Reactions of vanadium(V) complexes of N,N-dimethylhydroxylamine with sulfur-containing ligands: implications for protein tyrosine phosphatase inhibition

 The equilibrium reactions in aqueous solution of the vanadate complex bis(N,N-dimethylhydroxamido)hydroxooxovanadate with dithiothreitol, cysteine and several related compounds have been studied. The highly favoured products form rapidly with displacement of a single dimethylhydroxylamine ligand to form a vanadium-dimethylhydroxylamine-ancillary ligand complex of 1 :>: 1 stoichiometry. The reaction is promoted by the thiol group and requires one additional functional group. Such additional groups include hydroxyl, amino, carboxyl and amido functionalities. The long-term stability of the starting complex compared to the rapid formation of products is interpreted in terms of an associative mechanism for the reaction. The relevance of these findings to the potent inhibition of protein tyrosine phophatases by the bis(dimethylhydroxamido)vanadate complex is discussed. Received: 16 February 1998 / Accepted: 6 July 1998     

Identifying Biologically Meaningful Hot-Weather Events Using Threshold Temperatures That Affect Life-History

Increases in the frequency, duration and intensity of heat waves are frequently evoked in climate change predictions. However, there is no universal definition of a heat wave. Recent, intense hot weather events have caused mass mortalities of birds, bats and even humans, making the definition and prediction of heat wave events that have the potential to impact populations of different species an urgent priority. One possible technique for defining biologically meaningful heat waves is to use threshold temperatures (T_thresh) above which known fitness costs are incurred by species of interest. We set out to test the utility of this technique using T_thresh values that, when exceeded, affect aspects of the fitness of two focal southern African bird species: the southern pied babbler Turdiodes bicolor (T_thresh = 35.5°C) and the common fiscal Lanius collaris (T_thresh = 33°C). We used these T_thresh values to analyse trends in the frequency, duration and intensity of heat waves of magnitude relevant to the focal species, as well as the annual number of hot days (maximum air temperature > T_thresh), in north-western South Africa between 1961 and 2010. Using this technique, we were able to show that, while all heat wave indices increased during the study period, most rapid increases for both species were in the annual number of hot days and in the maximum intensity (and therefore intensity variance) of biologically meaningful heat waves. Importantly, we also showed that warming trends were not uniform across the study area and that geographical patterns in warming allowed both areas of high risk and potential climate refugia to be identified. We discuss the implications of the trends we found for our focal species, and the utility of the T_thresh technique as a conservation tool.     

Kinetics and molecular modelling studies of the inhibition of protein tyrosine phosphatases by N,N-dimethylhydroxylamine complexes of vanadium(V)

 Bis(N,N-dimethylhydroxamido)hydroxooxovanadate and a derivative complex formed with dithiothreitol have been shown to be excellent inhibitors of the function of two protein tyrosine phosphatases, leucocyte antigen related phosphatase (LAR) and protein tyrosine phosphatase-1B (PTP1B). Inhibition constants of 1.0±0.3 μM and 2.3±0.3 μM, respectively, were determined for the inhibition of LAR by the two complexes. The inhibition of PTP1B is not substantially different. Unlike the structurally related hydrogen peroxide complexes of vanadium, these complexes inhibit in a fully reversible manner that is consistent with a non-oxidative process. Molecular modelling studies suggest the main stabilizing interaction is a cyclic H-bonded structure involving the conserved active site aspartate. Hydrophobic stabilization interactions were also suggested. Received: 17 February 1998 / Accepted: 6 July 1998     

Impact of Inactivated Extracellular Proteases on the Modified Flagellin Type III Secretion Pathway of Bacillus halodurans

The flagellin type III secretion pathway of Bacillus halodurans BhFC01 (Δhag) was modified by the inactivation of fliD. An in-frame flagellin gene fusion polypeptide construct was expressed, and the heterologous peptides were secreted as flagellin fusion monomers. The stability of the secreted monomers was significantly enhanced through gene-targeted inactivation of extracellular proteases.