Structure of the influenza virus glycoprotein antigen neuraminidase at 2.9 A resolution

The influenza virus neuraminidase glycoprotein is a tetramer with a box-shaped head, 100 X 100 X 60 A, attached to a slender stalk. The three-dimensional structure of neuraminidase heads shows that each monomer is composed of six topologically identical beta-sheets arranged in a propeller formation. The tetrameric enzyme has circular 4-fold symmetry stabilized in part by metal ions bound on the symmetry axis. Sugar residues are attached to four of the five potential glycosylation sequences, and in one case contribute to the interaction between subunits in the tetramer.

Structure of the catalytic and antigenic sites in influenza virus neuraminidase

The catalytic sites of influenza virus neuraminidase are located on the upper corners of the box-shaped tetramer that forms the head of the molecule. Antigenic determinants form a nearly-continuous surface across the top of the monomer encircling the catalytic site. Approximately the same number of amino acid sequence changes occurred in these determinants between the years 1968 and 1975 as occurred in the antigenic sites of influenza virus haemagglutinin in the same period.

Three-dimensional structure of a complex of antibody with influenza virus neuraminidase

The structure of a complex between influenza virus neuraminidase and an antibody displays features inconsistent with the inflexible 'lock and key' model of antigen-antibody binding. The structure of the antigen changes on binding, and that of the antibody may also change; the interaction therefore has some of the character of a handshake.

The structure of the complex between influenza virus neuraminidase and sialic acid, the viral receptor

Crystallographic studies of neuraminidase-sialic acid complexes indicate that sialic acid is distorted on binding the enzyme. Three arginine residues on the enzyme interact with the carboxylate group of the sugar which is observed to be equatorial to the saccharide ring as a consequence of its distorted geometry. The glycosidic oxygen is positioned within hydrogen-bonding distance of Asp-151, implicating this residue in catalysis.

Three-dimensional structure of the neuraminidase of influenza virus A/Tokyo/3/67 at 2.2 A resolution

An atomic model of the tetrameric surface glycoprotein neuraminidase of influenza virus A/Tokyo/3/67 has been built and refined based on X-ray diffraction data at 2.2 A resolution. The crystallographic residual is 0.21 for data between 6 and 2.2 A resolution and the r.m.s. deviations from ideal geometry are 0.02 A for bond lengths and 3.9 degrees for bond angles. The model includes amino acid residues 83 to 469, four oligosaccharide structures N-linked at asparagine residues 86, 146, 200 and 234, a single putative Ca2+ ion site, and 85 water molecules. One of the oligosaccharides participates in a novel crystal contact. The folding pattern is a beta-sheet propeller as described earlier and details of the intramolecular interactions between the six beta-sheets are presented. Strain-invariant residues are clustered around the propeller axis on the upper surface of the molecule where they line the wall of a cavity into which sialic has been observed to bind. Strain-variable residues implicated in binding to antibodies surround this site.

Three-dimensional structure of a barley beta-D-glucan exohydrolase, a family 3 glycosyl hydrolase

BACKGROUND

Cell walls of the starchy endosperm and young vegetative tissues of barley (Hordeum vulgare) contain high levels of (1-->3,1-->4)-beta-D-glucans. The (1-->3,1-->4)-beta-D-glucans are hydrolysed during wall degradation in germinated grain and during wall loosening in elongating coleoptiles. These key processes of plant development are mediated by several polysaccharide endohydrolases and exohydrolases.

RESULTS

. The three-dimensional structure of barley beta-D-glucan exohydrolase isoenzyme ExoI has been determined by X-ray crystallography. This is the first reported structure of a family 3 glycosyl hydrolase. The enzyme is a two-domain, globular protein of 605 amino acid residues and is N-glycosylated at three sites. The first 357 residues constitute an (alpha/beta)8 TIM-barrel domain. The second domain consists of residues 374-559 arranged in a six-stranded beta sandwich, which contains a beta sheet of five parallel beta strands and one antiparallel beta strand, with three alpha helices on either side of the sheet. A glucose moiety is observed in a pocket at the interface of the two domains, where Asp285 and Glu491 are believed to be involved in catalysis.

CONCLUSIONS

The pocket at the interface of the two domains is probably the active site of the enzyme. Because amino acid residues that line this active-site pocket arise from both domains, activity could be regulated through the spatial disposition of the domains. Furthermore, there are sites on the second domain that may bind carbohydrate, as suggested by previously published kinetic data indicating that, in addition to the catalytic site, the enzyme has a second binding site specific for (1-->3, 1-->4)-beta-D-glucans.

Dihydropyrancarboxamides related to zanamivir: a new series of inhibitors of influenza virus sialidases. 2. Crystallographic and molecular modeling study of complexes of 4-amino-4H-pyran-6-carboxamides and sialidase from influenza virus types A and B

The first paper in this series (see previous article) described structure-activity studies of carboxamide analogues of zanamivir binding to influenza virus sialidase types A and B and showed that inhibitory activity of these compounds was much greater against influenza A enzyme. To understand the large differences in affinities, a number of protein-ligand complexes have been investigated using crystallography and molecular dynamics. The crystallographic studies show that the binding of ligands containing tertiary amide groups is accompanied by the formation of an intramolecular planar salt bridge between two amino acid residues in the active site of the enzyme. It is proposed that the unexpected strong binding of these inhibitors is a result of the burial of hydrophobic surface area and salt-bridge formation in an environment of low dielectric. In sialidase from type A virus, binding of the carboxamide moeity and salt-bridge formation have only a minor effect on the positions of the surrounding residues, whereas in type B enzyme, significant distortion of the protein is observed. The results suggest that the decreased affinity in enzyme from influenza B is directly correlated with the small changes that occur in the amino acid residue interactions accompanying ligand binding. Molecular dynamics calculations have shown that the tendency for salt-bridge formation is greater in influenza A sialidase than influenza B sialidase and that this tendency is a useful descriptor for the prediction of inhibitor potency.

Refined crystal structure of the influenza virus N9 neuraminidase-NC41 Fab complex

The crystal structure of the complex between neuraminidase from influenza virus (subtype N9 and isolated from an avian source) and the antigen-binding fragment (Fab) of monoclonal antibody NC41 has been refined by both least-squares and simulated annealing methods to an R-factor of 0.191 using 31,846 diffraction data in the resolution range 8.0 to 2.5 A. The resulting model has a root-mean-square deviation from ideal bond-length of 0.016 A. One fourth of the tetrameric complex comprises the crystallographic model, which has 6577 non-hydrogen atoms and consists of 389 protein residues and eight carbohydrate residues in the neuraminidase, 214 residues in the Fab light chain, and 221 residues in the heavy chain. One putative Ca ion buried in the neuraminidase, and 73 water molecules, are also included. A remarkable shape complementarity exists between the interacting surfaces of the antigen and the antibody, although the packing density of atoms at the interface is somewhat looser than in the interior of a protein. Similarly, there is a high degree of chemical complementarity between the antigen and antibody, mediated by one buried salt-link, two solvated salt-links and 12 hydrogen bonds. The antibody-binding site on neuraminidase is discontinuous and comprises five chain segments and 19 residues in contact, whilst 33 neuraminidase residues in eight segments have 899 A2 of surface area buried by the interaction (to a 1.7 A probe), including two hexose units. Seventeen residues in NC41 Fab lying in five of the six complementarity determining regions (CDRs) make contact with the neuraminidase and 36 antibody residues in seven segments have 916 A2 of buried surface area. The interface is more extensive than those of the three lysozyme-Fab complexes whose crystal structures have been determined, as judged by buried surface area and numbers of contact residues. There are only small differences (less than 1.5 A) between the complexed and uncomplexed neuraminidase structures and, at this resolution and accuracy, those differences are not unequivocal. The main-chain conformations of five of the CDRs follow the predicted canonical structures. The interface between the variable domains of the light and heavy chains is not as extensive as in other Fabs, due to less CDR-CDR interaction in NC41. The first CDR on the NC41 Fab light chain is positioned so that it could sterically hinder the approach of small as well as large substrates to the neuraminidase active-site pocket, suggesting a possible mechanism for the observed inhibition of enzyme activity by the antibody.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug design against a shifting target: a structural basis for resistance to inhibitors in a variant of influenza virus neuraminidase

BACKGROUND

Inhibitors of the influenza virus neuraminidase have been shown to be effective antiviral agents in humans. Several studies have reported the selection of novel influenza strains when the virus is cultured with neuraminidase inhibitors in vitro. These resistant viruses have mutations either in the neuraminidase or in the viral haemagglutinin. Inhibitors in which the glycerol sidechain at position 6 of 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (Neu5Ac2en) has been replaced by carboxamide-linked hydrophobic substituents have recently been reported and shown to select neuraminidase variants. This study seeks to clarify the structural and functional consequences of replacing the glycerol sidechain of the inhibitor with other chemical constituents.

RESULTS

The neuraminidase variant Arg292-->Lys is modified in one of three arginine residues that encircle the carboxylate group of the substrate. The structure of this variant in complex with the carboxamide inhibitor used for its selection, and with other Neu5Ac2en analogues, is reported here at high resolution. The structural consequences of the mutation correlate with altered inhibitory activity of the compounds compared with wild-type neuraminidase.

CONCLUSIONS

The Arg292-->Lys variant of influenza neuraminidase affects the binding of substrate by modification of the interaction with the substrate carboxylate. This may be one of the structural correlates of the reduced enzyme activity of the variant. Inhibitors that have replacements for the glycerol at position 6 are further affected in the Arg292-->Lys variant because of structural changes in the binding site that apparently raise the energy barrier for the conformational change in the enzyme required to accommodate such inhibitors. These results provide evidence that a general strategy for drug design when the target has a high mutation frequency is to design the inhibitor to be as closely related as possible to the natural ligands of the target.

Mutations in a conserved residue in the influenza virus neuraminidase active site decreases sensitivity to Neu5Ac2en-derived inhibitors

The influenza virus neuraminidase (NA)-specific inhibitor zanamivir (4-guanidino-Neu5Ac2en) is effective in humans when administered topically within the respiratory tract. The search for compounds with altered pharmacological properties has led to the identification of a novel series of influenza virus NA inhibitors in which the triol group of zanamivir has been replaced by a hydrophobic group linked by a carboxamide at the 6 position (6-carboxamide). NWS/G70C variants generated in vitro, with decreased sensitivity to 6-carboxamide, contained hemagglutinin (HA) and/or NA mutations. HA mutants bound with a decreased efficiency to the cellular receptor and were cross-resistant to all the NA inhibitors tested. The NA mutation, an Arg-to-Lys mutation, was in a previously conserved site, Arg292, which forms part of a triarginyl cluster in the catalytic site. In enzyme assays, the NA was equally resistant to zanamivir and 4-amino-Neu5Ac2en but showed greater resistance to 6-carboxamide and was most resistant to a new carbocyclic NA inhibitor, GS4071, which also has a hydrophobic side chain at the 6 position. Consistent with enzyme assays, the lowest resistance in cell culture was seen to zanamivir, more resistance was seen to 6-carboxamide, and the greatest resistance was seen to GS4071. Substrate binding and enzyme activity were also decreased in the mutant, and consequently, virus replication in both plaque assays and liquid culture was compromised. Altered binding of the hydrophobic side chain at the 6 position or the triol group could account for the decreased binding of both the NA inhibitors and substrate.

Three-dimensional structure of the complex of 4-guanidino-Neu5Ac2en and influenza virus neuraminidase

The three-dimensional X-ray structure of a complex of the potent neuraminidase inhibitor 4-guanidino-Neu5Ac2en and influenza virus neuraminidase (Subtype N9) has been obtained utilizing diffraction data to 1.8 A resolution. The interactions of the inhibitor, solvent water molecules, and the active site residues have been accurately determined. Six water molecules bound in the native structure have been displaced by the inhibitor, and the active site residues show no significant conformational changes on binding. Sialic acid, the natural substrate, binds in a half-chair conformation that is isosteric to the inhibitor. The conformation of the inhibitor in the active site of the X-ray structure concurs with that obtained by theoretical calculations and validates the structure-based design of the inhibitor. Comparison of known high-resolution structures of neuraminidase subtypes N2, N9, and B shows good structural conservation of the active site protein atoms, but the location of the water molecules in the respective active sites is less conserved. In particular, the environment of the 4-guanidino group of the inhibitor is strongly conserved and is the basis for the antiviral action of the inhibitor across all presently known influenza strains. Differences in the solvent structure in the active site may be related to variation in the affinities of inhibitors to different subtypes of neuraminidase.

Three-dimensional structures of two plant beta-glucan endohydrolases with distinct substrate specificities

The three-dimensional structures of (1-->3)-beta-glucanase (EC 3.2.1.39) isoenzyme GII and (1-->3,1-->4)-beta-glucanase (EC 3.2.1.73) isoenzyme EII from barley have been determined by x-ray crystallography at 2.2- to 2.3-A resolution. The two classes of polysaccharide endohydrolase differ in their substrate specificity and function. Thus, the (1-->3)-beta-glucanases, which are classified amongst the plant "pathogenesis-related proteins," can hydrolyze (1-->3)- and (1-->3,1-->6)-beta-glucans of fungal cell walls and may therefore contribute to plant defense strategies, while the (1-->3,1-->4)-beta-glucanases function in plant cell wall hydrolysis during mobilization of the endosperm in germinating grain or during the growth of vegetative tissues. Both enzymes are alpha/beta-barrel structures. The catalytic amino acid residues are located within deep grooves which extend across the enzymes and which probably bind the substrates. Because the polypeptide backbones of the two enzymes are structurally very similar, the differences in their substrate specificities, and hence their widely divergent functions, have been acquired primarily by amino acid substitutions within the groove.

Generation and characterization of an influenza virus neuraminidase variant with decreased sensitivity to the neuraminidase-specific inhibitor 4-guanidino-Neu5Ac2en

A variant of the influenza virus NWS/G70C has been generated which has decreased sensitivity in vitro to the neuraminidase-specific inhibitor, 4-guanidino-Neu5Ac2en. The virus is 1000-fold less sensitive to the 4-guanidino-Neu5Ac2en in a plaque assay, but only 10-fold less sensitive to 4-amino-Neu5Ac2en. In an enzyme inhibition assay 250-fold more drug was needed to achieve inhibition comparable to that observed with the parent virus. In contrast to the plaque assay, the virus was fully sensitive to 4-amino-Neu5Ac2en in the enzyme inhibition assay. Kinetic analysis of 4-guanidino-Neu5Ac2en binding demonstrated that the variant no longer exhibited the slow binding characteristic seen with the parent and other influenza viruses and inhibition by Neu5Ac2en was also decreased. However, binding to 4-amino-Neu5Ac2en remained the same as the parent. Sequence analysis of this virus revealed a mutation at a previously conserved site in the enzyme active site of the neuraminidase, Glu 119 to Gly. Crystallographic analysis of the mutant neuraminidase with and without bound inhibitor confirmed this mutation and suggested that the reduced affinity for the 4-guanidino-Neu5Ac2en derives partly from the loss of a stabilizing interaction between the guanidino moiety and the carboxylate at residue 119, and partly from alterations to the solvent structure of the active site.

VDAC is a conserved element of death pathways in plant and animal systems

Programmed cell death (PCD) is very much a part of plant life, although the underlying mechanisms are not so well understood as in animals. In animal cells, the voltage-dependent anion channel (VDAC), a major mitochondrial outer membrane transporter, plays an important role in apoptosis by participating in the release of intermembrane space proteins. To characterize plant PCD pathways by investigating the function of putative components in a mammalian apoptotic context, we have overexpressed a rice VDAC (osVDAC4) in the Jurkat T-cell line. Overexpression of osVDAC4 induces apoptosis, which can be blocked by Bcl-2 and the VDAC inhibitor DIDS. Modifying endogenous VDAC function by DIDS and hexokinase II (HxKII) in Jurkat cells inhibits mitochondria-mediated apoptotic pathways. Finally, we show that DIDS also abrogates heat-induced PCD in cucumber cotyledons. Our data suggest that VDAC is a conserved mitochondrial element of the death machinery in both plant and animal cells.

Structural evidence for a second sialic acid binding site in avian influenza virus neuraminidases

The x-ray structure of a complex of sialic acid (Neu5Ac) with neuraminidase N9 subtype from A/tern/Australia/G70C/75 influenza virus at 4 degrees C has revealed the location of a second Neu5Ac binding site on the surface of the enzyme. At 18 degrees C, only the enzyme active site contains bound Neu5Ac. Neu5Ac binds in the second site in the chair conformation in a similar way to which it binds to hemagglutinin. The residues that interact with Neu5Ac at this second site are mostly conserved in avian strains, but not in human and swine strains, indicating that it has some as-yet-unknown biological function in birds.

Structural evidence for evolution of shark Ig new antigen receptor variable domain antibodies from a cell-surface receptor

The Ig new antigen receptors (IgNARs) are single-domain antibodies found in the serum of sharks. Here, we report 2.2- and 2.8-A structures of the type 2 IgNAR variable domains 12Y-1 and 12Y-2. Structural features include, first, an Ig superfamily topology transitional between cell adhesion molecules, antibodies, and T cell receptors; and, second, a vestigial complementarity-determining region 2 at the "bottom" of the molecule, apparently discontinuous from the antigen-binding paratope and similar to that observed in cell adhesion molecules. Thus, we suggest that IgNARs originated as cell-surface adhesion molecules coopted to the immune repertoire and represent an evolutionary lineage independent of variable heavy chain/variable light chain type antibodies. Additionally, both 12Y-1 and 12Y-2 form unique crystallographic dimers, predominantly mediated by main-chain framework interactions, which represent a possible model for primordial cell-based interactions. Unusually, the 12Y-2 complementarity-determining region 3 also adopts an extended beta-hairpin structure, suggesting a distinct selective advantage in accessing cryptic antigenic epitopes.

Structure of the extracellular domains of the human interleukin-6 receptor alpha -chain

Dysregulated production of IL-6 and its receptor (IL-6R) are implicated in the pathogenesis of multiple myeloma, autoimmune diseases and prostate cancer. The IL-6R complex comprises two molecules each of IL-6, IL-6R, and the signaling molecule, gp130. Here, we report the x-ray structure (2.4 A) of the IL-6R ectodomains. The N-terminal strand of the Ig-like domain (D(1)) is disulfide-bonded to domain D(2), and domains D(2) and D(3), the cytokine-binding domain, are structurally similar to known cytokine-binding domains. The head-to-tail packing of two closely associated IL-6R molecules observed in the crystal may be representative of the configuration of the physiological dimer of IL-6R and provides new insight into the architecture of the IL-6R complex.

Antigenic structure and variation in an influenza virus N9 neuraminidase

We previously determined, by X-ray crystallography, the three-dimensional structure of a complex between influenza virus N9 neuraminidase (NA) and the Fab fragments of monoclonal antibody NC-41 [P. M. Colman, W. G. Laver, J. N. Varghese, A. T. Baker, P. A. Tulloch, G. M. Air, and R. G. Webster, Nature (London) 326:358-363, 1987]. This antibody binds to an epitope on the upper surface of the NA which is made up of four polypeptide loops over an area of approximately 600 A2 (60 nm2). We now describe properties of NC-41 and other monoclonal antibodies to N9 NA and the properties of variants selected with these antibodies (escape mutants). All except one of the escape mutants had single amino acid sequence changes which affected the binding of NC-41 and which therefore are located within the NC-41 epitope. The other one had a change outside the epitope which did not affect the binding of any of the other antibodies. All the antibodies which selected variants inhibited enzyme activity with fetuin (molecular weight, 50,000) as the substrate, but only five, including NC-41, also inhibited enzyme activity with the small substrate N-acetylneuramin-lactose (molecular weight, 600). These five probably inhibited enzyme activity by distorting the catalytic site of the NA. Isolated, intact N9 NA molecules form rosettes in the absence of detergent, and these possess high levels of hemagglutinin activity (W.G. Laver, P.M. Colman, R.G. Webster, V.S. Hinshaw, and G.M. Air, Virology 137:314-323, 1984). The enzyme activity of N9 NA was inhibited efficiently by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, whereas hemagglutinin activity was unaffected. The NAs of several variants with sequence changes in the NC-41 epitope lost hemagglutinin activity without any loss of enzyme activity, suggesting that the two activities are associated with separate sites on the N9 NA head.

Sudden death among postoperative patients with tetralogy of Fallot: a follow-up study of 243 patients for an average of twelve years

Two hundred and forty-three patients were evaluated following total correction of tetralogy of Fallot with special emphasis on postoperative conduction disturbances and on the occurrence of sudden death. The average follow-up period was 12 years with a range of 6 1/2 to 16 1/2 years. Sudden death occurred in seven patients. Four deaths were among those with right bundle branch block pattern (RBBB) and three of the four had premature ventricular contractions (PVC) for more than one month postoperatively. PVCs were documented in ten of the 158 patients with RBBB; sudden death occurred in three (30%). Three of the ten (30%) patients with trifascicular block pattern (TB) died suddenly, while no deaths occurred in 24 patients with bifascicular block pattern (BB). Progression of RBBB to BB and TB occurred in 18 patients from one month to seven years postoperatively (58% of BB and 40% of TB). The risk of sudden death in patients with RBBB and PVCs following tetralogy repair is high and warrants consideration of suppressive therapy. TB also carries a high risk. The finding that RBBB may progress to BB or TB mandates long-term careful follow-up of all tetralogy patients with postoperative conduction disturbances.

Three-dimensional structure of neuraminidase of subtype N9 from an avian influenza virus

Neuraminidases from different subtypes of influenza virus are characterized by the absence of serological cross-reactivity and an amino acid sequence homology of approximately 50%. The three-dimensional structure of the neuraminidase antigen of subtype N9 from an avian influenza virus (A/tern/Australia/G70c/75) has been determined by X-ray crystallography and shown to be folded similarly to neuraminidase of subtype N2 isolated from a human influenza virus. This result demonstrates that absence of immunological cross-reactivity is no measure of dissimilarity of polypeptide chain folding. Small differences in the way in which the subunits are organized around the molecular fourfold axis are observed. Insertions and deletions with respect to subtype N2 neuraminidase occur in four regions, only one of which is located within the major antigenic determinants around the enzyme active site.

The three-dimensional structure of the seed storage protein phaseolin at 3 A resolution

The polypeptides of the trimeric seed storage protein phaseolin comprise two structurally similar units each made up of a beta-barrel and an alpha-helical domain. The beta-barrel has the 'jelly-roll' folding topology of the viral coat proteins and the alpha-helical domain shows structural similarity to the helix-turn-helix motif found in certain DNA-binding proteins.

Comparative modeling of the three-dimensional structures of family 3 glycoside hydrolases

There are approximately 100 known members of the family 3 group of glycoside hydrolases, most of which are classified as beta-glucosidases and originate from microorganisms. The only family 3 glycoside hydrolase for which a three-dimensional structure is available is a beta-glucan exohydrolase from barley. The structural coordinates of the barley enzyme is used here to model representatives from distinct phylogenetic clusters within the family. The majority of family 3 hydrolases have an NH(2)-terminal (alpha/beta)(8) barrel connected by a short linker to a second domain, which adopts an (alpha/beta)(6) sandwich fold. In two bacterial beta-glucosidases, the order of the domains is reversed. The catalytic nucleophile, equivalent to D285 of the barley beta-glucan exohydrolase, is absolutely conserved across the family. It is located on domain 1, in a shallow site pocket near the interface of the domains. The likely catalytic acid in the barley enzyme, E491, is on domain 2. Although similarly positioned acidic residues are present in closely related members of the family, the equivalent amino acid in more distantly related members is either too far from the active site or absent. In the latter cases, the role of catalytic acid is probably assumed by other acidic amino acids from domain 1.

Refined atomic structures of N9 subtype influenza virus neuraminidase and escape mutants

The crystal structure of the N9 subtype neuraminidase of influenza virus was refined by simulated annealing and conventional techniques to an R-factor of 0.172 for data in the resolution range 6.0 to 2.2 A. The r.m.s. deviation from ideal values of bond lengths is 0.014 A. The structure is similar to that of N2 subtype neuraminidase both in secondary structure elements and in their connections. The three-dimensional structures of several escape mutants of neuraminidase, selected with antineuraminidase monoclonal antibodies, are also reported. In every case, structural changes associated with the point mutation are confined to the mutation site or to residues that are spatially immediately adjacent to it. The failure of antisera to cross-react between N2 and N9 subtypes may be correlated with the absence of conserved, contiguous surface structures of area 700 A2 or more.

Analysis of inhibitor binding in influenza virus neuraminidase

2,3-didehydro-2-deoxy-N:-acetylneuraminic acid (DANA) is a transition state analog inhibitor of influenza virus neuraminidase (NA). Replacement of the hydroxyl at the C9 position in DANA and 4-amino-DANA with an amine group, with the intention of taking advantage of an increased electrostatic interaction with a conserved acidic group in the active site to improve inhibitor binding, significantly reduces the inhibitor activity of both compounds. The three-dimensional X-ray structure of the complexes of these ligands and NA was obtained to 1.4 A resolution and showed that both ligands bind isosterically to DANA. Analysis of the geometry of the ammonium at the C4 position indicates that Glu119 may be neutral when these ligands bind. A computational analysis of the binding energies indicates that the substitution is successful in increasing the energy of interaction; however, the gains that are made are not sufficient to overcome the energy that is required to desolvate that part of the ligand that comes in contact with the protein.

The role of maternal affect mirroring on social expectancies in three-month-old infants

The role of maternal affect mirroring on the development of prosocial behaviors and social expectancies was assessed in forty-one 2- to 3-month-old infants. Prosocial behavior was characterized as infants' positive behavior and increased attention toward their mothers. Social expectancies were defined as infants' expectancy for affective sharing. Mothers and infants were observed twice, approximately 1 week apart. During Visit 1, mothers and infants were videotaped while interacting over television monitors for 3 min. During Visit 2, infants engaged in a live, 3-min interaction with their mothers over television monitors (live condition) and they also viewed a replay of their mothers' interaction from the preceding week (replay condition). The order of conditions was counterbalanced. Maternal affect mirroring was measured according to the level of attention maintenance, warm sensitivity, and social responsiveness displayed. A natural split was observed with 58% of the mothers ranking high and 42% ranking low on these affect mirroring measures (HAM and LAM, respectively). Infants in the HAM group ranked high on prosocial behaviors and social expectancy--they discriminated between live and replay, conditions with smiles, vocalizations, and gazes. Infants in the LAM group ranked low on these variables--they gazed longer during the live condition than during the replay condition, but only when the live condition was presented first; however, they did not smile or vocalize more. These findings indicate that there is a relation between affect mirroring and social expectancies in infants.