Biomedical subjects

K Decanniere

Publications and source records attributed to K Decanniere.

10 recordsLinked to original sources

PubMed2001

Degenerate interfaces in antigen-antibody complexes.

In most of the work dealing with the analysis of protein-protein interfaces, a single X-ray structure is available or selected, and implicitly it is assumed that this structure corresponds to the optimal complex for this pair of proteins. However, we have found a degenerate interface in a high-affinity antibody-antigen complex: the two independent complexes of the camel variable domain antibody fragment cAb-Lys3 and its antigen hen egg white lysozyme present in the asymmetric unit of our crystals show a difference in relative orientation between antibody and antigen, leading to important differences at the protein-protein interface. A third cAb-Lys3-hen lysozyme complex in a different crystal form adopts yet another relative orientation. Our results show that protein-protein interface characteristics can vary significantly between different specimens of the same high-affinity antibody-protein antigen complex. Consideration should be given to this type of observation when trying to establish general protein-protein interface characteristics.

Animals↗

PubMed2001

Antigen specificity and high affinity binding provided by one single loop of a camel single-domain antibody.

Detailed knowledge on antibody-antigen recognition is scarce given the unlimited antibody specificities of which only few have been investigated at an atomic level. We report the crystal structures of an antibody fragment derived from a camel heavy chain antibody against carbonic anhydrase, free and in complex with antigen. Surprisingly, this single-domain antibody interacts with nanomolar affinity with the antigen through its third hypervariable loop (19 amino acids long), providing a flat interacting surface of 620 A(2). For the first time, a single-domain antibody is observed with its first hypervariable loop adopting a type-1 canonical structure. The second hypervariable loop, of unique size due to a somatic mutation, reveals a regular beta-turn. The third hypervariable loop covers the remaining hypervariable loops and the side of the domain that normally interacts with the variable domain of the light chain. Specific amino acid substitutions and reoriented side chains reshape this side of the domain and increase its hydrophilicity. Of interest is the substitution of the conserved Trp-103 by Arg because it opens new perspectives to 'humanize' a camel variable domain of heavy chain of heavy chain antibody (VHH) or to 'camelize' a human or a mouse variable domain of heavy chain of conventional antibody (VH).

Amino Acid Sequence↗

PubMed2001

Structure and function of a novel purine specific nucleoside hydrolase from Trypanosoma vivax.

The purine salvage pathway of parasitic protozoa is currently considered as a target for drug development because these organisms cannot synthesize purines de novo. Insight into the structure and mechanism of the involved enzymes can aid in the development of potent inhibitors, leading to new curative drugs. Nucleoside hydrolases are key enzymes in the purine salvage pathway of Trypanosomatidae, and they are especially attractive because they have no equivalent in mammalian cells. We cloned, expressed and purified a nucleoside hydrolase from Trypanosoma vivax. The substrate activity profile establishes the enzyme to be a member of the inosine-adenosine-guanosine-preferring nucleoside hydrolases (IAG-NH). We solved the crystal structure of the enzyme at 1.6 A resolution using MAD techniques. The complex of the enzyme with the substrate analogue 3-deaza-adenosine is presented. These are the first structures of an IAG-NH reported in the literature. The T. vivax IAG-NH is a homodimer, with each subunit consisting of ten beta-strands, 12 alpha-helices and three small 3(10)-helices. Six of the eight strands of the central beta-sheet form a motif resembling the Rossmann fold. Superposition of the active sites of this IAG-NH and the inosine-uridine-preferring nucleoside hydrolase (IU-NH) of Crithidia fasciculata shows the molecular basis of the different substrate specificity distinguishing these two classes of nucleoside hydrolases. An "aromatic stacking network" in the active site of the IAG-NH, absent from the IU-NH, imposes the purine specificity. Asp10 is the proposed general base in the reaction mechanism, abstracting a proton from a nucleophilic water molecule. Asp40 (replaced by Asn39 in the IU-NH) is positioned appropriately to act as a general acid and to protonate the purine leaving group. The second general acid, needed for full enzymatic activity, is probably part of a flexible loop located in the vicinity of the active site.

Amino Acid Sequence↗

PubMed2000

Crystal structures of recombinant histones HMfA and HMfB from the hyperthermophilic archaeon Methanothermus fervidus.

The hyperthermophilic archaeon Methanothermus fervidus contains two small basic proteins, HMfA (68 amino acid residues) and HMfB (69 residues) that share a common ancestry with the eukaryal nucleosome core histones H2A, H2B, H3, and H4. HMfA and HMfB have sequences that differ at 11 locations, they have different structural stabilities, and the complexes that they form with DNA have different electrophoretic mobilities. Here, crystal structures are documented for recombinant (r) HMfA at a resolution of 1.55 A refined to a crystallographic R-value of 19.8 % (tetragonal form) and at 1.48 A refined to a R-value of 18.8 % (orthorhombic form), and for rHMfB at 1.9 A refined to a R-value of 18.0 %. The rHMfA and rHMfB monomers have structures that are just histone folds in which a long central alpha-helix (alpha2; 29 residues) is separated from shorter N-terminal (alpha1; 11 residues) and C-terminal (alpha3; 10 residues) alpha-helices by two loops (L1 and L2; both 6 residues). Within L1 and L2, three adjacent residues are in extended (beta) conformation. rHMfA and rHMfB assemble into homodimers, with the alpha2 helices anti-parallel aligned and crossing at an angle of close to 35 degrees, and with hydrogen bonds formed between the extended, parallel regions of L1 and L2 resulting in short beta-ladders. Dimerization creates a novel N-terminal structure that contains four proline residues, two from each monomer. As prolines are present at these positions in all archaeal histone sequences, this proline-tetrad structure is likely to be a common feature of all archaeal histone dimers. Almost all residues that participate in monomer-monomer interactions are conserved in HMfA and HMfB, consistent with the ability of these monomers to form both homodimers and (HMfA+HMfB) heterodimers. Differences in side-chain interactions that result from non-conservative residue differences in HMfA and HMfB are identified, and the structure of a (rHMfA)(2)-DNA complex is presented based on the structures documented here and modeled by homology to histone-DNA interactions in the eukaryal nucleosome.

Amino Acid Sequence↗

PubMed2000

Canonical antigen-binding loop structures in immunoglobulins: more structures, more canonical classes?

Grafting the antigen-binding loops onto a human antibody scaffold is a widely used technique to humanise murine antibodies. The success of this approach depends largely on the observation that the antigen-binding loops adopt only a limited number of canonical structures. Identification of the correct canonical structure is therefore essential. Algorithms that predict the main-chain conformation of the hypervariable loops using only the amino acid sequence often provide this information. Here, we describe new canonical loop conformations for the hypervariable regions H1 and H2 as found in single-domain antibody fragments of dromedaries or llama. Although the occurrence of these new loop conformations was not predicted by the algorithms used, it seems that they could occur in human or mouse antigen-binding loops. Their discovery indicates that the currently used set of canonical structures is incomplete and that the prediction algorithms should be extended to include these new structures.

Algorithms↗

PubMed1999

Conserved water molecules in a large family of microbial ribonucleases.

We systematically analyzed the crystallographically determined water molecules of all known structures of RNase T1 and compared them to the ordered solvent in a large number of related microbial nucleases. To assess the crystallographers' impact on the interpretation of the solvent structure, we independently refined five validation structures from diffraction data derived from five isomorphous crystals of RNase T1. We also compared the positions of water molecules found in 11 published isomorphous RNase T1 inhibitor complexes. These data suggest that the positions of most of the waters located on the surface of a protein and that are well-determined in the experimental electron density maps are determined primarily by crystal packing forces. Water molecules with less well-defined electron density are in general unique to one or a small number of crystal structures. Only a small number of the well-defined waters are found to be independent of the crystal environment. These waters have a low accessible surface area and B-factor, and tend to be conserved in the crystal structures of a number of evolutionary related ribonucleases as well. A single water molecule is found conserved in all known microbial ribonucleases.

Amino Acid Sequence↗

PubMed1999

A single-domain antibody fragment in complex with RNase A: non-canonical loop structures and nanomolar affinity using two CDR loops.

BACKGROUND: Camelid serum contains a large fraction of functional heavy-chain antibodies - homodimers of heavy chains without light chains. The variable domains of these heavy-chain antibodies (VHH) have a long complementarity determining region 3 (CDR3) loop that compensates for the absence of the antigen-binding loops of the variable light chains (VL). In the case of the VHH fragment cAb-Lys3, part of the 24 amino acid long CDR3 loop protrudes from the antigen-binding surface and inserts into the active-site cleft of its antigen, rendering cAb-Lys3 a competitive enzyme inhibitor. RESULTS: A dromedary VHH with specificity for bovine RNase A, cAb-RN05, has a short CDR3 loop of 12 amino acids and is not a competitive enzyme inhibitor. The structure of the cAb-RN05-RNase A complex has been solved at 2.8 A. The VHH scaffold architecture is close to that of a human VH (variable heavy chain). The structure of the antigen-binding hypervariable 1 loop (H1) of both cAb-RN05 and cAb-Lys3 differ from the known canonical structures; in addition these H1 loops resemble each other. The CDR3 provides an antigen-binding surface and shields the face of the domain that interacts with VL in conventional antibodies. CONCLUSIONS: VHHs adopt the common immunoglobulin fold of variable domains, but the antigen-binding loops deviate from the predicted canonical structure. We define a new canonical structure for the H1 loop of immunoglobulins, with cAb-RN05 and cAb-Lys3 as reference structures. This new loop structure might also occur in human or mouse VH domains. Surprisingly, only two loops are involved in antigen recognition; the CDR2 does not participate. Nevertheless, the antigen binding occurs with nanomolar affinities because of a preferential usage of mainchain atoms for antigen interaction.

Amino Acid Sequence↗

PubMed1999

Crystallization and preliminary x-ray diffraction analysis of hydroxynitrile lyase from cassava (Manihot esculenta).

Hydroxynitrile lyase from M. esculenta (cassava) was crystallized in two different crystal forms by the hanging-drop vapour-diffusion method. Crystals of form I were obtained from a mixture of polyethylene glycol 8000 and 2-methyl-2,4-pentanediol, and belong to the tetragonal space group P41212 or its enantiomorph P43212, with unit-cell parameters a = b = 105.9, c = 188.9 A and with two molecules in the asymmetric unit. These crystals diffract to 2.9 A with conventional X-ray sources and beyond 2.1 A resolution with synchrotron radiation. The crystals are relatively sensitive to radiation damage and conditions for flash-cooling the crystals have been established. A complete native data set has been collected up to 2.2 A resolution. Crystal form II has been obtained at pH 5.6 using lithium sulfate as a precipitant. The crystals apparently belong to the orthorhombic space group P21212, with unit-cell parameters a = 117.52, b = 127.09 and c = 78.08 A, have two molecules in the asymmetric unit and diffract to beyond 2.0 A resolution. A complete native data set has been collected to 2.2 A resolution.

Aldehyde-Lyases↗

PubMed1998

Crystal structures and properties of de novo circularly permuted 1,3-1,4-beta-glucanases.

The 1,3-1,4-beta-glucanases from Bacillus macerans and Bacillus licheniformis, as well as related hybrid enzymes, are stable proteins comprised of one compact jellyroll domain. Their structures are studied in an effort to reveal the degree of redundancy to which the three-dimensional structure of protein domains is encoded by the amino acid sequence. For the hybrid 1,3-1,4-beta-glucanase H(A16-M), it could be shown recently that a circular permutation of the sequence giving rise to the variant cpA16M-59 is compatible with wildtype-like enzymatic activity and tertiary structure (Hahn et al., Proc. Natl. Acad. Sci. USA 91:10417-10421, 1994). Since the circular permutation yielding cpA16M-59 mimicks that found in the homologous enzyme from Fibrobacter succinogenes, the question arose whether de novo circular permutations, not guided by molecular evolution of the 1,3-1,4-beta-glucanases, could also produce proteins with native-like fold. The circularly permuted variants cpA16M-84, cpA16M-127, and cpA16M-154 were generated by PCR mutagenesis of the gene encoding H(A16-M), synthesized in Escherichia coli and shown to be active in beta-glucan hydrolysis. CpA16M-84 and cpA16M-127 were crystallized in space groups P2(1) and P1, respectively, and their crystal structures were determined at 1.80 and 2.07 A resolution. In both proteins the main parts of the beta-sheet structure remain unaffected by the circular permutation as is evident from a root-mean-square deviation of main chain atoms from the reference structure within the experimental error. The only major structural perturbation occurs near the novel chain termini in a surface loop of cpA16M-84, which becomes destabilized and rearranged. The results of this study are interpreted to show that: (1) several circular permutations in the compact jellyroll domain of the 1,3-1,4-beta-glucanases are tolerated without radical change of enzymatic activity or tertiary structure, (2) the three-dimensional structures of simple domains are encoded by the amino acid sequence with sufficient redundancy to tolerate a change in the sequential order of secondary structure elements along the sequence, and (3) the native N-terminal region is not needed to guide the folding polypeptide chain toward its native conformation.

Amino Acid Sequence↗

PubMed1996

Crystallization and preliminary X-ray characterization of the Methanothermus fervidus histones HMfA and HMfB.

HMfA and HMfB are histone proteins from the thermophilic archaeon Methanothermus fervidus. They wrap DNA into nucleosome-like structures and appear to represent the basic core histone fold. HMfA was crystallized in space groups P4(2)2(1)2 and P2(1)2(1)2(1). HMfB crystallized in space group P2(1)2(1)2, while a selenomethionine-substituted variant, SeMet-HMfB, yielded crystals in C222(1). In all crystal forms HMfA, HMfB, or SeMet-HMfB may be present as homodimers.

Bacterial Proteins↗