Understanding ligand-based modulation of the Hsp90 molecular chaperone dynamics at atomic resolution

Molecular switching and ligand-based modulation of the 90-kDa heat-shock protein (Hsp90) chaperone activity may ultimately facilitate conformational coupling to the ATPase cycle along with activation and recruitment of the broad range of client proteins. We present an atomic resolution analysis of the Hsp90 N-terminal domain (NTD) binding energy landscape by simulating protein dynamics with a range of binding partners. We show that the activity of the molecular chaperone may be linked to (i) local folding-unfolding transitions and conformational switching of the "active site lid" upon binding and (ii) differences in the underlying protein dynamics as a function of the binding partner. This study suggests that structural plasticity of the Hsp90 NTD can be exploited by the molecular chaperone machinery to modulate enhanced structural rigidity during ATP binding and increased protein flexibility as a consequence of the inhibitor binding. The present study agrees with the experimental structural data and provides a plausible molecular model for understanding mechanisms of modulation of molecular chaperone activities by binding partners.     

NADH oxidase activity of rat cardiac sarcoplasmic reticulum regulates calcium-induced calcium release

NADH and Ca2+ have important regulatory functions in cardiomyocytes related to excitation-contraction coupling and ATP production. To elucidate elements of these functions, we examined the effect of NADH on sarcoplasmic reticulum (SR) Ca2+ release and the mechanisms of this regulation. Physiological concentrations of cytosolic NADH inhibited ryanodine receptor type 2 (RyR2)-mediated Ca2+-induced Ca2+ release (CICR) from SR membranes (IC50=120 micromol/L) and significantly lowered single channel open probability. In permeabilized single ventricular cardiomyocytes, NADH significantly inhibited the amplitude and frequency of spontaneous Ca2+ release. Blockers of electron transport prevented the inhibitory effect of NADH on CICR in isolated membranes and permeabilized cells, as well as on the activity of RyR2 channels reconstituted in lipid bilayer. An endogenous NADH oxidase activity from rat heart copurified with SR enriched with RyR2. A significant contribution by mitochondria was excluded as NADH oxidation by SR exhibited >9-fold higher catalytic activity (8.8 micromol/mg protein per minute) in the absence of exogenous mitochondrial complex I (ubiquinone) or complex III (cytochrome c) electron acceptors, but was inhibited by rotenone and pyridaben (IC50=2 to 3 nmol/L), antimycin A (IC50=13 nmol/L), and diphenyleneiodonium (IC50=28 micromol/L). Cardiac junctional SR treated with [3H](trifluoromethyl)diazirinyl-pyridaben specifically labeled a single 23-kDa PSST-like protein. These data indicate that NADH oxidation is tightly linked to, and essential for, negative regulation of the RyR2 complex and is a likely component of an important physiological negative-feedback mechanism coupling SR Ca2+ fluxes and mitochondrial energy production.     

Repair of Congenital Right Atrial Aneurysm Associated With Wolff-Parkinson-White Syndrome in a 5-Year-Old Girl

This report describes our experience with a 5-year-old girl who had an extremely rare presentation of a right atrial aneurysm and associated Wolff-Parkinson-White syndrome. Before being referred to our department, she underwent an ineffective radiofrequency ablation for repeated episodes of paroxysmal supraventricular tachycardia that were causing dizziness, palpitations, and chest discomfort. We resected the aneurysm with good results; she was doing well and was in normal sinus rhythm at the time of her 1-year follow-up visit.     

Vitreous hemorrhage in diabetic eyes previously treated with panretinal photocoagulation

Background Vitreous hemorrhage (VH) is a major cause of severe vision loss in diabetic patients. The aim of this study was to assess the incidence and risk factors for new VH in diabetics previously treated with panretinal photocoagulation (PRP) for proliferative retinopathy (PDR) in community base center. Methods Records of 192 diabetics (35 type 1, 157 type 2), undergoing PRP for diabetic retinopathy were retrospectively reviewed. Eyes presenting initially with high-risk PDR received PRP without delay, and eyes presenting initially with severe non proliferative retinopathy (NPDR) or early PDR had undergone central retinal photocoagulation (CRP), and then, when high risk PDR developed, received PRP treatment. Results VH had developed in 39% of the eyes despite PRP. Risk factors for VH in type 1 diabetes were: early onset and long duration of disease (23.8 versus 39.0 years of age, P = 0.007, and 25.8 versus 16.0 years, P = 0.002, respectively). In type 2, VH occurred with less follow-up and angiographic examinations (7.4% versus 3.8%, P = 0.027, and 33% versus 47%, P = 0.07, respectively). CRP decreased the risk for VH from 43 to 15%, P = 0.013. Conclusions In type 2 diabetes, regular ophthalmic follow-up and intensive PRP may reduce the risk for VH in eyes previously treated by PRP. In type 1, early onset disease and long duration are associated with higher incidence of VH.     

Correlation of prolactin concentration with levels of other hormones and with ultrastructural morphometric parameters of the testes in the human fetus

Consideration is given to the correlations between variations of the prolactin concentration and other hormonal parameters in the human embryonic period. The interrelation between the prolactin concentration and ultrastructural parameters of the testes is also traced. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 6, pp. 654–656, June, 1995 Presented by O. V. Volkova, Member of the Russian Academy of Medical Sciences     

A Method for Temporary Complete Substitution of Gas Exchange Function of the Lung

Total substitution of lung gas exchange function can be achieved by oxygenating all blood in a heart-lung machine and requires thoracotomy. In accordance with calculations based on physical principles, if extracorporeal oxygenation is combined with barometric pressure raised to 3 atm, half of the cardiac output will suffice to maintain normal blood oxygenation. Excessive amounts of oxygen dissolved in blood passed through an oxygenator will suffice for the total oxygenation of the rest of the blood. This assumption was investigated in 15 experiments on dogs and one human patient in a hyperbaric chamber. The bubble oxygenator and pneumatic membrane pumps were used. The results suggest that this method of total substitution of lung gas exchange function is feasible. This technique does not require thoracotomy and can be carried out on a patient in any position on the operating table. This method can be used during bronchoscopy treatment, lung lavage, and trachea surgery.     

Local effects of acute ethanol on dopamine neurotransmission in the ventral striatum in C57BL/6 mice

In this study, fast-scan cyclic voltammetry in brain slices was used to evaluate the effects of acute ethanol on dopamine terminal release and uptake in the nucleus accumbens of C57BL/6 mice. We found that pharmacologically relevant concentrations of ethanol (20 and 100 mM) did not alter electrically evoked dopamine release, while the highest concentration (200 mM) significantly decreased release (approximately 45%). No significant changes were observed in the rate of dopamine uptake after ethanol (20, 100 or 200 mM). In addition, it was established that a moderate dose (2 g/kg, i.p.) of ethanol did not alter the rate of dopamine synthesis, measured as L-dihydroxyphenylalanine (L-DOPA) accumulation. However, a high dose (5 g/kg, i.p.) of ethanol significantly increased the levels of L-DOPA to 60% above the control value. These data are consistent with earlier findings obtained in brain slices from rats; dopamine release, but not clearance, is affected by acute ethanol.