Stereoselective binding of an enantiomeric pair of stromelysin-1 inhibitors caused by conformational entropy factors.

Isothermal titration calorimetry was used to analyze the binding of an enantiomeric pair of inhibitors to the stromelysin-1 catalytic domain. Differences in binding affinity are attributable to different conformational entropy penalties suffered upon binding. Two possible explanations for these differences are proposed.

Effects of vomitoxin ingestion on murine models for systemic lupus erythematosus.

Dietary exposure to the trichothecene vomitoxin (VT) results in reduced body weight gain, elevated serum IgA, terminal differentiation of Peyer's patch B cells to IgA secreting plasma cells haematuria, and increased kidney mesangial IgA accumulation in B6C3F1 mice and other inbred strains. These effects closely mimic a human autoimmune-like kidney disease known as IgA nephropathy. Using NZBW/F1, MRL/lpr, and BXSB mouse strains as models of systemic lupus erythematosus, we assessed whether consumption of diet containing 5 ppm or 10 ppm VT will similarly affect mice genetically prone to autoimmunity. Reduced weight gains were seen in NZBW/F1 and MRL/lpr mice fed both doses of VT within 2-3 weeks. In contrast, VT had little effect on weight gain by BXSB mice. Serum Ig levels in all three strains generally did not differ from control mice. Haematuria was significantly increased when all three strains were fed VT. In NZBW/F1 Peyer's patch cultures stimulated with lipopolysaccharide (LPS), prior VT exposure significantly increased the IgG and IgM secretion but had no effect on IgA. In MRL/lpr Peyer's patch cultures stimulated with LPS, VT exposure increased IgA secretion but not IgM or IgG. BXSB Peyer's patch cultures prepared from VT treatment groups produced significantly more IgA than controls when cultured with LPS or Concanavalin A. Whereas mesangial deposition of IgA and IgG was significantly lower in the treatment groups of NZBW/F1 and MRL/lpr mice compared with control, BXSB mice had significantly higher IgA, IgG, and complement (C3) deposition when fed VT. The results suggest that although dietary VT differentially affected mice with aberrant immune systems, these strains did not appear to be any more sensitive to the mycotoxin than were more immunologically robust inbred strains.

Effects of intermittent vomitoxin exposure on body weight, immunoglobulin levels and haematuria in the B6C3F1 mouse.

Continuous dietary exposure of female B6C3F1 mice to the trichothecene vomitoxin (VT) results in reduced body weight gain, elevated production of serum immunoglobulin A (IgA), kidney mesangial IgA deposition and glomerulonephritis. To assess whether intermittent consumption of dietary VT, as might occur during natural animal and human exposures, has similar effects to those for continuous consumption, a comparison was made between two schedules of dietary exposure. Female B6C3F1 mice were fed for 13 weeks with either a semipurified AIN-76A diet containing 20 ppm VT continuously or with 20 ppm VT intermittently (every other week). The effect these diets had on body weight gain, serum immunoglobulin (Ig) profile, mesangial Ig deposition and haematuria were assessed and compared with each other as well as with mice fed a control diet. Reduced body weight gains in the treatment groups were seen as early as 2 weeks. After week 4, the mean body weight of the intermittent group appeared higher than the continuous group during the weeks when it was fed a control diet, but dropped to continuous group levels during the weeks they were fed VT. Serum IgA levels in the intermittent group remained at control levels and were significantly lower than the continuous group during the course of the study. In contrast, serum IgG and serum immunoglobulin M (IgM) levels for the intermittent and continuous groups were significantly decreased compared with control. Mesangial IgA deposition was significantly lower in the intermittent group compared with the continuous group, and had levels comparable to mice on the control diet. Haematuria was significantly greater in both treatment groups compared with control at weeks 5 and 13 when the intermittent group was fed VT containing diet, but haematuria in the intermittent group dissipated at week 10 when it was fed control diet. The results presented here suggest that the type of dietary exposure regimen is critical in determining the extent of toxic effects induced by VT. Thus, when animal models are used for assessing the toxic effects of mycotoxins, it may be useful to consider the effects of intermittent and sporadic exposure.

Application of electrospray ionization mass spectrometry for studying human immunodeficiency virus protein complexes.

Mass spectrometry (MS) with electrospray ionization (ESI) has shown utility for studying noncovalent protein complexes, as it offers advantages in sensitivity, speed, and mass accuracy. The stoichiometry of the binding partners can be easily deduced from the molecular weight measurement. In many examples of protein complexes, the gas phase-based measurement is consistent with the expected solution phase binding characteristics. This quality suggests the utility of ESI-MS for investigating solution phase molecular interactions. Complexes composed of proteins from the human immunodeficiency virus (HIV) have been studied using ESI-MS. Multiply charged protein dimers from HIV integrase catalytic core (F185K) and HIV protease have been observed. Furthermore, the ternary complex between HIV protease dimer and inhibitor pepstatin A was studied as a function of solution pH. Zinc binding to zinc finger-containing nucleocapsid protein (NCp7) and the NCp7-psi RNA 1:1 stoichiometry complex was also studied by ESI-MS. No protein-RNA complex was observed in the absence of zinc, consistent with the role of the zinc finger motifs for RNA binding.