Identification of a rice RNA- and microtubule-binding protein as the multifunctional protein, a peroxisomal enzyme involved in the beta -oxidation of fatty acids.

The control of subcellular mRNA localization and translation is often mediated by protein factors that are directly or indirectly associated with the cytoskeleton. We report the identification and characterization of a rice seed protein that possesses both RNA and microtubule binding activities. In vitro UV cross-linking assays indicated that this protein binds to all mRNA sequences tested, although there was evidence for preferential binding to RNAs that contained A-C nucleotide sequence motifs. The protein was purified to homogeneity using a two-step procedure, and amino acid sequencing identified it as the multifunctional protein (MFP), a peroxisomal enzyme known to possess a number of activities involved in the beta-oxidation of fatty acids. The recombinant version of this rice MFP binds to RNA in UV cross-linking and gel mobility shift experiments, co-sediments specifically with microtubules, and possesses at least two enzymatic activities involved in peroxisomal fatty acid beta-oxidation. Taken together these data suggest that MFP has an important role in mRNA physiology in the cytoplasm, perhaps in regulating the localization or translation of mRNAs through an interaction with microtubules, in addition to its peroxisomal function.     

Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women

A study was done to examine the effects of aluminum, magnesium, and boron on major mineral metabolism in postmenopausal women. This communication describes some of the effects of dietary boron on 12 women between the ages of 48 and 82 housed in a metabolic unit. A boron supplement of 3 mg/day markedly affected several indices of mineral metabolism of seven women consuming a low-magnesium diet and five women consuming a diet adequate in magnesium; the women had consumed a conventional diet supplying about 0.25 mg boron/day for 119 days. Boron supplementation markedly reduced the urinary excretion of calcium and magnesium; the depression seemed more marked when dietary magnesium was low. Boron supplementation depressed the urinary excretion of phosphorus by the low-magnesium, but not by the adequate-magnesium, women. Boron supplementation markedly elevated the serum concentrations of 17 beta-estradiol and testosterone; the elevation seemed more marked when dietary magnesium was low. Neither high dietary aluminum (1000 mg/day) nor an interaction between boron and aluminum affected the variables presented. The findings suggest that supplementation of a low-boron diet with an amount of boron commonly found in diets high in fruits and vegetables induces changes in postmenopausal women consistent with the prevention of calcium loss and bone demineralization.     

Solid-phase peptide synthesis: a silver anniversary report

It has been a quarter of a century since Merrifield's initial report on solid-phase peptide synthesis. The field has matured significantly in recent years with a better understanding of the underlying chemistry. This is reflected by new, milder orthogonal protection schemes and more efficient coupling methods, some of which have been incorporated into automated systems. Advances in purification, especially high performance liquid chromatography, have had a major impact. The efficacy of these improvements has been demonstrated by an impressive litany of applications to biological problems.     

Role of solute drag in intestinal transport

This study presents experiments related to the role of solvent drag and solute drag in the transmembrane movement of nonelectrolytes in a perfused rat intestine preparation. Conditions were chosen to simulate the effects of luminal hyperosmolarity on the permeability of tracer solutes. Data are presented on net water flux, transepithelial potentials, and lumen-to-blood and blood-to-lumen tracer solute movements during control electrolyte perfusion and after making the perfusate hyperosmotic. The results indicate that both solvent drag and solute drag can play significant roles in the transepithelial movement of solute and solute permeabilities in the rat ileum preparation. It is suggested that the potential roles of solvent drag and solute drag should be accounted for or considered during the characterization of the mechanisms of biological membrane function.     

Comparative effects of trichothecene mycotoxins on bovine platelet function: Acetyl T-2 toxin,a more potent inhibitor than T-2 toxin

The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10^?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.     

Determination of the structure of the DNA binding domain of gamma delta resolvase in solution.

The DNA binding domain (DBD) of gamma delta resolvase (residues 141-183) is responsible for the interaction of this site-specific DNA recombinase with consensus site DNA within the gamma delta transposable element in Escherichia coli. Based on chemical-shift comparisons, the proteolytically isolated DBD displays side-chain interactions within a hydrophobic core that are highly similar to those of this domain when part of the intact enzyme (Liu T, Liu DJ, DeRose EF, Mullen GP, 1993, J Biol Chem 268:16309-16315). The structure of the DBD in solution has been determined using restraints obtained from 2-dimensional proton NMR data and is represented by 17 conformers. Experimental restraints included 458 distances based on analysis of nuclear Overhauser effect connectivities, 17 phi and chi 1 torsion angles based on analysis of couplings, and 17 backbone hydrogen bonds determined from NH exchange data. With respect to the computed average structure, these conformers display an RMS deviation of 0.67 A for the heavy backbone atoms and 1.49 A for all heavy atoms within residues 149-180. The DBD consists of 3 alpha-helices comprising residues D149-Q157, S162-T167, and R172-N183. Helix-2 and helix-3 form a backbone fold, which is similar to the canonical helix-turn-helix motif. The conformation of the NH2-terminal residues, G141-R148, appears flexible in solution. A hydrophobic core is formed by side chains donated by essentially all hydrophobic residues within the helices and turns. Helix-1 and helix-3 cross with a right-handed folding topology. The structure is consistent with a mechanism of DNA binding in which contacts are made by the hydrophilic face of helix-3 in the major groove and the amino-terminal arm in the minor groove. This structure represents an important step toward analysis of the mechanism of DNA interaction by gamma delta resolvase and provides initial structure-function comparisons among the divergent DBDs of related resolvases and invertases.