Class sigma glutathione transferase unfolds via a dimeric and a monomeric intermediate: impact of subunit interface on conformational stability in the superfamily

Solvent-induced equilibrium unfolding of a homodimeric class sigma glutathione transferase (GSTS1-1, EC 2.5.1.18) was characterized by tryptophan fluorescence, anisotropy, enzyme activity, 8-anilino-1-naphthalenesulfonate (ANS) binding, and circular dichroism. Urea induces a triphasic unfolding transition with evidence for two well-populated thermodynamically stable intermediate states of GSTS1-1. The first unfolding transition is protein concentration independent and involves a change in the subunit tertiary structure yielding a partially active dimeric intermediate (i.e., N2 left and right arrow I2). This is followed by a protein concentration dependent step in which I2 dissociates into compact inactive monomers (M) displaying enhanced hydrophobicity. The third unfolding transition, which is protein concentration independent, involves the complete unfolding of the monomeric state. Increasing NaCl concentrations destabilize N2 and appear to shift the equilibrium toward I2 whereas the stability of the monomeric intermediate M is enhanced. The binding of substrate or product analogue (i.e., glutathione or S-hexylglutathione) to the protein's active site stabilizes the native dimeric state (N2), causing the first two unfolding transitions to shift toward higher urea concentrations. The stability of M was not affected. The data implicate a region at/near the active site in domain I (most likely alpha-helix 2) as being highly unstable/flexible which undergoes local unfolding, resulting initially in I2 formation followed by a disruption in quaternary structure to a monomeric intermediate. The unfolding/refolding pathway is compared with those observed for other cytosolic GSTs and discussed in light of the different structural features at the subunit interfaces, as well as the evolutionary selection of this GST as a lens crystallin.     

Molecular basis and species specificity of high affinity binding of vasoactive intestinal polypeptide by the rat secretin receptor

The affinity and specificity of the binding interaction between ligands and their receptors are key for appropriate hormonal regulation of target tissues. However, it is now apparent that vasoactive intestinal polypeptide (VIP) binds to the rat secretin receptor with similar affinity to that for its natural ligand, secretin (Holtmann et al., 1995). In this report, we establish that this is not a characteristic of the human secretin receptor, and use rat-human secretin receptor chimeras, site mutants and truncated receptor constructs to establish the molecular basis for this unusual binding interaction. Of note, isolated N-terminal domains of the rat secretin and the VIP receptors are capable of high affinity binding of VIP. In the recently recognized secretin family of receptors, this domain has six conserved cysteine residues and disulfide bonds that are likely important to achieve the complex conformation critical for this binding. A single acidic residue (Asp98) present in the rat secretin receptor appears to be critical, because a site-mutant changing this to the polar, but uncharged residue present in that position in the human receptor (Asn) eliminates the high affinity binding of VIP. Of interest, a previously identified critical basic residue in VIP (Lys15) provides a candidate for charge-pairing with this residue, potentially aligning the peptide ligand in a nonproductive orientation within this receptor.     

A questionnaire study among 171 medical candidates enrolled in a PhD program. Three elements in the PhD education: supervision, research courses and international relations

One hundred and seventy-one medical doctors (median age 34 years) registered as Ph.D.-students at the Medical Faculty, University of Aarhus, were given a questionnaire concerning the Ph.D-program (91% reply rate). The Ph.D.-students had typically graduated four years before enrollment and had gained basic clinical experience. Eighty-four percent had been involved in research projects prior to their formal research education. In general, the Ph.D.-students found the supervision offered by senior researchers adequate, although, more Ph.D.-students in clinical than in preclinical departments would have liked their main supervisor to be more enthusiastic and have more specific expertise. By tradition, the Medical Faculty in Aarhus offers a broad introductory course on research methodology, this was appreciated by the Ph.D.-students. However, they found that too much time was allocated for this purpose. The Ministry of Education recommends that Ph.D.-students gain experience from international collaboration, preferably from a stay abroad. However, only 24% of Ph.D.-students had stayed at an international collaborating institution. Although the overall evaluation of the medical Ph.d.-program was positive, the Ph.D.-students pointed out weaknesses and conflicts requiring adjustment.     

A novel k-space trajectory measurement technique

OBJECTIVE: To report our experience with erosion of permanent suture or mesh material after abdominal sacrocolpopexy. METHODS: A retrospective chart review was performed to identify patients who underwent sacrocolpopexy by the same surgeon over 8 years. Demographic data, operative notes, hospital records, and office charts were reviewed after sacrocolpopexy. Patients with erosion of either suture or mesh were treated initially with conservative therapy followed by surgical intervention as required. RESULTS: Fifty-seven patients underwent sacrocolpopexy using synthetic mesh during the study period. The mean (range) postoperative follow-up was 19.9 (1.3-50) months. Seven patients (12%) had erosions after abdominal sacrocolpopexy with two suture erosions and five mesh erosions. Patients with suture erosion were asymptomatic compared with patients with mesh erosion, who presented with vaginal bleeding or discharge. The mean (+/-standard deviation) time to erosion was 14.0+/-7.7 (range 4-24) months. Both patients with suture erosion were treated conservatively with estrogen cream. All five patients with mesh erosion required transvaginal removal of the mesh. CONCLUSION: Mesh erosion can follow abdominal sacrocolpopexy over a long time, and usually presents as vaginal bleeding or discharge. Although patients with suture erosion can be managed successfully with conservative treatment, patients with mesh erosion require surgical intervention. Transvaginal removal of the mesh with vaginal advancement appears to be an effective treatment in patients failing conservative management.     

Investigation of the presynaptic effects of quinine and quinidine on the release and uptake of monoamines in rat brain tissue

Quinine and quinidine are reported to potentiate the behavioural effects of serotonergic agents and monoamine uptake inhibitors. We have therefore investigated the presynaptic actions of quinine and quinidine on monoamine uptake and release in rat brain tissue in vitro. Quinidine evoked the release of [3H]5-HT, [3H]noradrenaline and [3H]dopamine from pre-loaded rat brain slices in a concentration dependent manner with EC50 values of 175, 486 and 150 microM, respectively. Quinine induced [3H]monoamine release with similar potencies. Both quinine and quinidine also inhibited the active uptake of [3H]5-HT, [3H]noradrenaline and [3H]dopamine into rat brain synaptosomes with IC50 values in the range 0.13-12.4 microM. The potency of each drug to inhibit [3H]5-HT uptake was significantly higher than that for [3H]noradrenaline or [3H]dopamine. The relative potency of quinidine compared to quinine was more marked in the case of [3H]5-HT (58-fold) than for [3H]noradrenaline (3-fold) or [3H]dopamine (4-fold). The inhibition of [3H]5-HT uptake by quinine and quinidine was competitive in nature and corresponded with the potencies of these drugs to inhibit [3H]paroxetine binding. No correlation was observed between the potencies of quinine and quinidine to induce the release of [3H]monoamines and to inhibit their uptake, suggesting that these effects are mediated by two distinct mechanisms. We conclude that the presynaptic actions of quinine and quinidine on monoamine uptake and release may be implicated in their potentiation of the effects of serotonergic agents and uptake blockers.     

Comparative evaluation of FUNGITEST and broth microdilution methods for antifungal drug susceptibility testing of Candida species and Cryptococcus neoformans

The FUNGITEST method (Sanofi Diagnostics Pasteur, Paris, France) is a microplate-based procedure for the breakpoint testing of six antifungal agents (amphotericin B, flucytosine, fluconazole, itraconazole, ketoconazole, and miconazole). We compared the FUNGITEST method with a broth microdilution test, performed according to National Committee for Clinical Laboratory Standards document M27-A guidelines, for determining the in vitro susceptibilities of 180 isolates of Candida spp. (50 C. albicans, 50 C. glabrata, 10 C. kefyr, 20 C. krusei, 10 C. lusitaniae, 20 C. parapsilosis, and 20 C. tropicalis isolates) and 20 isolates of Cryptococcus neoformans. Overall, there was 100% agreement between the methods for amphotericin B, 95% agreement for flucytosine, 84% agreement for miconazole, 83% agreement for itraconazole, 77% agreement for ketoconazole, and 76% agreement for fluconazole. The overall agreement between the methods exceeded 80% for all species tested with the exception of C. glabrata (71% agreement). The poorest agreement between the results for individual agents was seen with C. glabrata (38% for fluconazole, 44% for ketoconazole, and 56% for itraconazole) and C. tropicalis (50% for miconazole). The FUNGITEST method misclassified as susceptible 2 of 12 (16.6%) fluconazole-resistant isolates, 2 of 10 (20%) itraconazole-resistant isolates, and 4 of 8 (50%) ketoconazole-resistant isolates of several Candida spp. Further development of the FUNGITEST procedure will be required before it can be recommended as an alternative method for the susceptibility testing of Candida spp. or C. neoformans.     

Just a matter of time

As Midwestern foodservice directors & dietitians recently discovered when an earthquake alert was sounded in their area, it's never too early to review & update emergency plans. Herein is a compendium of tips that can be used by any foodservice professional working in an area at risk of disaster, whether it be earthquake, tornado, hurricane, blackout or flood.