions that accompany helix-to-turn conformational changes are qualitatively different for the two peptides.     

Methylprednisolone restores sensitivity to beta-adrenergic agonists in Basenji-Greyhound dogs.

This study investigated the effect of chronic methylprednisolone treatment on the ability of albuterol and aminophylline to inhibit methacholine-induced airway constriction in Basenji-Greyhound (BG) dogs in vivo. Pulmonary responsiveness to methacholine was measured in five untreated BG dogs and in the same dogs pretreated with albuterol or aminophylline (which has been shown in this model to release endogenous catecholamines). Each dog was studied before, during, and after daily subcutaneous methylprednisolone for 6 wk. Changes in pulmonary resistance and dynamic compliance with methacholine aerosol challenge were measured. Neither baseline pulmonary function nor pulmonary responsiveness to aerosolized methacholine was significantly altered by albuterol, aminophylline, or chronic methylprednisolone administration alone. However, pretreatment with albuterol or aminophylline significantly attenuated airway responses to methacholine in BG dogs chronically receiving methylprednisolone. Because the reduced sensitivity to albuterol and aminophylline was restored by chronic methylprednisolone treatment, we conclude that at least part of the beneficial effects of corticosteroids on airways in BG dogs is through modulation of beta-adrenergic function.     

Properties of the foot inhibitor from hydra

Summary A substance was isolated from crude extracts of hydra that inhibits foot regeneration. This substance, the foot inhibitor, has a molecular weight of 500 daltons. It is a hydrophilic molecule, slightly basic in character and it has no peptide bonds. The pruified substance acts specifically and at concentrations lower than 10^–7 M. At this low concentration only foot and not head regeneration is inhibited. Hydra are sensitive to purified foot inhibitor between the second and eight hour after initiation of foot regeneration by cutting. In normal animals the foot inhibitor is most likely produced by nerve cells. A substance with similar biological and physico-chemical properties is found in other coelenterates.     

A new species of Eugenia (Myrtaceae) from Venezuela

Eugenia mcvaughii is described from a forest remnant of the Jardin Botánico of Caracas, Venezuela. Found also in the hills adjacent to Caracas, it may be considered as an endemic species of the Interior Coastal Cordillera.     

Heavy metal-nucleoside interactions. Binding of methylmercury(II) to inosine and catalysis of the isotopic exchange of the C-8 hydrogen studied by 1-H nuclear magnetic resonance and raman difference spectrophotometry.

Raman difference spectrophotometry reveals that CH3HgII binds quantitatively to N(1) of inosine at pH 8, substituting for the proton. When N(1) is saturated, binding occurs at a second site. Measurements of the 1-H nuclear magnetic resonance spectra of both inosine and of CH3Hg-II are in agreement with the N(1) binding and indicate that the second site for mercuriation is N(7). This second binding reaction is observed to increase the rate of exchange of the C(8) hydrogen with solvent, consistent with results observed for alkylation at N(7). Coordination of the electrophilic CH3Hg-II to N(7) increases the acidity of H(8), facilitating OHminus--catalyzed proton abstraction and reprotonation by themedium. For comparison, the reaction of CH3Hg-II with [8-2-H]inosine has been studied. Displacement of the N(1) hydrogen upon mercuriation of inosine causes a significant electron delocalization into the ring, increasing the basicity of N(7), and accounting for the synergic effect in metal binding observed originally by Simpson. In contrast, 1-methylinosine interacts only slightly with CH3Hg-II at pH 8. Coordination appears to be at N(7), since H(8) again is observed to exchange rapidly with solvent protons. In acidic solution, pH less than 2, binding to inosine is almost quantitative and exclusively to N(7). The behavior of CH3Hg-II is compared with that of Pt(II) and with Ni(II), Co(II), AND Zn(II). A brief comparison is made among ultraviolet absorption spectrophotometry, nuclear magnetic resonance (NMR), and Raman difference spectrophotometry for studying reactions of nucleosides and nucleotides.     

Failla Memorial lecture. The future of heavy-ion science in biology and medicine

Interplanetary space contains fluxes of fast moving atomic nuclei. The distribution of these reflects the atomic composition of the universe, and such particles may pose limitations for space flight and for life in space. Over the past 50 years, since the invention of Ernest Lawrence's cyclotron, advances in accelerator technology have permitted the acceleration of charged nuclei to very high velocities. Currently, beams of any stable isotope species up to uranium are available at kinetic energies of several hundred MeV/nucleon at the Berkeley Bevalac. Recently, new areas of particle physics research relating to the mechanisms of spallation and fission have opened up for investigation, and it is now realistic to search for nuclear super-dense states that might be produced in heavy nuclear collisions. The heavy ions hold interest for a broad spectrum of research because of their effectiveness in producing a series of major lesions in DNA along single particle tracks and because of the Bragg depth ionization properties that allow the precise deposition of highly localized doses deep in the human body. Individual heavy ions can also interrupt the continuity of membraneous regions in cells. Heavy ions, when compared to low-LET radiation, have increased effectiveness for mammalian cell lethality, chromosome mutations, and cell transformation. The molecular mechanisms are not completely understood but appear to involve fragmentation and reintegration of DNA. Cells attempt to repair these lesions, and many of the deleterious effects are due to misrepair or misrejoining of DNA. Heavy ions do not require the presence of oxygen for producing their effects, and hypoxic cells in necrotic regions have nearly the same sensitivity as cells in well-oxygenated tissues. Heavy ions are effective in delaying or blocking the cell division process. Heavy ions are also strong enhancers of viral-induced cell transformation, a process that requires integration of foreign DNA. Some cell lines, known to be radioresistant to X rays, have exhibited greater sensitivity to heavy ions. These radiobiological properties, combined with the ability to deliver highly localized internal doses, make accelerated heavy ions potentially important radiotherapeutic tools. Other novel approaches include the utilization of radioactive heavy beams as instant tracers. Heavy-ion radiography and microscopy respond to delicate changes in tissue electron density. Dose localization with helium ions has achieved excellent results for pituitary tumors, tumors adjacent to the spinal cord, and ocular melanomas. We are working on adapting silicon- and neon-ion beams for controlled therapy studies.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cortactin Controls Surface Expression of the Voltage-gated Potassium Channel KV10.1

K_V10.1 is a voltage-gated potassium channel aberrantly expressed in many cases of cancer, and participates in cancer initiation and tumor progression. Its action as an oncoprotein can be inhibited by a functional monoclonal antibody, indicating a role for channels located at the plasma membrane, accessible to the antibody. Cortactin is an actin-interacting protein implicated in cytoskeletal architecture and often amplified in several types of cancer. In this study, we describe a physical and functional interaction between cortactin and K_V10.1. Binding of these two proteins occurs between the C terminus of K_V10.1 and the proline-rich domain of cortactin, regions targeted by many post-translational modifications. This interaction is specific for K_V10.1 and does not occur with K_V10.2. Cortactin controls the abundance of K_V10.1 at the plasma membrane and is required for functional expression of K_V10.1 channels.