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Biomedical subjects

A Wlodawer

Publications and source records attributed to A Wlodawer.

At least 19 recordsLinked to original sources
PubMed1999

Crystal structure of cyanovirin-N, a potent HIV-inactivating protein, shows unexpected domain swapping.

The crystal structure of cyanovirin-N (CV-N), a protein with potent antiviral activity, was solved at 1.5 A resolution by molecular replacement using as the search model the solution structure previously determined by NMR. The crystals belong to the space group P3221 with one monomer of CV-N in each asymmetric unit. The primary structure of CV-N contains 101 residues organized in two domains, A (residues 1 to 50) and B (residues 51 to 101), with a high degree of internal sequence and structural similarity. We found that under the conditions of the crystallographic experiments (low pH and 26 % isopropanol), two symmetrically related monomers form a dimer by domain swapping, such that domain A of one monomer interacts with domain B' of its crystallographic symmetry mate and vice versa. Because the two swapped domains are distant from each other, domain swapping does not result in additional intramolecular interactions. Even though one of the protein sample solutions that was used for crystallization clearly contained 100 % monomeric CV-N molecules, as judged by various methods, we were only able to obtain crystals containing domain-swapped dimers. With the exception of the unexpected phenomenon of domain swapping, the crystal structure of CV-N is very similar to the NMR structure, with a root-mean-square deviation of 0.55 A for the main-chain atoms, the best agreement reported to date for structures solved using both techniques.

Antiviral Agents↗
PubMed1999

Decamers observed in the crystals of bovine pancreatic trypsin inhibitor.

The structure of bovine pancreatic trypsin inhibitor (BPTI) has been solved at 2.1 A resolution in a new crystal form (space group P6422 with unit-cell dimensions a = b = 95.0, c = 158.1 A). The asymmetric unit is a pentamer, but a decamer is created by application of crystallographic symmetry. The decamer of BPTI is only the fourth such assembly reported to date in the Protein Data Bank.

Animals↗
PubMed1999

Crystal structures of catalytic core domains of retroviral integrases and role of divalent cations in enzymatic activity.

Crystal structures of the enzymatically competent catalytic domains of HIV-1 and ASV IN have been solved in the last few years. The structure of HIV-1 IN has been described only for apoenzyme and for a complex with Mg2+, whereas the structure of ASV IN has been presented as the apoenzyme, in the presence of divalent cations (Mn2+, Mg2+, Ca2+, Zn2+, and Cd2+), and with an inhibitor. A single ion of Mn2+, Mg2+, or Ca2+ interacts with the two aspartate side chains of the D,D(35)E catalytic center in octahedral coordination with four water molecules. However, two ions of Zn2+ or Cd2+ bind to the active site of IN with tetrahedral and octahedral coordination, respectively. Only small adjustments take place in the active site of ASV IN on binding of the metal cofactor(s), which are absolutely required for the activity of this enzyme. The placement of the side chains and metal ions in the active site is very similar to that observed even in distant members of this superfamily of polynucleotidyltransferases. Here the role of divalent cations in the enzymatic activity of IN and the search for inhibitors of this enzyme are discussed.

Amino Acid Sequence↗
PubMed1999

Total chemical synthesis and high-resolution crystal structure of the potent anti-HIV protein AOP-RANTES.

BACKGROUND: RANTES is a CC-type chemokine protein that acts as a chemoattractant for several kinds of leukocytes, playing an important pro-inflammatory role. Entry of human immunodeficiency virus-1 (HIV-1) into cells depends on the chemokine receptor CCR5. RANTES binds CCR5 and inhibits HIV-1 entry into peripheral blood cells. Interaction with chemokine receptors involves a distinct set of residues at the amino terminus of RANTES. This finding was utilized in the development of a chemically modified aminooxypentane derivative of RANTES, AOP-RANTES, that was originally produced from the recombinant protein using semisynthetic methods. RESULTS: AOP-RANTES has been produced by a novel total chemical synthesis that provides efficient, direct access to large amounts of this anti-HIV protein analog. The crystal structure of chemically synthesized AOP-RANTES has been solved and refined at 1.6 A resolution. The protein is a dimer, with the amino-terminal pentane oxime moiety clearly defined. CONCLUSIONS: Total chemical synthesis of AOP-RANTES provides a convenient method of producing the multi-milligram quantities of this protein needed to investigate the molecular basis of receptor binding and antiviral activity. This work provides the first truly high-resolution structure of a RANTES protein, although the structure of RANTES was known from previous nuclear magnetic resonance (NMR) determinations.

Amino Acid Sequence↗
PubMed1999

Purification of receptor complexes of interleukin-10 stoichiometry and the importance of deglycosylation in their crystallization.

Interleukin-10 (IL-10) is a pleiotropic immunosuppressive cytokine that has a wide range of effects in controlling inflammatory responses. Viral IL-10 (vIL-10) is a homologue of human IL-10 (hIL-10) produced by Epstein-Barr virus (EBV). Both hIL-10 and vIL-10 bind to the soluble extracellular fragment of the cytokine receptor IL-10R1 (shIL-10R1). The stoichiometry of the vIL-10 : shIL-10R1 complex has been found to be the same as hIL-10 : shIL-10R1, with two vIL-10 dimers binding to four shIL-10R1 monomers. Complexes of both hIL-10 and vIL-10 with glycosylated shIL-10R1 could not be crystallized. Controlled deglycosylation using peptide : N-glycosidase F and endo-beta-N-acetylglucosaminidase F3 resulted in the formation of crystals of both hIL-10 : shIL-10R1 and vIL-10 : shIL-10R1 complexes, indicating that the difficulty in the crystal formation was largely due to the presence of complex carbohydrate side chains. The availability of the structure of the ligand-receptor complexes should facilitate our understanding of the basis of the interaction between IL-10 and the IL-10 receptor.

Chromatography, Gel↗
PubMed1998

Structural basis for inactivating mutations and pH-dependent activity of avian sarcoma virus integrase.

Crystallographic studies of the catalytic core domain of avian sarcoma virus integrase (ASV IN) have provided the most detailed picture so far of the active site of this enzyme, which belongs to an important class of targets for designing drugs against AIDS. Recently, crystals of an inactive D64N mutant were obtained under conditions identical to those used for the native enzyme. Data were collected at different pH values and in the presence of divalent cations. Data were also collected at low pH for the crystals of the native ASV IN core domain. In the structures of native ASV IN at pH 6.0 and below, as well as in all structures of the D64N mutants, the side chain of the active site residue Asx-64 (Asx denotes Asn or Asp) is rotated by approximately 150 degrees around the Calpha---Cbeta bond, compared with the structures at higher pH. In the new structures, this residue makes hydrogen bonds with the amide group of Asn-160, and thus, the usual metal-binding site, consisting of Asp-64, Asp-121, and Glu-157, is disrupted. Surprisingly, however, a single Zn2+ can still bind to Asp-121 in the mutant, without restoration of the activity of the enzyme. These structures have elucidated an unexpected mechanism of inactivation of the enzyme by lowering the pH or by mutation, in which a protonated side chain of Asx-64 changes its orientation and interaction partner.

Amino Acid Sequence↗
PubMed1998

Transport and activation of the vacuolar aspartic proteinase phytepsin in barley (Hordeum vulgare L.).

The primary translation product of barley aspartic proteinase, phytepsin (EC 3.4.23.40), consists of a signal sequence, a propart, and mature enzyme forms. Here, we describe post-translational processing and activation of phytepsin during its transport to the vacuole in roots, as detected by using metabolic labeling and immunoprecipitation. After removal of the signal sequence, the glycosylated precursor of 53 kDa (P53) was produced and further processed to polypeptides of 31 and 15 kDa (P31 + P15) and, subsequently, to polypeptides of 26 and 9 kDa (P26 + P9), 45 min and 24 h after synthesis, respectively. The processing occurred in a late-Golgi compartment or post-Golgi compartment, because brefeldin A inhibited the processing, and P53 acquired partial endoglycosidase H resistance 30 min after synthesis, whereas P15 was completely resistant. The N-glycosylation inhibitor tunicamycin had no effect on transport, but the absence of glycans on P53 accelerated the proteolytic processing. Phytepsin was also expressed in baculovirus-infected insect cells. The recombinant prophytepsin underwent autoproteolytic activation in vitro and showed enzymatic properties similar to the enzyme purified from grains. However, a comparison of the in vitro/in vivo processing sites revealed slight differences, indicating that additional proteases are needed for the completion of the maturation in vivo.

Amino Acid Sequence↗
PubMed1998

Crystal structure of rabbit muscle creatine kinase.

The crystal structure of rabbit muscle creatine kinase, solved at 2.35 A resolution by X-ray diffraction methods, clearly identified the active site with bound sulfates surrounded by a constellation of arginine residues. The putative binding site of creatine, which is occupied by a sulfate group in this analysis, has been tentatively identified. The dimeric interface of the enzyme is held together by a small number of hydrogen bonds.

Animals↗
PubMed1998

Drug-resistant HIV-1 proteases identify enzyme residues important for substrate selection and catalytic rate.

A series of mutations, first identified in protease inhibitor-resistant HIV-1 viral isolates, were introduced into HIV-1 PR as individual substitutions. Mutants containing R8K, V32I, V82T, I84V, G48V/L90M, or V82T/I84V substitutions were analyzed for differences in substrate preference and catalytic efficiency using a set of single amino acid substituted HIV-1 CA-NCa cleavage site peptides. All mutants exhibited wild-type preference for large hydrophobic residues, especially Phe, in the P1' substrate position. Only the R8K and V32I mutants showed significant differences in subsite selection compared to wild-type enzyme. In a parallel study, the individual mutations R10K, L12V, I44V, A60M, I71V, and I108V were introduced into RSV PR. These amino acid positions are structurally equivalent to Arg8, Leu10, Val32, Met46, Ile54, and Ile84 in HIV-1 PR, respectively, which mutate in drug-resistance. The RSV R10K substitution significantly altered substrate specificity and catalytic rate, compared to wild-type, in a manner similar to that of the HIV-1 R8K mutant. Crystal structures of the RSV PR R10K, I44V, I71V, and Il08V mutant enzymes presented here indicate that each of these substitutions has little effect on the overall structure of the respective enzymes. Taken together, these data provide an explanation for the reported in vivo predilection for selection of large hydrophobic residues in the P1' substrate position of second locus mutations in the Gag polyprotein PR cleavage sites. The data also suggest that the selection of resistant enzymes is not simply limited to loss of binding to inhibitor but affects other steps in proteolysis.

Amino Acid Substitution↗
PubMed1998

Structure of the catalytic domain of avian sarcoma virus integrase with a bound HIV-1 integrase-targeted inhibitor.

The x-ray structures of an inhibitor complex of the catalytic core domain of avian sarcoma virus integrase (ASV IN) were solved at 1.9- to 2.0-A resolution at two pH values, with and without Mn2+ cations. This inhibitor (Y-3), originally identified in a screen for inhibitors of the catalytic activity of HIV type 1 integrase (HIV-1 IN), was found in the present study to be active against ASV IN as well as HIV-1 IN. The Y-3 molecule is located in close proximity to the enzyme active site, interacts with the flexible loop, alters loop conformation, and affects the conformations of active site residues. As crystallized, a Y-3 molecule stacks against its symmetry-related mate. Preincubation of IN with metal cations does not prevent inhibition, and Y-3 binding does not prevent binding of divalent cations to IN. Three compounds chemically related to Y-3 also were investigated, but no binding was observed in the crystals. Our results identify the structural elements of the inhibitor that likely determine its binding properties.

Avian Sarcoma Viruses↗
PubMed1998

Single amino acid substitutions at the N-terminus of a recombinant cytotoxic ribonuclease markedly influence biochemical and biological properties.

Onconase is a cytotoxic ribonuclease with antitumor properties. A semisynthetic gene encoding the entire protein sequence was constructed by fusing oligonucleotides coding for the first 15 and the last 6 of the 104 amino acids to a genomic clone that encoded the remaining amino acid residues [Newton, D. L., et al. (1997) Protein Eng. 10, 463-470]. The resulting protein product expressed in Escherichia coli exhibited little enzymatic or cytotoxic activity due to the unprocessed N-terminal Met amino acid residue. In this study, we demonstrate that modification of the 5'-region of the gene to encode [Met-(-1)]Ser or [Met-(-1)]Tyr instead of the native pyroglutamate results in recombinant onconase derivatives with restored activities. [Met-(-1)]rOnc(E1S) was more active than [Met-(-1)]rOnc(E1Y) in all assays tested. Consistent with the action of native onconase, [Met-(-1)]rOnc(E1S) was a potent inhibitor of protein synthesis in the cell-free rabbit reticulocyte lysate assay, degrading tRNA at concentrations that correlated with inhibition of protein synthesis. An interesting difference between the recombinant onconase derivatives and the native protein was their susceptibility to inhibition by the major intracellular RNase inhibitor, PRI (onconase is refractory to PRI inhibition). [Met-(-1)]rOnc(E1S) and [Met-(-1)]rOnc(E1Y) inhibited protein synthesis in intact SF539 neuroblastoma cells with IC50's very similar to that of onconase (IC50 3.5, 10, and 10 microg/mL after 1 day and 0.16, 0.35, and 2.5 microg/mL after 5 days for onconase, [Met-(-1)]rOnc(E1S), and [Met-(-1)]rOnc(E1Y), respectively). Similar to that of onconase, cytotoxic activity of the recombinant derivatives was potentiated by monensin, NH4Cl, and retinoic acid. Brefeldin A completely blocked the enhancement of cytotoxicity caused by retinoic acid with all three proteins. Thus, drug-induced alterations of the intracellular trafficking of the recombinant derivatives also resembles that of onconase. Stability studies as assessed in serum-containing medium in the presence or absence of cells at 37 degreesC showed that the recombinant proteins were as stable to temperature and cell culture conditions as the native protein. Therefore, exchanging the Glu amino acid residue at the amino terminus of onconase with an amino acid residue containing a hydroxyl group produces recombinant proteins with ribonuclease and cytotoxic properties similar to native onconase.

Animals↗
PubMed1998

Toward a universal inhibitor of retroviral proteases: comparative analysis of the interactions of LP-130 complexed with proteases from HIV-1, FIV, and EIAV.

One of the major problems encountered in antiviral therapy against AIDS is the emergence of viral variants that exhibit drug resistance. The sequences of proteases (PRs) from related retroviruses sometimes include, at structurally equivalent positions, amino acids identical to those found in drug-resistant forms of HIV-1 PR. The statine-based inhibitor LP-130 was found to be a universal, nanomolar-range inhibitor against all tested retroviral PRs. We solved the crystal structures of LP-130 in complex with retroviral PRs from HIV-1, feline immunodeficiency virus, and equine infectious anemia virus and compared the structures to determine the differences in the interactions between the inhibitor and the active-site residues of the enzymes. This comparison shows an extraordinary similarity in the binding modes of the inhibitor molecules. The only exceptions are the different conformations of naphthylalanine side chains at the P3/P3' positions, which might be responsible for the variation in the Ki values. These findings indicate that successful inhibition of different retroviral PRs by LP-130 is achieved because this compound can be accommodated without serious conformational differences, despite the variations in the type of residues forming the active-site region. Although strong, specific interactions between the ligand and the enzyme might improve the potency of the inhibitor, the absence of such interactions seems to favor the universality of the compound. Hence, the ability of potential anti-AIDS drugs to inhibit multiple retroviral PRs might indicate their likelihood of not eliciting drug resistance. These studies may also contribute to the development of a small-animal model for preclinical testing of antiviral compounds.

Antiviral Agents↗
PubMed1998

Catalytic triads and their relatives.

Interactions among the residues in the serine protease Asp-His-Ser catalytic triad, in the special environment of the enzyme-substrate complex, activate the nucleophilic potential of the seryl O gamma. In the subtilisin and trypsin families, the composition and arrangement of the catalytic triad do not vary significantly. However, the mechanisms of action of many other hydrolytic enzymes, which target a wide range of substrates, involve nucleophilic attack by a serine (or threonine) residue. Review of these enzymes shows that the acid-base-ser/thr pattern of catalytic residues is generally conserved, although the individual acids and bases can vary. The variations in sequence and organization illustrate the adaptability shown by proteins in generating catalytic stereochemistry on different main-chain frameworks.

Amino Acid Sequence↗
PubMed1998

The structural basis of phage display elucidated by the crystal structure of the N-terminal domains of g3p.

The structure of the two N-terminal domains of the gene 3 protein of filamentous phages (residues 1-217) has been solved by multiwavelength anomalous diffraction and refined at 1.46 A resolution. Each domain consists of either five or eight beta-strands and a single alpha-helix. Despite missing sequence homology, their cores superimposed with a root-mean-square deviation of 2 A. The domains are engaged in extensive interactions, resulting in a horseshoe shape with aliphatic amino acids and threonines lining the inside, delineating the likely binding site for the F-pilus. The glycine-rich linker connecting the domains is invisible in the otherwise highly ordered structure and may confer flexibility between the domains required during the infection process.

Amino Acid Sequence↗
PubMed1998

Inhibitors of HIV-1 protease: a major success of structure-assisted drug design.

Retroviral protease (PR) from the human immunodeficiency virus type 1 (HIV-1) was identified over a decade ago as a potential target for structure-based drug design. This effort was very successful. Four drugs are already approved, and others are undergoing clinical trials. The techniques utilized in this remarkable example of structure-assisted drug design included crystallography, NMR, computational studies, and advanced chemical synthesis. The development of these drugs is discussed in detail. Other approaches to designing HIV-1 PR inhibitors, based on the concepts of symmetry and on the replacement of a water molecule that had been found tetrahedrally coordinated between the enzyme and the inhibitors, are also discussed. The emergence of drug-induced mutations of HIV-1 PR leads to rapid loss of potency of the existing drugs and to the need to continue the development process. The structural basis of drug resistance and the ways of overcoming this phenomenon are mentioned.

Binding Sites↗