Interactions Among Positions in the Third and Fourth Membrane-Associated Domains at the Intersubunit Interface of the N-Methyl-D-Aspartate Receptor Forming Sites of Alcohol Action

The N-methyl-d-aspartate (NMDA) glutamate receptor is a major target of ethanol in the brain. Previous studies have identified positions in the third and fourth membrane-associated (M) domains of the NMDA receptor GluN1 and GluN2A subunits that influence alcohol sensitivity. The predicted structure of the NMDA receptor, based on that of the related GluA2 subunit, indicates a close apposition of the alcohol-sensitive positions in M3 and M4 between the two subunit types. We tested the hypothesis that these positions interact to regulate receptor kinetics and ethanol sensitivity by using dual substitution mutants. In single-substitution mutants, we found that a position in both subunits adjacent to one previously identified, GluN1(Gly-638) and GluN2A(Phe-636), can strongly regulate ethanol sensitivity. Significant interactions affecting ethanol inhibition and receptor deactivation were observed at four pairs of positions in GluN1/GluN2A: Gly-638/Met-823, Phe-639/Leu-824, Met-818/Phe-636, and Leu-819/Phe-637; the latter pair also interacted with respect to desensitization. Two interactions involved a position in M4 of both subunits, GluN1(Met-818) and GluN2A(Leu-824), that does not by itself alter ethanol sensitivity, whereas a previously identified ethanol-sensitive position, GluN2A(Ala-825), did not unequivocally interact with any other position tested. These results also indicate a shift by one position of the predicted alignment of the GluN1 M4 domain. These findings have allowed for the refinement of the NMDA receptor M domain structure, demonstrate that this region can influence apparent agonist affinity, and support the existence of four sites of alcohol action on the NMDA receptor, each consisting of five amino acids at the M3-M4 domain intersubunit interfaces

Isostaticity and the solidification of semiflexible polymer melts

Using molecular dynamics simulations of a tangent-soft-sphere bead-spring polymer model, we examine the degree to which semiflexible polymer melts solidify at isostaticity. Flexible and stiff chains crystallize when they are isostatic as defined by appropriate degree-of-freedom-counting arguments. Semiflexible chains also solidify when isostatic if a generalized isostaticity criterion that accounts for the slow freezing out of configurational freedom as chain stiffness increases is employed. The dependence of the average coordination number at solidification $Z(T_s)$ on chains' characteristic ratio $C_\infty$ has the same functional form [$Z \simeq a - b\ln(C_\infty)$] as the dependence of the average coordination number at jamming $Z(\phi_J)$ on $C_\infty$ in athermal systems, suggesting that jamming-related phenomena play a significant role in thermal polymer solidification

Two Adjacent Phenylalanines In the NMDA Receptor GluN2A Subunit M3 Domain Interactively Regulate Alcohol Sensitivity and Ion Channel Gating

The N-methyl-d-aspartate (NMDA) receptor is a key target of ethanol action in the central nervous system. Alcohol inhibition of NMDA receptor function involves small clusters of residues in the third and fourth membrane-associated (M) domains. Previous results from this laboratory have shown that two adjacent positions in the M3 domain, F636 and F637, can powerfully regulate alcohol sensitivity and ion channel gating. In this study, we report that these positions interact with one another in the regulation of both NMDA receptor gating and alcohol action. Using dual mutant cycle analysis, we detected interactions among various substitution mutants at these positions with respect to regulation of glutamate EC50, steady-state to peak current ratios (Iss:Ip), mean open time, and ethanol IC50. This interaction apparently involves a balancing of forces on the M3 helix, such that the disruption of function due to a substitution at one position can be reversed by a similar substitution at the other position. For example, tryptophan substitution at F636 or F637 increased or decreased channel mean open time, respectively, but tryptophan substitution at both positions did not alter open time. Interestingly, the effects of a number of mutations on receptor kinetics and ethanol sensitivity appeared to depend upon subtle structural differences, such as those between the isomeric amino acids leucine and isoleucine, as they could not be explained on the basis of sidechain molecular volume or hydrophilicity

A Theoretical Investigation of the Stability of HPC

Several ab initio methods are applied to the study of two linear isomers of methylidyne phosphine, HCP, and HPC. Single-reference correlation methods ranging from second-order Møller-Plesset theory to coupled cluster singles and doubles theory with noninterative inclusion of connected triple excitations were applied in a variety of basis sets of increasing size. In addition, complete active space self-consistent field wave functions, multireference singles and doubles configuration interaction, and averaged coupled pair functional theory were also applied to HPC. For HPC comparison of the single-reference based results is made with experimental data and previous theory to assess the accuracy of the methods employed. The same single-reference-bsed methods are then applied to linear HPC in order to assess whether it is a stable minimum or a transition state (imaginary frequencies in two dimensions). It is found that linear HPC is not a minimum on the ground-state potential surface. However, relatively high levels of correlation must be used when single-reference-based methods are employed to arrive at this conclusion. The multireference-based methods are then applied to HPC, and they too predict that it is not a minimum on the ground electronic potential surface. The qualitative nature of linear HPC is examined using CASSCF and CCSD wave functions

Functional Interactions of Alcohol-sensitive Sites in the \u3cem\u3eN\u3c/em\u3e-Methyl-d-aspartate Receptor M3 and M4 Domains

The N-methyl-d-aspartate receptor is an important mediator of the behavioral effects of ethanol in the central nervous system. Previous studies have demonstrated sites in the third and fourth membrane-associated (M) domains of the N-methyl-d-aspartate receptor NR2A subunit that influence alcohol sensitivity and ion channel gating. We investigated whether two of these sites, Phe-637 in M3 and Met-823 in M4, interactively regulate the ethanol sensitivity of the receptor by testing dual substitution mutants at these positions. A majority of the mutations decreased steady-state glutamate EC50 values and maximal steady-state to peak current ratios (Iss/Ip), whereas only two mutations altered peak glutamate EC50 values. Steady-state glutamate EC50 values were correlated with maximal glutamate Iss/Ip values, suggesting that changes in glutamate potency were attributable to changes in desensitization. In addition, there was a significant interaction between the substituents at positions 637 and 823 with respect to glutamate potency and desensitization. IC50 values for ethanol among the mutants varied over the approximate range 100–325 mm. The sites in M3 and M4 significantly interacted in regulating ethanol sensitivity, although this was apparently dependent upon the presence of methionine in position 823. Molecular dynamics simulations of the NR2A subunit revealed possible binding sites for ethanol near both positions in the M domains. Consistent with this finding, the sum of the molecular volumes of the substituents at the two positions was not correlated with ethanol IC50 values. Thus, there is a functional interaction between Phe-637 and Met-823 with respect to glutamate potency, desensitization, and ethanol sensitivity, but the two positions do not appear to form a unitary site of alcohol action

Migration of Co in nickel oxide/hydroxide of a nickel electrode in a Ni/H2 cell

Cobalt redistribution in nickel active material has been reported. This redistribution was suspected to be related to capacity fading. The objective of this work is to establish a relationship between cobalt redistribution and capacity fading. Microscopic cobalt distribution in nickel active material was studied using three EDX techniques: line scan, point-by-point analysis, and dot maps. Results from this study are presented

SME adaptive capacity in response to environmental requirements: understanding it as a complex adaptive system

The pressure on Small and Medium sized Enterprises (SMEs) in emerging economies to adapt their production and management to meet global industrial environmental standards is enormous. These pressures come from both the international supply chain and the government’s environmental legislation. Yet, an effective way to help SMEs adapt to these challenges in emerging economies is not reported. Little is available about environmental adaptation process at SMEs in developing countries. This paper attempts to address this gap in knowledge. It uses the theory of Complex Adaptive Systems to understand the complex nature of environmental adaptation at SMEs, and more importantly, it outlines an agenda for further research to identify key success factors for the environmental adaptation process at SMEs based on the key components of such a system

Sentinel surveillance of HIV-1 transmitted drug resistance, acute infection and recent infection.

BackgroundHIV-1 acute infection, recent infection and transmitted drug resistance screening was integrated into voluntary HIV counseling and testing (VCT) services to enhance the existing surveillance program in San Francisco. This study describes newly-diagnosed HIV cases and characterizes correlates associated with infection.Methodology/principal findingsA consecutive sample of persons presenting for HIV VCT at the municipal sexually transmitted infections (STI) clinic from 2004 to 2006 (N = 9,868) were evaluated by standard enzyme-linked immunoassays (EIA). HIV antibody-positive specimens were characterized as recent infections using a less-sensitive EIA. HIV-RNA pooled testing was performed on HIV antibody-negative specimens to identify acute infections. HIV antibody-positive and acute infection specimens were evaluated for drug resistance by sequence analysis. Multivariable logistic regression was performed to evaluate associations. The 380 newly-diagnosed HIV cases included 29 acute infections, 128 recent infections, and 47 drug-resistant cases, with no significant increases or decreases in prevalence over the three years studied. HIV-1 transmitted drug resistance prevalence was 11.0% in 2004, 13.4% in 2005 and 14.9% in 2006 (p = 0.36). Resistance to non-nucleoside reverse transcriptase inhibitors (NNRTI) was the most common pattern detected, present in 28 cases of resistance (59.6%). Among MSM, recent infection was associated with amphetamine use (AOR = 2.67; p<0.001), unprotected anal intercourse (AOR = 2.27; p<0.001), sex with a known HIV-infected partner (AOR = 1.64; p = 0.02), and history of gonorrhea (AOR = 1.62; p = 0.03).ConclusionsNew HIV diagnoses, recent infections, acute infections and transmitted drug resistance prevalence remained stable between 2004 and 2006. Resistance to NNRTI comprised more than half of the drug-resistant cases, a worrisome finding given its role as the backbone of first-line antiretroviral therapy in San Francisco as well as worldwide. The integration of HIV-1 drug resistance, recent infection, and acute infection testing should be considered for existing HIV/STI surveillance and prevention activities, particularly in an era of enhanced efforts for early diagnosis and treatment