Prefrontal-related functional connectivities within the default network are modulated by COMT val158met in healthy young adults

Previous studies have supported the concept that the default network is an intrinsic brain system that participates in internal modes of cognition. Neural activity and connectivity within the default network, which are correlated with cognitive ability even at rest, may be plausible intermediate phenotypes that will enable us to understand the genetic mechanisms of individuals' cognitive function or the risk for genetic brain diseases. Using resting functional magnetic resonance imaging and imaging genetic paradigms, we investigated whether individual default network connectivity was modulated by COMT val(158)met in 57 healthy young subjects. Compared with COMT heterozygous individuals, homozygous val individuals showed significantly decreased prefrontal-related connectivities, which primarily occurred between prefrontal regions and the posterior cingulate/restrosplenial cortices. Further analyses of the topological characteristics of the default network showed homozygous val individuals had significantly fewer node degrees in the prefrontal regions. This finding may partially elucidate previous reports that the COMT val variant is associated with inefficient prefrontal information processing and poor cognitive performance. Our findings suggest that default network connectivity that involves the prefrontal cortex is modulated by COMT val(158)met through differential effects on prefrontal dopamine levels.

Brain-derived neurotrophic factor val66met polymorphism affects prefrontal energy metabolism in bipolar disorder

Brain-derived neurotrophic factor val66met polymorphism has been implicated in the pathophysiology of bipolar disorder. We investigated the neurochemistry of the left dorsolateral prefrontal cortex of bipolar disorder and healthy participants in relation to the brain-derived neurotrophic factor val66met polymorphism using H-magnetic resonance spectroscopy. Absolute N-acetyl-aspartate, phosphocreatine+creatine (PCr+Cr), choline-containing compounds, myo-inositol, and glutamate levels were measured. Bipolar disorder met-carriers had lower PCr+Cr levels than bipolar disorder val/val patients, and bipolar disorder val/val patients had higher PCr+Cr levels than val/val healthy controls. These results indicate that bipolar disorder met-carriers have abnormal energy metabolism in the left dorsolateral prefrontal cortex.

COMT Val158Met and 5HTTLPR functional loci interact to predict persistence of anxiety across adolescence: results from the Victorian Adolescent Health Cohort Study

We investigated whether a composite genetic factor, based on the combined actions of catechol-O-methyltransferase (COMT) (Val(158)Met) and serotonin transporter (5HTTLPR) (Long-Short) functional loci, has a greater capacity to predict persistence of anxiety across adolescence than either locus in isolation. Analyses were performed on DNA collected from 962 young Australians participating in an eight-wave longitudinal study of mental health and well-being (Victorian Adolescent Health Cohort Study). When the effects of each locus were examined separately, small dose-response reductions in the odds of reporting persisting generalized (free-floating) anxiety across adolescence were observed for the COMT Met(158) [odds ratio (OR) = 0.85, 95% confidence interval (CI) = 0.76-0.95, P = 0.004] and 5HTTLPR Short alleles (OR = 0.88, CI = 0.79-0.99, P = 0.033). There was no evidence for a dose-response interaction effect between loci. However, there was a double-recessive interaction effect in which the odds of reporting persisting generalized anxiety were more than twofold reduced (OR = 0.45, CI = 0.29-0.70, P < 0.001) among carriers homozygous for both the COMT Met(158) and the 5HTTLPR Short alleles (Met(158)Met + Short-Short) compared with the remaining cohort. The double-recessive effect remained after multivariate adjustment for a range of psychosocial predictors of anxiety. Exploratory stratified analyses suggested that genetic protection may be more pronounced under conditions of high stress (insecure attachments and sexual abuse), although strata differences did not reach statistical significance. By describing the interaction between genetic loci, it may be possible to describe composite genetic factors that have a more substantial impact on psychosocial development than individual loci alone, and in doing so, enhance understanding of the contribution of constitutional processes in mental health outcomes.

Val326 of Thermoactinomyces vulgaris R-47 amylase II modulates the preference for alpha-(1,4)- and alpha-(1,6)-glycosidic linkages

Thermoactinomyces vulgaris R-47 alpha-amylase II (TVA II) catalyzes not only the hydrolysis of alpha-(1,4)- and alpha-(1,6)-glycosidic linkages but also transglycosylation. The subsite +1 structure of alpha-amylase family enzymes plays important roles in substrate specificity and transglycosylation activity. We focused on the amino acid residue at the 326th position based on information on the primary structure and crystal structure, and replaced Val with Ala, Ile, or Thr. The V326A mutant favored hydrolysis of the alpha-(1,4)-glycosidic linkage compared to the wild-type enzyme. In contrast, the V326I mutant favored hydrolysis of the alpha-(1,6)-glycosidic linkage and exhibited low transglycosylation activity. In the case of the V326T mutant, the hydrolytic activity was almost identical to that of the wild-type TVA II, and the transglycosylation activity was poor. These results suggest that the volume and the hydrophobicity of the amino acid residue at the 326th position modulate both the preference for glycosidic linkages and the transglycosylation activity.

Effect of von Willebrand Factor on the Pharmacokinetics of Recombinant Human Platelet Glycoprotein Ibα-Immunoglobulin G1 Chimeric Proteins

PURPOSE

Recombinant human platelet glycoprotein Ibalpha-immunoglobulin G1 chimeric proteins (GPIbalpha-Ig) have varying levels of anti-thrombotic activities based on their ability to compete for platelet mediated adhesion to von Willebrand Factor (vWF). Valine substituted GPIbalpha-Ig chimeras, at certain position, increase the binding affinity to vWF over its "wild-type" GPIbalpha-Ig analog. The purpose of this study was to determine the pharmacokinetics of two valine substituted GPIbalpha-Ig chimeras, GPIbalpha-Ig/1V (valine substitution at 239 position) and GPIbalpha-Ig/2V (double valine substitution at 233 and 239 position), in mice, rats and dogs.

METHODS

Head-to-head comparisons of pharmacokinetics of GPIbalpha-Ig/1V and GPIbalpha-Ig/2V were investigated in rats and dogs after intravenous administration. Since vWF precipitates in the serum but not in plasma preparation, the concentration-time profiles of GPIbalpha-Ig/2V in rats were examined from the same blood samples for determination of matrix effect. The disposition of GPIbalpha-Ig/2V was also compared in vWF-deficient versus wild-type mice.

RESULTS

For GPIbalpha-Ig/2V, the serum clearances were 2.62+/-0.27 ml/hr/kg in rats and 1.97+/-0.24 ml/hr/kg in dogs. The serum clearances of less potent GPIbalpha-Ig/1V were 1.08+/-0.08 and 0.97+/-0.19 ml/hr/kg in rats and dogs, respectively. In addition, the serum clearance of GPlbalpha-Ig/2V of 1.53 ml/hr/kg in vWF-deficient mice was lower than that in wild-type mice of 2.79 ml/hr/kg.

CONCLUSION

The difference in disposition for valine substituted forms of GPIbalpha-Ig in laboratory animals are likely affected by their enhanced binding affinity for circulating vWF.

Interaction of HIV-1 Gag with the clathrin-associated adaptor AP-2

The envelope glycoprotein (Env) of HIV-1 interacts with the clathrin-associated adaptor complex AP-2 during the late phase of the viral replication cycle. Upon its synthesis, Env, therefore, is retrieved from the cellular surface unless internalization is inhibited by viral Gag. Here we demonstrate that not only Env, but also HIV-1 Gag, specifically binds to AP-2. Gag-AP-2 association was found to depend on tyrosine residue 132 and valine residue 135 at the matrix-capsid junction in the Gag polyprotein. Results of a morphological analysis of viral egress from cells expressing dominant-negative AP-2 suggest an involvement of AP-2 in confining HIV-1 exit to distinct microdomains. Further, particle release from AP-2-mutant cells was enhanced compared to release from wild-type cells but the infectivity of virus released from these cells was moderately reduced. Together these data attribute a role to the AP-2 complex in the regulation of HIV-1 assembly/release.

Possible steps to the emergence of life: the [GADV]-protein world hypothesis

Based on the fact that RNA has not only a genetic function but also a catalytic function, the RNA world theory on the origin of life was first proposed about 20 years ago. The theory assumes that RNA was amplified by self-replication to increase RNA diversity on the primitive earth. Since then, the theory has been widely accepted as the most likely explanation for the emergence of life. In contrast, we reached another hypothesis, the [GADV]-protein world hypothesis, which is based on pseudo-replication of [GADV]-proteins. We reached this hypothesis during studies on the origins of genes and the genetic code, where [G], [A], [D], and [V] refer to Gly, Ala, Asp, and Val, respectively. In this review, possible steps to the emergence of life are discussed from the standpoint of the [GADV]-protein world hypothesis, comparing it in parallel with the RNA world theory. It is also shown that [GADV]-peptides, which were produced by repeated dry-heating cycles and by solid phase peptide synthesis, have catalytic activities, hydrolyzing peptide bonds in a natural protein, bovine serum albumin. These experimental results support the [GADV]-protein world hypothesis for the origin of life.

COMT Val108/158Met genotype affects the mu-opioid receptor system in the human brain: evidence from ligand-binding, G-protein activation and preproenkephalin mRNA expression

Recent data from [(11)C]carfentanil ligand-PET indicate that in the human brain, the availability of mu-opioid (MOP) receptor binding sites is affected by the Val(108/158)Met polymorphism of the catechol-O-methyltransferase (COMT) gene. This prompted us to validate the impact of COMT Val(108/158)Met on MOP receptors in human post-mortem brain. [(3)H]DAMGO receptor autoradiography was performed in frontal cortex, basal ganglia, thalamus and cerebellum (8 Met/Met, 6 Met/Val, 3 Val/Val). With respect to genotype, numbers of MOP binding sites in COMT Met(108/158) homozygous and Val(108/158)Met heterozygous cases were higher than in Val(108/158) homozygous. Differences were significant in the caudate nucleus (Val/Met vs. Val/Val), nucleus accumbens (Val/Met vs. Val/Val) and the mediodorsal nucleus of the thalamus (Met/Met vs. Val/Val). In the thalamus, this was corroborated by DAMGO-stimulated [(35)S]GTPgammaS autoradiography. Moreover, stepwise multiple regression taking into account various covariables allowed to confirm the COMT genotype as the most predictive factor in this structure. As a mechanism how COMT might exert its action on MOP receptors, it has been suggested that at least in striatopallidal circuits COMT Val(108/158)Met impacts on enkephalin, which is capable of reciprocally regulating MOP receptor expression. Thus, we assessed preproenkephalin mRNA by in situ hybridization. In the striatum, mRNA levels were significantly higher in COMT Met(108/158) homozygous cases indicating that MOP binding sites and enkephalin are regulated in parallel. Moreover, the transcript was not detectable in the thalamus. Thus, mechanisms other than an enkephalin-dependent receptor turnover must be responsible for COMT-related differences in MOP binding site availability in the human brain.

Novel activating and inactivating mutations in the integrin beta1 subunit A domain

The ligand-binding activity of integrins is regulated by shape changes that convert these receptors from a resting (or inactive) state to an active state. However, the precise conformational changes that take place in head region of integrins (the site of ligand binding) during activation are not well understood. The portion of the integrin beta subunit involved in ligand recognition contains a von Willebrand factor type A domain, which comprises a central beta-sheet surrounded by seven alpha helices (alpha1-alpha7). Using site-directed mutagenesis, we show here that point mutation of hydrophobic residues in the alpha1 and alpha7 helices (which would be predicted to increase the mobility of these helices) markedly increases the ligand-binding activity of both integrins alpha5beta1 and alpha4beta1. In contrast, mutation of a hydrophilic residue near the base of the alpha1 helix decreases activity and also suppresses exposure of activation epitopes on the underlying hybrid domain. Our results provide new evidence that shifts of the alpha1 and alpha7 helices are involved in activation of the A domain. Although these changes are grossly similar to those defined in the A domains found in some integrin alpha subunits, movement of the alpha1 helix appears to play a more prominent role in betaA domain activation.

Effect of valine 106 on structure-function relation of cytosolic human thymidine kinase

Information on the regulation and structure-function relation of enzymes involved in DNA precursor synthesis is pivotal, as defects in several of these enzymes have been found to cause depletion or deletion of mitochondrial DNA resulting in severe diseases. Here, the effect of amino acid 106 on the enzymatic properties of the cell-cycle-regulated human cytosolic thymidine kinase 1 (TK1) is investigated. On the basis of the previously observed profound differences between recombinant TK1 with Val106 (V106WT) and Met106 (V106M) in catalytic activity and oligomerization pattern, we designed and characterized nine mutants of amino acid 106 differing in size, conformation and polarity. According to their oligomerization pattern and thymidine kinetics, the TK1 mutants can be divided into two groups. Group I (V106A, V106I and V106T) behaves like V106WT, in that pre-assay exposure to ATP induces reversible transition from a dimer with low catalytic activity to a tetramer with high catalytic activity. Group II (V106G, V106H, V106K, V106L and V106Q) behaves like V106M in that they are permanently high activity tetramers, irrespective of ATP exposure. We conclude that size and conformation of amino acid 106 are more important than polarity for the catalytic activity and oligomerization of TK1. The role of amino acid 106 and the sequence surrounding it for dimer-tetramer transition was confirmed by cloning the putative interface fragment of human TK1 and investigating its oligomerization pattern.

Effects of flecainide and quinidine on Kv4.2 currents: voltage dependence and role of S6 valines

1. The effects of flecainide and quinidine were studied on wild-type Kv4.2 channels (Kv4.2WT), channels with deletion of the N-terminal domain (N-del) and channels with mutations in the valine residues located at positions 402 and 404 in the presence (V[402,404]I) or in the absence (N-del/V[402,404]I) of the N-terminus. 2. The experiments were performed at 37 degrees C on COS7 cells using the whole-cell configuration of the patch-clamp technique. 3. Flecainide and quinidine inhibited Kv4.2WT currents in a concentration-dependent manner (IC(50)=23.6+/-1.1 and 12.0+/-1.4 microMat +50 mV, respectively), similar to their potency for the rest of the constructs at the same voltage. In Kv4.2WT channels, flecainide- and quinidine-induced block increased as channel inactivation increased. In addition, the inhibition produced by quinidine, but not by flecainide, increased significantly at positive test potentials. Similar effects were observed in N-del channels. However, in V[402,404]I and N-del/V[402,404]I channels, the voltage dependence of block by both quinidine and flecainide was lost, without significant modifications in potency at +50 mV. 4. These results point to an important role for S6 valines at positions 402 and 404 in mediating voltage-dependent block by quinidine and flecainide.

A point mutation in the constant region of Ig lambda1 prevents normal B cell development due to defective BCR signaling

Surface expression of B cell antigen receptors (BCRs) containing Ig and Igalpha/Igbeta generates signals required to transit discrete developmental checkpoints. The mechanism by which BCR components collaborate to initiate signals is still unclear. The expression of Iglambda1 in SJL mice is 50-fold lower than in other strains. Here, we demonstrate by gene targeting that a point mutation, which changes a glycine to a valine in the lambda1 constant region, is responsible for this defect. In vitro experiments show that Ig receptors bearing this mutation, while expressed normally, are deficient in signaling. These findings reveal a direct involvement of the Ig light chain (IgL) in B cell signaling and development beyond the requirement of light chains for BCR assembly.

Val193 and Phe195 of the gamma 1 34.5 protein of herpes simplex virus 1 are required for viral resistance to interferon-alpha/beta

Herpes simplex viruses (HSV) are resistant to the antiviral action of interferon. However, the underlying mechanisms are not well understood. In this report, we show that unlike that of wild-type HSV-1, replication of the gamma 1 34.5 null mutants was significantly inhibited by exogenous interferon-alpha in cells devoid of interferon-alpha/beta genes. Using a series of gamma 1 34.5 deletion mutants, the domain required for interferon resistance was mapped to the region containing amino acids 146 to 263 in the gamma 1 34.5 protein. Interestingly, Val193 Glu and Phe195 Leu substitutions in the protein phosphatase 1 interacting motif of the gamma 1 34.5 protein rendered HSV-1 sensitive to interferon-alpha. Furthermore, gamma 1 34.5 null mutants were sensitive to interferon-alpha/beta in PKR+/+ but not in PKR-/- mouse embryo fibroblasts. These findings provide evidence that the gamma 1 34.5 protein contributes to HSV-1 resistance to interferon-alpha/beta by inhibiting PKR function.

Purification of anthrax edema factor from Escherichia coli and identification of residues required for binding to anthrax protective antigen

The structural gene for anthrax edema factor (EF) was expressed in Escherichia coli under the control of a powerful T5 promoter to yield the 89-kDa recombinant protein that reacted with anti-EF antibodies. Recombinant EF was purified to homogeneity by a two-step procedure involving metal chelate affinity chromatography and cation-exchange chromatography. From 1 liter of culture, 2.5 mg of biologically active EF was easily purified. This is the first report of purification of anthrax EF from E. coli. EF purified from E. coli was biologically and functionally as active as its Bacillus anthracis counterpart. The recombinant protein could compete with lethal factor for binding to protective antigen. Sequence analysis revealed a stretch of seven amino acids, Val Tyr Tyr Glu Ile Gly Lys, present both in EF (residues 136 to 142) and lethal factor (residues 147 to 153). To investigate the role of these seven residues in binding to protective antigen, the residues were individually mutated to alanine in EF. Mutations in residues Tyr137, Tyr138, Ile140, and Lys142 of EF specifically blocked its interaction with anthrax protective antigen. The adenylate cyclase activity of the mutants remained unaffected. The results suggested that residues Tyr137, Tyr138, Ile140, and Lys142 are required for binding of EF to anthrax protective antigen, which facilitates its entry into susceptible cells.

Valine requirement of nursery pigs

Six experiments were conducted to determine the true digestible valine requirement of 5- to 20-kg pigs. In Exp. 1, a valine-deficient diet for 5- to 10-kg pigs was developed and validated in terms of growth performance in response to supplemental L-valine. A different basal diet was validated for 10- to 20-kg pigs in Exp. 2. Both diets were demonstrated to be deficient in valine and to support performance equivalent to typical nursery diets when fortified with L-valine. In Exp. 3, true ileal digestibility of valine in the two basal diets was determined in eight pigs fitted with a simple T-cannula at the terminal ileum. Another four pigs received an enzymatically hydrolyzed casein-based diet to determine endogenous contributions to collected ileal digesta. The two diets were found to have true valine digestibilities of 82% (5- to 10-kg pigs) and 86% (10- to 20-kg pigs). In Exp. 4, 80 weaned pigs (5.8 kg) were offered the basal diet fortified with five incremental doses (0.08%) of L-valine. Weight gain increased quadratically (P < 0.05) with increasing levels of valine. Broken-line analysis revealed a true digestible valine requirement of 0.86 +/- 0.03%. In Exp. 5, the true digestible valine requirement of 10- to 20-kg pigs was estimated with 120 pigs (10.9 kg) using the second basal diet fortified with six incremental doses (0.05%) of L-valine. The data suggested a digestible valine requirement level of about 0.775%, which was reevaluated in Exp. 6, wherein pigs did not respond to levels of digestible valine higher than 0.775%. In conclusion, requirement estimates were 2.50 and 2.22 g of true digestible valine per megacalorie of ME for 5- to 10- and 10- to 20-kg pigs, respectively. These empirical estimates are in close agreement with recent estimates of the National Research Council Subcommittee on Swine Nutrition of 2.48 and 2.11 g of true digestible valine per megacalorie of ME, respectively.

Influence of antioxidants and the CYP1A1 isoleucine to valine polymorphism on the smoking--lung cancer association

To evaluate the association between CYP1A1 genotype and lung cancer risk and to assess the effect of CYP1A1 genotype and antioxidant supplementation on the smoking--lung cancer relationship we conducted a case-control study nested within a large cancer prevention trial cohort. Controls (n = 324) were matched to cases (n = 282) on age (+/- 5 years), intervention group and study clinic in a 1:1 ratio, using incidence density sampling. Genotype was determined by a PCR-based method and logistic regression was used to calculate relative risk estimates. Overall, we found no association between CYP1A1 genotype and lung cancer risk. CYP1A1 genotype did not modify the effect of smoking on lung cancer risk. However, in an examination of subgroups defined by randomized intervention assignment our findings suggest that alpha-tocopherol supplementation may reduce the risk of lung cancer associated with cumulative smoking exposure regardless of CYP1A1 genotype with the greatest effect seen among those with the variant CYP1A1 allele.

Effects of dietary valine concentration on lactational performance of sows nursing large litters. NCR-42 Committe on Swine Nutrition

A cooperative study, using 231 primiand multiparous crossbred sows from six experiment stations (IN, KS, MI, MN, ND, and OH), was conducted to determine the effects of elevating dietary valine concentration in corn-soybean meal diets on lactational performance of sows nursing large litters. Crossbred sows were fed diets containing a minimum of .60% lysine during gestation. Sows were allotted at farrowing to four dietary valine concentrations, .80, .95, 1.10, and 1.25%. Crystalline L-valine replaced cornstarch to maintain a constant ratio of corn:soybean meal across diets. Dietary lysine, provided by corn, soybean meal, and .15% crystalline L-lysine x HCl, was .90% in all diets. Sows were allowed ad libitum access to feed. Sows were weighed within 24 h after farrowing, and all litters were adjusted to > or = 10 pigs/litter by d 2 following farrowing. Average sow parity, number of pigs on d 2, and lactation length for the four treatments were, respectively, 2.3, 2.3, 2.3, 2.5; 10.9, 10.8, 10.8, 10.7; and 25.1, 24.5, 25.2, 25.0 d. The ADFI during lactation was 5.87, 5.77, 5.87, and 5.74 kg (P > .50); hence, valine intakes were 41, 48, 55, and 61 g/d (linear, P < .01). Lysine intake ranged from 51.5 to 52.7 g/d (P > .50). Sow weight after farrowing averaged 198 kg (P > .60). Overall pig survival to weaning was high (>92%), and the number of pigs weaned (10.1, 10.3, 10.3, 10.3) did not differ (P > .30) among treatments. Litter weaning weights (73.6, 73.6, 74.5, 72.6 kg), litter weight gains (55.1, 55.1, 56.0, 54.1 kg), sow weight change during lactation (-4.9, -5.4, -4.8, -6.3 kg), and return-to-estrus interval (7.5, 6.4, 6.9, 8.2 d) were not affected (P > .30) by dietary valine. There were no station x treatment interactions (P > .50). These results indicate no benefit of elevated dietary valine for lactating sows nursing > or = 10 pigs and consuming a corn-soybean meal diet containing .90% lysine and .80% valine.

Enantioselectivity of bunitrolol 4-hydroxylation is reversed by the change of an amino acid residue from valine to methionine at position 374 of cytochrome P450-2D6

The enantioselectivity of 4-hydroxylation of bunitrolol (BTL), a beta-adrenoceptor blocking drug, was studied in microsomes from human liver, human hepatoma (Hep G2) cells expressing CYP2D6, and lymphoblastoid cells expressing CYP2D6. Kinetics in human liver microsomes showed that the Vmax value for (+)-BTL was 2.1-fold that of (-)-BTL, and that the Km value for (+)-BTL was lower than that for the (-)-antipode, resulting in the intrinsic clearance (Vmax/Km) of (+)-BTL being 2.1-fold over its (-)-antipode. CYP2D6 (CYP2D6-met) expressed in Hep G2 cells had a methionine residue at position 373 of the amino acid sequence and a rat-type N-terminal peptide (MELLNGTGLWSM) instead of the human-type (MGLEALVPLAVIV), and showed enantioselectivity of [(+)-BTL < (-)-BTL] for the rate of BTL 4-hydroxylation. In contrast, enantioselectivity [(+)-BTL > (-)-BTL] for Hep G2-CYP2D6 (CYP2D6-val) with a human-type N-terminal peptide that had a valine residue at 374, which corresponds to the methionine of the CYP2D6-met variant, was the same as that for human liver microsomes. We further confirmed that CYP2D6-met and CYP2D6-val expressed in human lymphoblastoid cells, both of which have methionine and valine, respectively, at position 374 and a human-type N-terminal peptide, exhibited the same enantioselectivities as those obtained from CYP2D6-met and CYP2D6-val expressed in the Hep G2 cell system. These results indicate that the amino acid at 374 of CYP2D6 is one of the key factors influencing the enantioselectivity of BTL 4-hydroxylation.

Functional importance of transmembrane helix 6 Trp(279) and exoloop 3 Val(299) of rat gonadotropin-releasing hormone receptor

Previous studies have established that the interaction of gonadotropin-releasing hormone (GnRH) with its receptor (GnRHR) would require partial entry of the N- and C-terminal regions of ligand into the transmembrane core. The functional significance of the conserved aromatic residue Trp(279) present in the transmembrane helix 6, and Val(299) located in exoloop 3 of the rat GnRHR was investigated by mutagenesis followed by expression in Chinese hamster ovary-K1 cells. Compared with wild-type, substitution of Trp(279) with Ser or Arg resulted in a marked reduction or total abolition, respectively, of ligand binding and, in both cases, abrogation of GnRH-induced inositol phosphate production. A total absence of functionality was observed when Val(299) was simply replaced with Ala. Mention should be made that an expression of all mutated and wild-type receptor proteins was observed. Interestingly, the double mutant [Trp(279)Arg/Val(299)Ala]GnRHR restored B(max) to wild type (504 +/- 43 versus 541 +/- 41 fmol/mg protein), but with a diminished affinity (4.95 +/- 1.05 versus 0.94 +/- 0.35 nM), and GnRH failed to induce inositol phosphate. No influence of the mutations was seen on internalization of the receptor. The three-dimensional model of GnRH binding to the rat GnRHR was built predicting that Trp(279) is buried at 20 A in the transmembrane core of the receptor, directly in contact with Trp(3) of GnRH. In contrast, Val(299) is located in a region that cannot be precisely defined at the extracellular end of transmembrane helix 7. Although models cannot provide any clue concerning the observed interactivity between the two distal residues, altogether these data reveal the functional importance of both GnRHR Trp(279) and Val(299) and suggest that Trp(279), interacting with GnRH Trp(3), represents the bottom of the binding pocket.

Valine 571 functions as a regional organizer in programming the glucocorticoid receptor for differential binding of glucocorticoids and mineralocorticoids

The glucocorticoid receptor (GR) interacts specifically with glucocorticoids, whereas its closest relative, the mineralocorticoid receptor (MR), interacts with both glucocorticoids and mineralocorticoids, such as aldosterone. To investigate the mechanism underlying the glucocorticoid/mineralocorticoid specificity of the GR, we used a yeast model system to screen for GR ligand-binding domain mutants, substituted with MR residues in the segment 565-574, that can be efficiently activated by aldosterone. In all such increased activity mutants, valine 571 was replaced by methionine, even though most mutants also contained substitutions of other residues with their MR counterparts. Further analysis in yeast and COS-7 cells has revealed that the identity of residue 571 determines the behavior of other MR substituted residues in the 565-574 segment. Generally, MR substitutions in this region are only consistent with aldosterone binding if residue 571 is also replaced with methionine (MR conformation). If residue 571 is valine (GR conformation), most other MR substitution mutants drastically reduce interaction with both mineralocorticoid and glucocorticoid hormones. Based on these functional data, we hypothesize that residue 571 functions as a regional organizer involved in discriminating between glucocorticoid and mineralocorticoid hormones. We have used a molecular model of the GR ligand-binding domain in an attempt to interpret our functional data in structural terms.

Val 70, Phe 72 and the last seven amino acid residues of C-terminal are essential to the function of norepinephrine transporter

The norepinephrine transporter(NET) is a member of the Na+/Cl- dependent neurotransmitter transporter family and constitutes the target of several clinically important antidepressants. To delineate the critical amino acid residues and the function of C-terminal in regulating transport activity of NET, here we constructed two site mutants (V70F, F72V; V70I, F72V) and one C-terminal truncated mutant (delta 611-617). The wild type and mutants of NET were expressed in Xenopus oocytes by injection of their cRNA. We found that all of these mutants lost their transport activity. These results indicate that the amino acid residues of V70 and F72, and the last seven amino acids of C-terminal are essential to the transport activity of NET.

Mossy fibre innervation is not required for the development of kainic acid toxicity in organotypic hippocampal slice cultures

The glutamate analogue kainic acid (KA) generates convulsions when applied systemically or directly into the brain and produces lesions comparable to those seen in Ammon's horn sclerosis, observed in many patients with temporal lobe epilepsy. The neurotoxic actions of KA in-vivo appear to be mediated by a combination of direct effects on neurons and indirect effects mediated by seizures. Understanding the contribution of both direct and indirect effects of KA towards neuronal cell death is important for elucidating excitotoxic mechanisms, which may represent a common final pathway in a variety of neurodegenerative disorders including stroke, traumatic brain injury and epilepsy. We have investigated the effects of mossy fibre innervation on the development of KA toxicity in organotypic hippocampal slice cultures in order to assess the role of this input pathway on the specific toxicity of KA toward CA3 pyramidal neurones in vitro.

Valine substituted winter flounder 'antifreeze': preservation of ice growth hysteresis

Three mutant polypeptides of the type I 37-residue winter flounder 'antifreeze' protein have been synthesized. All four threonine residues in the native peptide were been mutated to serine, valine and glycine respectively and two additional salt bridges were incorporated into the sequences in order to improve aqueous solubility. The peptides were analyzed by nanoliter osmometry, the 'ice hemisphere' test, the 'crystal habit' test, measurement of ice growth hysteresis and CD spectroscopy. While the valine and serine mutants retain the alpha-helical structure, only the valine mutant retains 'antifreeze' activity similar to that of the native protein. These data show that the threonine hydroxyl groups do not play a crucial role in the accumulation of the native 'antifreeze' protein at the ice/water interface and the inhibition of ice growth below the equilibrium melting temperature.

The roles of valine 208 and histidine 211 in ligand binding and receptor function of the ovine Mel1a beta melatonin receptor

Site-directed mutagenesis was used to study two residues, valine 208 and histidine 211, in transmembrane domain 5 of the ovine Mel1a beta melatonin receptor. A series of 4 mutants were constructed (V208A, V208L, H211F, H211L), and each engineered to contain a FLAG-epitope. Immunocytochemistry demonstrated that all the mutants were expressed in COS-7 cells at levels comparable to the FLAG-epitope tagged wild-type Mel1a beta receptor (approximately 120 fmol/mg protein). Ligand binding revealed however that all mutants had reduced affinities for 2-[125I]-iodomelatonin (Kd wild-type 139 pM, Kd mutants 320 to 989 pM). Competition studies, with a series of melatonin analogues, identified a probable interaction between histidine 211 and the 5-methoxy group of melatonin. The wild-type receptor and both valine 208 mutants displayed a dose-dependent melatonin mediated inhibition of cyclic AMP levels in HEK293 cells, with IC50 values in the same rank-order as their melatonin binding affinities. Both H211F and H211L, however, did not display any melatonin mediated effects and may suggest that histidine 211 is critical for melatonin mediated receptor activation.