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Equivalent Position (equivalent + position)

Distribution by Scientific Domains

Chemistry	62%

Selected Abstracts

An Examination of the Role of HRD in Voluntary Turnover in Public Service Organizations

PERFORMANCE IMPROVEMENT QUARTERLY, Issue 4 2002
Kenneth R. Bartlett
ABSTRACT In this study I examine the role of HRD, job satisfaction, and organizational commitment in voluntary turnover decisions. A sample of managers from public service agencies who voluntarily left their job in the previous year is compared to a sample of currently employed managers in the same or equivalent position. Both quantitative and qualitative methods are used to determine if attitudes towards HRD were a factor in the turnover decision for those who voluntarily left and if it would be a factor in influencing turnover intentions in those currently employed in comparable positions. The level of job satisfaction and organizational commitment are also compared between the two groups of respondents. The implications of attitudes towards HRD and levels of job satisfaction and organizational commitment in the decision to turnover among public service managers are examined along with recommendations for further research on the role of HRD in turnover decisions. [source]

Structures of S. aureus thymidylate kinase reveal an atypical active site configuration and an intermediate conformational state upon substrate binding

PROTEIN SCIENCE, Issue 4 2006
Masayo Kotaka
Abstract Methicillin-resistant Staphylococcus aureus (MRSA) poses a major threat to human health, particularly through hospital acquired infection. The spread of MRSA means that novel targets are required to develop potential inhibitors to combat infections caused by such drug-resistant bacteria. Thymidylate kinase (TMK) is attractive as an antibacterial target as it is essential for providing components for DNA synthesis. Here, we report crystal structures of unliganded and thymidylate-bound forms of S. aureus thymidylate kinase (SaTMK). His-tagged and untagged SaTMK crystallize with differing lattice packing and show variations in conformational states for unliganded and thymidylate (TMP) bound forms. In addition to open and closed forms of SaTMK, an intermediate conformation in TMP binding is observed, in which the site is partially closed. Analysis of these structures indicates a sequence of events upon TMP binding, with helix ,3 shifting position initially, followed by movement of ,2 to close the substrate site. In addition, we observe significant conformational differences in the TMP-binding site in SaTMK as compared to available TMK structures from other bacterial species, Escherichia coli and Mycobacterium tuberculosis as well as human TMK. In SaTMK, Arg 48 is situated at the base of the TMP-binding site, close to the thymine ring, whereas a cis -proline occupies the equivalent position in other TMKs. The observed TMK structural differences mean that design of compounds highly specific for the S. aureus enzyme looks possible; such inhibitors could minimize the transfer of drug resistance between different bacterial species. [source]

A conserved cysteine residue in the third transmembrane domain is essential for homomeric 5-HT3 receptor function

THE JOURNAL OF PHYSIOLOGY, Issue 4 2010
Dai-Fei Wu
The cysteine (Cys) residue at position 312 in the third transmembrane domain (M3) is conserved among 5-hydroxytryptamine type 3 (5-HT3) receptor subunits and many other subunits of the nicotinic acetylcholine (nACh) related Cys-loop receptor family, including most of the ,-aminobutyric acid type A (GABAA) and glycine receptor subunits. To elucidate a possible role for the Cys-312 in human 5-HT3A receptors, we replaced it with alanine and expressed the 5-HT3A(C312A) mutant in HEK293 cells. The mutation resulted in an absence of 5-HT-induced whole-cell current without reducing homopentamer formation, surface expression or 5-HT binding. The 5-HT3A(C312A) mutant, when co-expressed with the wild-type 5-HT3A subunit, did not affect functional expression of receptors, suggesting that the mutant is not dominant negative. Interestingly, co-expression of 5-HT3A(C312A) with 5-HT3B led to surface expression of heteropentamers that mediated small 5-HT responses. This suggests that the Cys-312 is essential for homomeric but not heteromeric receptor gating. To further investigate the relationship between residue 312 and gating we replaced it with amino acids located at the equivalent position within other Cys-loop subunits that are either capable or incapable of forming functional homopentamers. Replacement of 5-HT3A Cys-312 by Gly or Leu (equivalent residues in the nACh receptor , and , subunits) abolished and severely attenuated function, respectively, whereas replacement by Thr or Ser (equivalent residues in nACh receptor ,7 and GABAA, subunits) supported robust function. Thus, 5-HT3A residue 312 and equivalent polar residues in the M3 of other Cys-loop subunits are essential determinants of homopentameric gating. [source]

Molecular cloning, genomic structure, and genetic mapping of two Rdl -orthologous genes of GABA receptors in the diamondback moth, Plutella xylostella

ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY (ELECTRONIC), Issue 2 2010
Guorui Yuan
Abstract The Resistance to dieldrin (Rdl) gene encodes a subunit of the insect , -aminobutyric acid (GABA) receptor. Cyclodiene resistance in many insects is associated with replacement of a single amino acid (alanine at position 302) with either a serine or a glycine in the Rdl gene. Two Rdl -orthologous genes of GABA receptors (PxGABAR,1 and PxGABAR,2) were cloned and sequenced from a susceptible strain (Roth) of Plutella xylostella. PxGABAR,1 and PxGABAR,2 showed 84% and 77% identity with the Rdl gene of Drosophila melanogaster at an amino acid level, respectively. The coding regions of PxGABAR,1 and PxGABAR,2 both comprise ten exons, with two alternative RNA-splicing forms in exon 3 of both genes. At the orthologous position of alanine-302 in D. melanogaster Rdl, PxGABAR,1 has a conserved alanine at position 282. PxGABAR,2 has a serine instead of an alanine at the equivalent position. With two informative DNA markers, both PxGABAR,1 and PxGABAR,2 were mapped onto the Z chromosome of P. xylostella. © 2010 Wiley Periodicals, Inc. [source]

Differential tetraethylammonium sensitivity of KCNQ1,4 potassium channels

BRITISH JOURNAL OF PHARMACOLOGY, Issue 3 2000
J K Hadley
In Shaker -group potassium channels the presence of a tyrosine residue, just downstream of the pore signature sequence GYG, determines sensitivity to tetraethylammonium (TEA). The KCNQ family of channels has a variety of amino acid residues in the equivalent position. We studied the effect of TEA on currents generated by KCNQ homomers and heteromers expressed in CHO cells. We used wild-type KCNQ1,4 channels and heteromeric KCNQ2/3 channels incorporating either wild-type KCNQ3 subunits or a mutated KCNQ3 in which tyrosine replaced threonine at position 323 (mutant T323Y). IC50 values were (mM): KCNQ1, 5.0; KCNQ2, 0.3; KCNQ3, >30; KCNQ4, 3.0; KCNQ2+KCNQ3, 3.8; and KCNQ2+KCNQ3(T323Y), 0.5. While the high TEA sensitivity of KCNQ2 may be conferred by a tyrosine residue lacking in the other channels, the intermediate TEA sensitivity of KCNQ1 and KCNQ4 implies that other residues are also important in determining TEA block of the KCNQ channels. British Journal of Pharmacology (2000) 129, 413,415; doi:10.1038/sj.bjp.0703086 [source]

The pair-functional method.

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2001

The theory of the pair-functional ensemble is developed to provide estimates of the pairing forces from experimental X-ray intensities. The statistical mechanics of the grand ensemble leads to a diagram expansion for the forces, in terms of the direct correlation function of the fluid ensemble combined with a series of small higher-order corrections. A simpler treatment, based on a biased Gaussian probability distribution, gives approximate formulae, valid for reflections of any type in all space groups. The role of symmetry is analysed. The entropy of an asymmetrical ensemble can always be increased by averaging it over equivalent positions of the atoms in the true space group, with the result that the atoms naturally tend to adopt the highest symmetry compatible with the data. In a cell with different types of atom, the atoms experience a single force function but they interact with a strength proportional to the products of their scattering factors. Numerical estimates are given for typical cases. [source]

Order,disorder twinning model and stacking faults in ,-NTO

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006
Dieter Schwarzenbach
Crystals of the recently published [Bolotina, Kirschbaum & Pinkerton (2005). Acta Cryst. B61, 577,584] triclinic (P) structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (,-NTO) occur as fourfold twins. There are Z, = 4 independent molecules per asymmetric unit. We show that the structure contains layers with 2-periodic layer-group symmetry p21/b 1 (1). This symmetry is lost through the stacking of the layers, which is a possible explanation for Z, = 4. A layer can assume four different but equivalent positions with respect to its nearest neighbor. Twinning arises through stacking faults and is an instructive example of the application of order,disorder theory using local symmetry operations. The near-neighbor relations between molecules remain unchanged through all twin boundaries. The four structures with maximum degree of order, one of which is the observed one, and the family reflections common to all domains are identified. Rods of weak diffuse scattering confirm the stacking model. [source]

Natural Diversity to Guide Focused Directed Evolution

CHEMBIOCHEM, Issue 13 2010
Helge Jochens Dr.
Abstract Simultaneous multiple site-saturation mutagenesis was performed at four active-site positions of an esterase from Pseudomonas fluorescens to improve its ability to convert 3-phenylbutyric acid esters (3-PBA) in an enantioselective manner. Based on an appropriate codon choice derived from a structural alignment of 1751 sequences of ,/,-hydrolase fold enzymes, only those amino acids were considered for library creation that appeared frequently in structurally equivalent positions. Thus, the number of mutants to be screened could be substantially reduced while the number of functionally intact variants was increased. Whereas the wild-type esterase showed only marginal activity and poor enantioselectivity (Etrue=3.2) towards 3-PBA-ethyl ester, a significant number of hits with improved rates (up to 240-fold) and enantioselectivities (up to Etrue=80) were identified in these "smart" libraries. [source]