220 research outputs found
HIV-1 Integrase–DNA Interactions Investigated by Molecular Modelling
HIV-1 integrase is the viral enzyme responsible for the insertion of the viral DNA into the host cell chromosome. This process occurs through two distinct biochemical reactions: the 3′-processing of the viral DNA and the transesterification reaction. Because experimental structural information on the reaction intermediate is not available, several molecular models have been developed. Unfortunately, none of the models of the enzyme–substrate complex is fully consistent with the available molecular biological data. We have constructed a new theoretical model based on mutagenesis experiments and cross-linking data, using a relatively accurate computational setup. The structural features of the model along with its limitations are discussed here
Convergent dynamics in the protease enzymatic superfamily
Proteases regulate various aspects of the life cycle in all organisms by
cleaving specific peptide bonds. Their action is so central for biochemical
processes that at least 2% of any known genome encodes for proteolytic enzymes.
Here we show that selected proteases pairs, despite differences in oligomeric
state, catalytic residues and fold, share a common structural organization of
functionally relevant regions which are further shown to undergo similar
concerted movements. The structural and dynamical similarities found
pervasively across evolutionarily distant clans point to common mechanisms for
peptide hydrolysis.Comment: 13 pages, 6 figure
Propofol inhibits prokaryotic voltage-gated Na+ channels by promoting activation-coupled inactivation
Propofol is widely used in the clinic for the induction and maintenance of general anesthesia. As with most general anesthetics, however, our understanding of its mechanism of action remains incomplete. Local and general anesthetics largely inhibit voltage-gated Na+ channels (Navs) by inducing an apparent stabilization of the inactivated state, associated in some instances with pore block. To determine the biophysical and molecular basis of propofol action in Navs, we investigated NaChBac and NavMs, two prokaryotic Navs with distinct voltage dependencies and gating kinetics, by whole-cell patch clamp electrophysiology in the absence and presence of propofol at clinically relevant concentrations (2-10 μM). In both Navs, propofol induced a hyperpolarizing shift of the pre-pulse inactivation curve without any significant effects on recovery from inactivation at strongly hyperpolarized voltages, demonstrating that propofol does not stabilize the inactivated state. Moreover, there was no evidence of fast or slow pore block by propofol in a non-inactivating NaChBac mutant (T220A). Propofol also induced hyperpolarizing shifts of the conductance-voltage relationships with negligible effects on the time constants of deactivation at hyperpolarized voltages, indicating that propofol does not stabilize the open state. Instead, propofol decreases the time constants of macroscopic activation and inactivation. Adopting a kinetic scheme of Nav gating that assumes preferential closed-state recovery from inactivation, a 1.7-fold acceleration of the rate constant of activation and a 1.4-fold acceleration of the rate constant of inactivation were sufficient to reproduce experimental observations with computer simulations. In addition, molecular dynamics simulations and molecular docking suggest that propofol binding involves interactions with gating machinery in the S4-S5 linker and external pore regions. Our findings show that propofol is primarily a positive gating modulator of prokaryotic Navs, which ultimately inhibits the channels by promoting activation-coupled inactivation. © 2018 Yang et al
Nonequilibrium thermodynamics of DNA nanopore unzipping
Using theory and simulations, we carried out a first systematic
characterization of DNA unzipping via nanopore translocation. Starting from
partially unzipped states, we found three dynamical regimes depending on the
applied force, f: (i) heterogeneous DNA retraction and rezipping (f < 17pN),
(ii) normal (17pN 60pN) drift-diffusive
behavior. We show that the normal drift-diffusion regime can be effectively
modelled as a one-dimensional stochastic process in a tilted periodic
potential. We use the theory of stochastic processes to recover the potential
from nonequilibrium unzipping trajectories and show that it corresponds to the
free-energy landscape for single base-pairs unzipping. Applying this general
approach to other single-molecule systems with periodic potentials ought to
yield detailed free-energy landscapes from out-of-equilibrium trajectories.Comment: 6 pages, 4 figure
Assessment of trabecular bone score (TBS) in overweight/obese men: effect of metabolic and anthropometric factors
The "trabecular bone score" (TBS) indirectly explores bone quality, independently of bone mineral density (BMD). We investigated the effects of anthropometric and metabolic parameters on TBS in 87 overweight/obese men. We assessed BMD and TBS by DXA, and some parameters of glucose metabolism, sex-and calciotropic hormone levels. Regression models were adjusted for either age and BMI, or age and waist circumference, or age and waist/hip ratio, also considering BMI >35 (y/n) and metabolic syndrome (MS) (y/n). Correlations between TBS and parameters studied were higher when correcting for waist circumference, although not significant in subjects with BMI >35. The analysis of covariance showed that the same model always had a higher adjusted r-square index. BMD at lumbar spine and total hip, fasting glucose, bioavailable testosterone, and sex hormone-binding globulin are the only covariates having a significant effect (p 35 on TBS values or significant interaction terms between each covariate and either BMI >35 or the presence of MS. Obesity negatively affected TBS, despite unchanged BMD. Alterations of glucose homeostasis and sex hormone levels seem to influence this relationship, while calciotropic hormones have no role. The effect of waist circumference on TBS is more pronounced than that of BMI
Short-term effects of glucagon-like peptide 1 (GLP-1) receptor agonists on fat distribution in patients with type 2 diabetes mellitus: an ultrasonography study
AIMS:Glucagon-like peptide 1 receptor agonists (GLP-1 RA) induce weight loss and reduction in adipose tissue, but the effects of GLP-1 RA on the distribution of fat deposits have been poorly investigated.
METHODS: In 25 patients with type 2 diabetes (16 females and 9 males, mean age 63.5 ± 8.8 years), treated with GLP-1 RA (exenatide, n. 12; liraglutide, n.13), both before and 3 months after starting treatment, an abdominal ultrasonographic scan, with Doppler of renal arteries, and echocardiography were performed. Subcutaneous fat width (peri-umbilical and sub-xiphoid), deep fat deposits (pre-aortic, peri-renal, and epicardial), and renal resistive index (RI) were evaluated.
RESULTS: GLP-1 RA induced highly significant (p < 0.001) decrease in BMI and in fat thickness at all the assessed sites, without differences between exenatide and liraglutide treatment. A slight decrease in RI (p = 0.055) was also found. The percent changes of fat thickness was different between sites (p < 0.025), and the changes in subcutaneous deposits showed no significant correlation (p = 0.064) with those of deep fat deposits.
CONCLUSIONS: A short course of treatment with GLP-1 RA, besides weight loss, induces a redistribution of adipose tissue deposits, possibly contributing to a better cardiovascular risk profile in patients with type 2 diabetes mellitus
Mechanistic Insights into the Modulation of Voltage-Gated Ion Channels by Inhalational Anesthetics
AbstractGeneral anesthesia is a relatively safe medical procedure, which for nearly 170 years has allowed life saving surgical interventions in animals and people. However, the molecular mechanism of general anesthesia continues to be a matter of importance and debate. A favored hypothesis proposes that general anesthesia results from direct multisite interactions with multiple and diverse ion channels in the brain. Neurotransmitter-gated ion channels and two-pore K+ channels are key players in the mechanism of anesthesia; however, new studies have also implicated voltage-gated ion channels. Recent biophysical and structural studies of Na+ and K+ channels strongly suggest that halogenated inhalational general anesthetics interact with gates and pore regions of these ion channels to modulate function. Here, we review these studies and provide a perspective to stimulate further advances
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