Elongation arrest by SecM via a cascade of ribosomal RNA rearrangements

In E. coli, the SecM nascent polypeptide causes elongation arrest, while interacting with 23S RNA bases A2058 and A749-753 in the exit tunnel of the large ribosomal subunit. We compared atomic models fitted by real-space refinement into cryo-electron microscopy reconstructions of a pretranslocational and SecM-stalled E. coli ribosome complex. A cascade of RNA rearrangements propagates from the exit tunnel throughout the large subunit, affecting intersubunit bridges and tRNA positions, which in turn reorient small subunit RNA elements. Elongation arrest could result from the inhibition of mRNA.(tRNAs) translocation, E site tRNA egress, and perhaps translation factor activation at the GTPase-associated center. Our study suggests that the specific secondary and tertiary arrangement of ribosomal RNA provides the basis for internal signal transduction within the ribosome. Thus, the ribosome may itself have the ability to regulate its progression through translation by modulating its structure and consequently its receptivity to activation by cofactors.     

Simulated dipeptide recognition by vancomycin

The antimicrobial activity of vancomycin and related glycopeptide antibiotics is due to stereospecific recognition of polypeptide components in bacterial cell walls. To better understand how these antibiotics recognize polypeptide determinants, we have developed dynamic models of the complexes formed by the vancomycin aglycon and two different dipeptide ligands, Ac-D-ala-D-ala and Ac-D-ala-gly. Molecular dynamics simulations of the two complexes, initially conditioned with distance constraints derived from two-dimensional nuclear magnetic resonance (NMR) studies, are conformationally stable and propagate in a manner consistent with the NMR-derived constraints after the constraints are removed. Free energy calculations accurately predict the relative binding affinity of these two complexes and help validate the simulation models for detailed structural analysis. Although the two ligands adopt similar conformations when bound to the antibiotic, there are clear differences in the configuration of intermolecular hydrogen bonds, the overall shape of the antibiotic, and other structural features of the two complexes. This analysis illustrates how complex structural and dynamic factors interrelate and contribute to differences in binding affinity. © 1997 John Wiley & Sons, Ltd.     

Opiate regulation of IL-1beta and TNF-alpha in cultured human articular chondrocytes

In order to investigate if beta-endorphins anti-inflammatory effect in cartilage-damaging states is mediated via tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), we examined its influence on these two cytokines in vitro. Human articular chondrocytes were obtained from patients undergoing total knee arthroplasty and stimulated with beta-endorphin (60-6000 ng/ml). Protein levels of TNF-alpha and IL-1 beta were measured by ELISA in supernatants from articular chondrocyte cultures. beta-Endorphin significantly increased the levels of IL-1 beta for all concentrations used after 15 min incubation, and when stimulated with 600 and 6000 ng/ml after 24 h incubation. The opioid-induced increase in IL-1 beta was blocked by naltrexone in the group tested. TNF-alpha expression was also significantly stimulated by 60 and 600 ng/ml beta-endorphin after 15 min, an effect blocked by naltrexone in the group tested. These findings indicate that the mechanism of beta-endorphins anti-inflammatory influence in cartilage-damaging states is not apparently mediated via these two cytokines modulation.     

Target intraocular pressure in the management of glaucoma

Achievement of target intraocular pressure is the goal of every efficient antiglaucoma therapy. Target intraocular pressure is the level of intraocular pressure which is associated with minimal likelihood of visual field or optic nerve lesion, or an existing lesion progression due to elevated intraocular pressure. Results of large clinical studies which have offered some new concepts on target intraocular pressure in the management of glaucoma are reviewed. An association between the curve of intraocular pressure decrease and glaucoma progression was demonstrated in these studies. Generally, a lower value of target intraocular pressure implies better protection from the loss of vision and visual field impairment in glaucoma patients. In advanced glaucoma, the greatest possible reduction from the initial intraocular pressure should be attempted. A 20% reduction from the initial intraocular pressure or decrease to < 18 mmHg in advanced glaucoma has been recognized as a favorable strategy to reach target intraocular pressure. In normal tension glaucoma, a lower value of target intraocular pressure is associated with a slower disease progression. In patients with initial glaucoma, 25% reduction from the initial intraocular pressure will slow down the disease progression by 45%. The value of target intraocular pressure depends on the pretreatment level of intraocular pressure, optic nerve condition, glaucoma disease state, rate of glaucoma progression, patient's age, and other risk factors for the development of glaucoma.     

Treatment of pseudophakic cystoid macular oedema

Cystoid oedema of macula is the most frequent problem following non-complicated cataract surgery, which leads to weakening of visual acutity. We have studied the treatment outcomes of the topical therapy with corticosteroids and nonsteroid antirheumatics during prospective randomized study in comparison with orally applied acethazolamide. However, 8 weeks later in treatment was observed a positive effect in both groups, on the eyes of patients, treated with acetazolamide, resorption of the oedema was faster, more intensive and ultimate visual acutity was statistically significantly better. Results demonstrated a benefit of combined therapy with antiinflamative drugs and orally prescribed acetazolamide in pseudophakic macular oedema.     

Ocular blood flow parameters in patients with rhegmatogenous retinal detachment

The aim of the present study is to evaluate the potential statistically significant differences in the ocular blood flow parameters in eyes with rhegmatogenous retinal detachment (RD). Eleven patients, 5 females and 6 males, mean age 46 years (range 22-70), with the unilateral rhegmatogenous RD were enrolled in the study. Colour Doppler Ultrasound was used to measure ocular blood flow velocities in the ophthalmic artery (OA), posterior ciliary's arteries (PCA) and ophthalmic vein (OV). The contralateral eye served as a control. All Doppler examinations were performed 1 day before and exactly 3 days after the retinal detachment surgery. The measurements of the peak systolic velocity (Vmax), diastolic velocity (Vd), minimum velocity (Vmin), time-averaged velocity (TAV), resistive index (RI) and pulsatility index (PI) showed no statistically significant difference (by paired Student's t-test, p > 0.05) between the OA, PCA and OV in healthy eyes and eyes with RD before operation, as well as between the eyes with RD before and after the operation. Only was increased RI in OV of eyes with RD after the surgery (p < 0.05). All these parameters were not related with 2 or more quadrants of RD, but the difference in duration of retinal detachment in days is statistically significant (by Wilcoxon t-test p > 0.05). Pearson correlation method gave statistically significant correlation between RI and PI of the OA in healthy eyes (r = 0.826, p < 0.01), eyes with RD before operation (r = 0.847, p < 0.01) and eyes with RD after the operation (r = 0.856, p < 0.01). Formula for the calculation of PI by RI was derived using linear regression analysis in all three cases. Scleral buckling surgery leaves the ocular blood parameters in OA unchanged. The correlation between RD and logarithm of duration of RD in days is statistically significant.     

Mechanistic study of the structure–activity relationship for the free radical scavenging activity of baicalein

Density functional theory calculations were performed to evaluate the antioxidant activity of baicalein. The conformational behaviors of both the isolated and the aqueous-solvated species (simulated with the conductor-like polarizable continuum solvation model) were analyzed at the M052X/6-311 + G(d,p) level. The most stable tautomers of various forms of baicalein displayed three IHBs between O4 and OH5, O5 and OH6, and O6 and OH7. The most stable tautomer of the baicalein radical was obtained by dehydrogenating the hydroxyl at C6, while the most stable anion tautomer was obtained by deprotonating the C7 hydroxyl in gaseous and aqueous phases. The expected antioxidant activity of baicalein was explained by its ionization potentials (IPs) and homolytic O–H bond dissociation enthalpies (BDEs), which were obtained via the UM052X optimization level of the corresponding radical species. Heterolytic O–H bond cleavages (proton dissociation enthalpies, PDEs) were also computed. The calculated IP, BDE, and PDE values suggested that one-step H-atom transfer, rather than sequential proton loss–electron transfer or electron transfer–proton transfer, would be the most favorable mechanism for explaining the antioxidant activity of baicalein in the gas phase and in nonpolar solvents. In aqueous solution, the SPLET mechanism was more important.     

Mutations in LAMB1 Cause Cobblestone Brain Malformation without Muscular or Ocular Abnormalities

Cobblestone brain malformation (COB) is a neuronal migration disorder characterized by protrusions of neurons beyond the first cortical layer at the pial surface of the brain. It is usually seen in association with dystroglycanopathy types of congenital muscular dystrophies (CMDs) and ocular abnormalities termed muscle-eye-brain disease. Here we report homozygous deleterious mutations in LAMB1, encoding laminin subunit beta-1, in two families with autosomal-recessive COB. Affected individuals displayed a constellation of brain malformations including cortical gyral and white-matter signal abnormalities, severe cerebellar dysplasia, brainstem hypoplasia, and occipital encephalocele, but they had less apparent ocular or muscular abnormalities than are typically observed in COB. LAMB1 is localized to the pial basement membrane, suggesting that defective connection between radial glial cells and the pial surface mediated by LAMB1 leads to this malformation.