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D C Wiley

Publications and source records attributed to D C Wiley.

197 records · Page 11Linked to original sources
PubMed1974

Complex of aspartate carbamoyltransferase from Escherichia coli with its allosteric inhibitor, cytidine triphosphate: electron density at 5.9-angstroms resolution.

Following our earlier determination of the three-dimensional structure of aspartate carbamoyltransferase (EC 2.1.3.2; carbamoylphosphate: L-aspartate carbamoyltransferase) to 5.5-A resolution [S. G. Warren, B. F. P. Edwards, D. R. Evans, D. C. Wiley & W. N. Lipscomb (1973) Proc. Nat. Acad. Sci. USA 70, 1117-1121], we report here, from a different crystal form, the three-dimensional structure at 5.9 A of this enzyme complexed with its allosteric inhibitor, cytidine triphosphate. Location of the major binding site of this inhibitor within each of the six regulatory chains is made secure by comparison of these results with those obtained upon binding of 5-iodocytidine triphosphate to the enzyme. Conformational changes in the aspartate carbamoyltransferase molecule when this inhibitor binds are described briefly at 5.9-A resolution.

Allosteric Regulation↗
PubMed1973

Aqueous central cavity in aspartate transcarbamylase from Escherichia coli.

A three-dimensional x-ray diffraction study of aspartate transcarbamylase to 5.5-angstrom resolution, with the aid of four isomorphous heavy atom derivatives, indicates the presence of a central aqueous cavity approximating an oblate spheroid about 25 by 50 by 50 angstroms in dimension, within a molecule about 90 by 110 by 110 angstroms in largest dimensions.

Aspartate Carbamoyltransferase↗
PubMed1973

Aspartate transcarbamoylase from Escherichia coli: electron density at 5.5 A resolution.

The allosteric enzyme, aspartate transcarbamoylase (EC 2.1.3.2), has previously been shown in our x-ray diffraction studies to have D(3)-32 symmetry. There are six catalytic (C) and six regulatory (R) chains in the molecular complex (R(6)C(6)). Our three-dimensional x-ray diffraction study of this enzyme (R32, a = 131 A, c = 200 A) at 5.5 A resolution shows a spatial arrangement of the two catalytic trimers C(3) above and below an equatorial belt of three regulatory dimers R(2). The molecule is about 110 x 110 x 90 A in largest dimensions, and is shown here to contain a large central aqueous cavity about 50 x 50 x 25 A in size. Location of the single sulfhydryl of each catalytic chain, and correlation of its reactivity with enzymatic activity in the molecule, suggests that the nearby active sites are most probably accessible from the central cavity, but probably not directly from the external solution. The most obvious access to the central cavity consists of six channels, each about 15 A in diameter, near the regulatory region. A component of the regulatory mechanism may be modulation of access of substrates through these channels.

Allosteric Regulation↗
PubMedDate not supplied

Crystallization of HLA-DR antigens.

The class II major histocompatibility antigens HLA-DR1, DR2, DR3, DR4, DR7 and DR8 were purified by immunoaffinity chromatography from homozygous human B lymphoblastoid cell lines. The purified, detergent-soluble molecules were cleaved with the protease papain to remove the hydrophobic transmembrane regions and cytoplasmic tails. Crystals were obtained for each of the papain-solubilized fragments. DR1 crystallized under a variety of different conditions, resulting in two different orthorhombic crystal forms, one of which diffracts as far as 3.5A. Crystals of DR2, DR3, DR4 and DR8 have the same unit cell dimensions as the DR1 crystals, and crystals of DR3 and DR4 have the same diffracting power as the DR1 crystals. The best DR7 crystals obtained thus far are hexagonal and diffract to only about 8A. Crystals of similar hexagonal form have also been observed for most of the other DR subsets.

Alleles↗
PubMedDate not supplied

Single amino acid substitutions in influenza haemagglutinin change receptor binding specificity.

The haemagglutinin (HA) glycoproteins of influenza virus membranes are responsible for binding viruses to cells by interacting with membrane receptor molecules which contain sialic acid (for review see ref. 1). This interaction is known to vary in detailed specificity for different influenza viruses (see, for example, refs 2-4) and we have attempted to identify the sialic acid binding site of the haemagglutinin by comparing the amino acid sequences of haemagglutinins with different binding specificities. We present here evidence that haemagglutinins which differ in recognizing either NeuAc alpha 2 leads to 3Gal- or NeuAc alpha 2 leads to 6Gal- linkages in glycoproteins also differ at amino acid 226 of HA1. This residue is located in a pocket on the distal tip of the molecule, an area previously proposed from considerations of the three-dimensional structure of the haemagglutinin to be involved in receptor binding.

Amino Acid Sequence↗
PubMedDate not supplied

6 A-resolution X-ray structure of a variable surface glycoprotein from Trypanosoma brucei.

The variable surface glycoprotein (VSG) is the predominant component of the surface coat of the African trypanosome. The expression of antigenically distinct VSGs on minor populations during infection allows the parasite to escape the host immune response. Purification of the protein is facilitated by the enzymatic release of a soluble form of VSG (sVSG) which occurs on cell lysis. The soluble form is a dimer with an approximate molecular weight of 120,000-130,000. Partial proteolysis of sVSG reveals a protease-sensitive link between an amino-terminal domain which comprises about two-thirds of the molecule, and a C-terminal domain which contains the membrane attachment site. We have obtained crystals suitable for high-resolution structural analysis from preparations of three sVSG: MITat 1.2, ILTat 1.25 and ILTat 1.22. The crystal structure of the dimer of the MITat 1.2 amino-terminal domain has been solved to 6 A resolution. We report here that the dimer is an unusual 90 A rod-like molecule composed of a helical bundle of at least four 80 A-long alpha-helices.

Animals↗
PubMedDate not supplied

Three-dimensional structure of an antigenic mutant of the influenza virus haemagglutinin.

Antigenic variation in the haemagglutinin (HA) glycoprotein of influenza virus is associated with recurrent epidemics of respiratory disease in man (for review see ref. 1). We have examined the size of structural changes necessary to alter the antigenicity of HA by determining the three-dimensional structure of the HA from an antigenic mutant containing a single amino acid substitution which was selected by growth of virus in the presence of monoclonal antibodies. Here we present evidence that the simple addition of an amino acid side chain which results in only minor local distortions of the structure of the HA is sufficient structural alteration for a virus to escape neutralization by a monoclonal antibody. Our results also demonstrate that single amino acid substitutions can cause only local changes in the HA structure, verifying the assumption made in several studies to locate antigenic sites on the HA and other molecules, and indicate that proposals of large conformational changes to account for variations in HA antigenicity are unnecessary in this case. The structure of the variant antigen has independently been successfully predicted (M. Karplus, personal communication).

Amino Acid Sequence↗
PubMedDate not supplied

Two variant surface glycoproteins of Trypanosoma brucei of different sequence classes have similar 6 A resolution X-ray structures.

Antigenic variation in the African trypanosome is mediated through changes in the composition of the surface coat. By controlling expression of the major surface protein, the variant surface glycoprotein (VSG), from a repertoire of perhaps 1,000 different genes the organisms exhibit a series of antigenically distinct coats and evade the host's immune system. We have determined the 6 A resolution structure of a T. brucei variant surface glycoprotein, ILTat 1.24, using X-ray crystallography. The crystallized protein consists of the N-terminal two-thirds of the intact VSG which has a relative molecular mass (Mr) of 60,000 (60K). The structure, which includes a 90 A long alpha-helical bundle, is strikingly similar to that of the N-terminal fragment of VSG MITat 1.2 (ref. 4). Although most known VSG sequences show little similarity of primary sequence in the N-terminal domain, the similarity between the structure of a Class I (ILTat 1.24) and a Class II (MITat 1.2) VSG antigen suggests that VSGs may share a common tertiary structure.

Animals↗
PubMedDate not supplied

Structure of the human class I histocompatibility antigen, HLA-A2.

The class I histocompatibility antigen from human cell membranes has two structural motifs: the membrane-proximal end of the glycoprotein contains two domains with immunoglobulin-folds that are paired in a novel manner, and the region distal from the membrane is a platform of eight antiparallel beta-strands topped by alpha-helices. A large groove between the alpha-helices provides a binding site for processed foreign antigens. An unknown 'antigen' is found in this site in crystals of purified HLA-A2.

Antigens↗
PubMedDate not supplied

The foreign antigen binding site and T cell recognition regions of class I histocompatibility antigens.

Most of the polymorphic amino acids of the class I histocompatibility antigen, HLA-A2, are clustered on top of the molecule in a large groove identified as the recognition site for processed foreign antigens. Many residues critical for T-cell recognition of HLA are located in this site, in positions allowing them to serve as ligands to processed antigens. These findings have implications for how the products of the major histocompatibility complex (MHC) recognize foreign antigens.

Antigens↗
PubMedDate not supplied

Structural basis for membrane fusion by enveloped viruses.

Enveloped viruses such as HIV-1, influenza virus, and Ebola virus express a surface glycoprotein that mediates both cell attachment and fusion of viral and cellular membranes. The membrane fusion process leads to the release of viral proteins and the RNA genome into the host cell, initiating an infectious cycle. This review focuses on the HIV-1 gp41 membrane fusion protein and discusses the structural similarities of viral membrane fusion proteins from diverse families such as Retroviridae (HIV-1), Orthomyxoviridae (influenza virus), and Filoviridae (Ebola virus). Their structural organization suggests that they have all evolved to use a similar strategy to promote fusion of viral and cellular membranes. This observation led to the proposal of a general model for viral membrane fusion, which will be discussed in detail.

Animals↗