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Biomedical subjects

M H le Du

Publications and source records attributed to M H le Du.

5 recordsLinked to original sources
PubMed2000

Observation of an unexpected third receptor molecule in the crystal structure of human interferon-gamma receptor complex.

BACKGROUND: Molecular interactions among cytokines and cytokine receptors form the basis of many cell-signaling pathways relevant to immune function. Interferon-gamma (IFN-gamma) signals through a multimeric receptor complex consisting of two different but structurally related transmembrane chains: the high-affinity receptor-binding subunit (IFN-gammaRalpha) and a species-specific accessory factor (AF-1 or IFN-gammaRbeta). In the signaling complex, the two receptors probably interact with one another through their extracellular domains. Understanding the atomic interactions of signaling complexes enhances the ability to control and alter cell signaling and also provides a greater understanding of basic biochemical processes. RESULTS: The crystal structure of the complex of human IFN-gamma with the soluble, glycosylated extracellular part of IFN-gammaRalpha has been determined at 2.9 A resolution using multiwavelength anomalous diffraction methods. In addition to the expected 2:1 complex, the crystal structure reveals the presence of a third receptor molecule not directly associated with the IFN-gamma dimer. Two distinct intermolecular contacts, involving the edge strands of the C-terminal domains, are observed between this extra receptor and the 2:1 receptor-ligand complex thereby forming a 3:1 complex. CONCLUSIONS: The observed interactions in the 2:1 complex of the high-affinity cell-surface receptor with the IFN-gamma cytokine are similar to those seen in a previously reported structure where the receptor chains were not glycosylated. The formation of beta-sheet packing interactions between pairs of IFN-gammaRalpha receptors in these crystals suggests a possible model for receptor oligomerization of Ralpha and the structurally homologous Rbeta receptors in the fully active IFN-gamma signaling complex.

Binding Sites↗
PubMed2000

Do structural deviations between toxins adopting the same fold reflect functional differences?

Three-finger proteins form a structurally related family of compounds that exhibit a great variety of biological properties. To address the question of the prediction of functional areas on their surfaces, we tentatively conferred the acetylcholinesterase inhibitory activity of fasciculins on a short-chain curaremimetic toxin. For this purpose, we assimilated the three-dimensional structure of fasciculin 2 with the one of toxin alpha. This comparison revealed that the tips of the first and second loops, together with the C terminus residue, deviated most. A first recombinant fasciculin/toxin alpha chimera was designed by transferring loop 1 in its entirety together with the tip of loop 2 of fasciculin 2 into the toxin alpha scaffold. A second chimera (rChII) was obtained by adding the point Asn-61 --> Tyr substitution. Comparison of functional and structural properties of both chimeras show that rChII can accommodate the imposed modifications and displays nearly all the acetylcholinesterase-blocking activities of fasciculins. The three-dimensional structure of rChII demonstrates that rChII adopts a typical three-fingered fold with structural features of both parent toxins. Taken together, these results emphasize the great structural flexibility and functional adaptability of that fold and confirm that structural deviations between fasciculins and short-chain neurotoxins do indeed reflect functional diversity.

Amino Acid Sequence↗
PubMed1994

Crystal structure of ribonuclease A.d(ApTpApApG) complex. Direct evidence for extended substrate recognition.

The crystal structure of the complex between ribonuclease A and d(ApTpApApG) has been solved by x-ray crystallography using the molecular replacement method. The model includes, besides the enzyme, the d(ApTpApA) 5'-segment (A1T2A3A4) and 68 solvent molecules. The R-factor for the strongest 87% of the measured data that partially extends to 2.3-A resolution is 0.207. The A1 position is well defined; the 5'-O of the deoxyribose establishes a hydrogen bond with a solvent molecule that is, in turn, bonded to the epsilon-amino group of Lys66. The base (B0 site) is well ordered; it interacts with a symmetry-related enzyme molecule. In the crystal, the phosphate group at the p0 site has no direct charge compensation. However, Lys66 is not too far, and, in solution, it could bind to it. The T2 (R1B1p1) site is occupied as in other complex structures, and it is defined by very good electron density. The A3 site shows that the adenine moiety interacts with Asn71 and Gln69 and that the phosphate at p2 forms a salt bridge with Lys7. The most consistent model for the base of A4 (B3), both in terms of electron density and stereochemistry, shows that it forms a hydrogen bond with Gln69 and a g-g- array with the base at B2. The stacking of B2 and B3 may be a general feature of the binding of polyribonucleotides to ribonuclease A. The side chains of Gln69, Asn71, and Glu111 may thus constitute a malleable binding site capable of establishing various hydrogen bonds depending on the nature of the stacked bases. There is no evidence for the 3' G5 site in the electron density map.

Crystallography, X-Ray↗
PubMed1992

1.9-A resolution structure of fasciculin 1, an anti-acetylcholinesterase toxin from green mamba snake venom.

The crystal structure of fasciculin 1, a potent acetylcholinesterase inhibitor from green mamba snake venom, has been solved by the multiple isomorphous replacement method complemented with anomalous scattering and subsequently refined at 1.9-A resolution. The overall structure of fasciculin is similar to those of the short alpha-neurotoxins and cardiotoxins, with a dense core rich in disulfide bridges and three long loops disposed as the central fingers of a hand. A comparison of these three prototypic toxin types shows that fasciculin 1 has structural features that are intermediate between those of the other two molecules. Its core region, which can be defined as a continuous stretch of conserved residues, is very similar to that of erabutoxin b, whereas the orientation of its long loops resembles that of cardiotoxin VII4. This result introduces a new element in the study of phylogenetic relationships of snake toxins and suggests that, after divergency from an ancestral gene, convergent evolution may have played an important factor in the evolution of these proteins. In fasciculin 1, several arginine and lysine residues are well ordered and relatively exposed to the solvent medium and may play a role in the binding to the peripheral site of acetylcholinesterases.

Amino Acid Sequence↗