Group-selective reagent modification of the sodium- and chloride-coupled glycine transporter under native and reconstituted conditions.

Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein.     

The antigen-antibody interaction algebraically interpreted as a relational process.

The antigen-antibody interaction occurring previous to the triggering of the immunological response is analyzed as a relational process in terms of lattices. Accordingly, this process is expressed as a lattice belonging to a pseudo-Boolean algebraic variety. The Heyting arrow operation, which appears in this kind of algebra, is used to analyze behaviors between non-comparable biological states expressed by the lattice. The resulting states coming from the arrows are connected with the influence of increasing and decreasing energies involved in the linking process.     

Hypermodified nucleoside carboxyl group as a target site for specific tRNA modification

The free carboxyl group of hypermodified nucleosides N6-methyl-N6-(threoninocarbonyl)adenosine (mt6A37) and 3-(3-amino-3-carboxypropyl)uridine (acp3U20:1) in tRNAmMet (yellow lupine), and N6-(threoninocarbonyl)adenosine (t6A37) in tRNAiMet (yellow lupine) can be converted quantitatively and under very mild conditions into the respective anilides in a reaction with aniline and a water-soluble carbodiimide. The tRNA reactions proceed with rates very similar to that reported previously for t6A nucleoside. Detailed analysis of the products of tRNA modification with [3H]aniline on tRNA (chromatography on BD-DEAE-cellulose), oligonucleotide (polyacrylamide gel electrophoresis) and nucleoside (HPLC on Aminex A6) levels clearly indicates that only the hypermodified nucleoside residues undergo the reaction. The site of modification is confirmed for mono-modified (at mt6A37) and bis-modified (at mt6A37 and acp3U20:1) tRNAmMet, and for mono-modified (at t6A37) tRNAiMet by sequence analysis using 5'end 32P-labeled tRNAs. The modification procedure seems to be universally applicable for all hypermodified nucleosides bearing a free carboxyl group and for different amine reagents designed for the studies on tRNA function.     

Apical Scaffolding Protein NHERF2 Modulates the Localization of Alternatively Spliced Plasma Membrane Ca2+ Pump 2B Variants in Polarized Epithelial Cells

The membrane localization of the plasma membrane Ca²⁺-ATPase isoform 2 (PMCA2) in polarized cells is determined by alternative splicing; the PMCA2w/b splice variant shows apical localization, whereas the PMCA2z/b and PMCA2x/b variants are mostly basolateral. We previously reported that PMCA2b interacts with the PDZ protein Na⁺/H⁺ exchanger regulatory factor 2 (NHERF2), but the role of this interaction for the specific membrane localization of PMCA2 is not known. Here we show that co-expression of NHERF2 greatly enhanced the apical localization of GFP-tagged PMCA2w/b in polarized Madin-Darby canine kidney cells. GFP-PMCA2z/b was also redirected to the apical membrane by NHERF2, whereas GFP-PMCA2x/b remained exclusively basolateral. In the presence of NHERF2, GFP-PMCA2w/b co-localized with the actin-binding protein ezrin even after disruption of the actin cytoskeleton by cytochalasin D or latrunculin B. Surface biotinylation and fluorescence recovery after photobleaching experiments demonstrated that NHERF2-mediated anchorage to the actin cytoskeleton reduced internalization and lateral mobility of the pump. Our results show that the specific interaction with NHERF2 enhances the apical concentration of PMCA2w/b by anchoring the pump to the apical membrane cytoskeleton. The data also suggest that the x/b splice form of PMCA2 contains a dominant lateral targeting signal, whereas the targeting and localization of the z/b form are more flexible and not fully determined by intrinsic sequence features.     

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.     

Effect of neurectomy on nuclease activity in skeletal muscles of rats

Author followed up the activity of the three enzymes involved in the catabolism of nucleic acids--acid deoxyribonulease (DNase II), alkaline ribonuclease (RNase I), and acid ribonuclease (RNase II)--in the denervated gastrocnemius and soleus muscles of rats for 28 postoperative days. The activity of both acid nucleases increased in both types of denervated muscles, compared with the respective controls. Up to the 14th postoperative day, the activity excess of both acid nucleases was more significant in the m. gastrocnemius than in the m. soleus. The RNase I ran below the control activity during the whole period in the m. soleus and up to the 14th day in the m. gastrocnemius. The role of nucleases and nuclease inhibitors in the changes of nucleic acid catabolism in neurogenic muscular atrophies is discussed.     

DnaB proteolysis in vivo regulates oligomerization and its localization at oriC in Bacillus subtilis

Initiation of bacterial DNA replication at oriC is mediated by primosomal proteins that act cooperatively to melt an AT-rich region where the replicative helicase is loaded prior to the assembly of the replication fork. In Bacillus subtilis, the dnaD, dnaB and dnaI genes are essential for initiation of DNA replication. We established that their mRNAs are maintained in fast growing asynchronous cultures. DnaB is truncated at its C-terminus in a growth phase-dependent manner. Proteolysis is confined to cytosolic, not to membrane-associated DnaB, and affects oligomerization. Truncated DnaB is depleted at the oriC relative to the native protein. We propose that DNA-induced oligomerization is essential for its action at oriC and proteolysis regulates its localization at oriC. We show that DnaB has two separate ssDNA-binding sites one located within residues 1–300 and another between residues 365–428, and a dsDNA-binding site within residues 365–428. Tetramerization of DnaB is mediated within residues 1–300, and DNA-dependent oligomerization within residues 365–428. Finally, we show that association of DnaB with the oriC is asymmetric and extensive. It encompasses an area from the middle of dnaA to the end of yaaA that includes the AT-rich region melted during the initiation stage of DNA replication.     

On the anatomical definition of arterial networks in blood flow simulations: comparison of detailed and simplified models

Biomechanics and Modeling in Mechanobiology - The goal of this work is to assess the impact of vascular anatomy definition degree in the predictions of blood flow models of the arterial network. To...