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C Humblet

Publications and source records attributed to C Humblet.

At least 37 records · Page 2Linked to original sources
PubMed1996

Binding of tacrine and 6-chlorotacrine by acetylcholinesterase.

Multiconfiguration thermodynamic integration was used to determine the relative binding strength of tacrine and 6-chlorotacrine by Torpedo californica acetylcholinesterase. 6-Chlorotacrine appears to be bound stronger by 0.7+/-0.4 kcal/mol than unsubstituted tacrine when the active site triad residue His-440 is deprotonated. This result is in excellent agreement with experimental inhibition data on electric eel acetylcholinesterase. Electrostatic Poisson-Boltzmann calculations confirm that order of binding strength, resulting in deltaG of binding of -2.9 and -3.3 kcal/mol for tacrine and chlorotacrine, respectively, and suggest inhibitor binding does not occur when His-440 is charged. Our results suggest that electron density redistribution upon tacrine chlorination is mainly responsible for the increased attraction potential between pronated inhibitor molecule and adjacent aromatic groups of Phe-330 and Trp-84.

Acetylcholinesterase↗
PubMed1996

Designing inhibitors of the metalloproteinase superfamily: comparative analysis of representative structures.

Structural comparisons of representative members of the zinc metalloproteinase superfamily show that the key secondary structural elements are conserved, in spite of major variations in the sequences including insertions and deletions of functional domains. Major differences between the matrix metalloproteinases (matrixins) are clustered in two regions forming the entrance to the active site and hence may be determinants of substrate selectivity. A comparison of the structures of matrixin-inhibitor complexes shows that there are significant differences even among the closely related matrixins, not only in the peripheral regions but also in the specificity pockets; these differences offer an excellent opportunity for the design of specific inhibitors targetted to individual members.

Binding Sites↗
PubMed1996

Hydrophobic D-amino acids in the design of peptide ligands for the pp60src SH2 domain.

Src homology-2 (SH2) domains, containing approximately 100 amino acid residues, are noncatalytic motifs involved with intracellular signal transduction. These domains can be found on nonreceptor kinases, phosphatases, and in regulatory adapter proteins among others. SH2 domains bind proteins containing phosphotyrosine (pTyr) residues in a sequence specific manner. Our efforts have focused on designing peptide mimetic ligands for the SH2 domain of the nonreceptor tyrosine kinase pp60src. We employed the cocrystal structure of the 11mer Glu-Pro-Gln-pTyr-Glu-Glu-Ile-Pro-IIe-Tyr-Leu IC50 = 800 nM as a starting point for our design efforts. These efforts have resulted in the discovery of tripeptide ligands containing D-amino acids that are only 2-fold less potent than the 11mer.

Amino Acid Sequence↗
PubMed1996

In vivo expression of interleukin-1 beta (IL-1 beta), IL-2, IL-4, IL-6, tumour necrosis factor-alpha and interferon-gamma in the fetal murine thymus.

Cytokines are known to play a role in T-cell lymphopoiesis as potent growth or differentiation factors, but many experiments focusing on their role in the thymus have been conducted only in vitro. We have thus used frozen sections obtained from fetal thymuses of normal C57BL 6 mice to investigate by immunohistochemistry the presence of interleukin-1 beta (I4-1 beta), IL-2. IL-4. IL-6. interferon-7 (IFN-7) and tumour necrosis facor-alpha (TNF-alpha). The results reveal that apart from IL-2, which was not detected, all these cytokines display a time-dependent expression pattern in the normal fetal thymus. First, production of IL-4, IL-6 and TNF-alpha is detected around days 13 14; this is followed by a second wave on days 16 17, with a production of IL-1 beta, IL-4 and IL-6, and finally, just before birth (day 19), by a third wave of IL-1 beta, IL-4, IL-6, IFN-7 and TNF-alpha production. This supports the hypothesis that cytokines play a rote in T-cell lymphopoiesis.

Animals↗
PubMed1996

Three-dimensional molecular models of the hMC1R melanocortin receptor: complexes with melanotropin peptide agonists.

Three-dimensional molecular models of the human melanocortin receptor (hMC1R) have been developed based upon the electron cryo-microscopic structure of bacteriorhodopsin and the electron density footprint of bovine rhodopsin. alpha-Melanocyte-stimulating hormone, Ac-Ser-Tyr-Ser-Met4-Glu-His-Phe7-Arg-Trp-Gly-Lys-Pro-Val-NH2 (alpha-MSH, alpha-melanotropin), and the superpotent, prolonged acting agonists, Ac-Ser-Tyr-Ser-Nle4-Glu-His-DPhe7-Arg-Trp-Gly-Lys-Pro-Val-NH2 (NDP-MSH) and Ac-Nle4-c[Asp5-His6-DPhe7-Arg8-Trp9-Lys10]-NH2 (MTII), have been modeled into the proposed binding sites with specific ligand-receptor interactions identified. The melanotropin sidechain pharmacophores, DPhe7 and Trp9, are proposed to interact with a hydrophobic network of receptor aromatic residues in transmembrane regions 4, 5, 6, and 7. In addition, a hydrophilic network involving the ligand Arg8 and polar receptor residues located in transmembrane regions 2 and 3 were identified. Biological studies on alpha-MSH, NDP-MSH, MTII, and related peptides have been correlated with the proposed hMC1R model in terms of agonism, affinity, and prolongation. Finally, limited MC1R mutagenesis studies comparing alpha-MSH and NDP-MSH are interpreted within the context of the proposed hMC1R models.

Amino Acid Sequence↗
PubMed1995

Design and synthesis of renin inhibitors: incorporation of transition-state isostere side chains that span from the S1 to the S3 binding pockets and examination of P3-modified renin inhibitors.

A series of renin inhibitors were designed to examine the topography of the contiguous binding pocket of renin that is normally occupied by the P1 and P3 side chains. Molecular modeling suggested that extending the P1 hydrophobic side chain into the adjacent hydrophobic S3 enzyme pocket was feasible. Novel transition state isosteres with modified P1-->P3 side chains were synthesized and provided enhanced binding affinity when incorporated into renin inhibitors in which the P3 Phe was substituted by Gly. In a complementary approach, the binding affinities of a variety of P3-P4-modified peptidomimetic renin inhibitors that lacked substantial hydrophobic side chains at these sites were measured.

Amides↗
PubMed1995

Structural studies on the PH domains of Db1, Sos1, IRS-1, and beta ARK1 and their differential binding to G beta gamma subunits.

Pleckstrin homology (PH) domains are approximately 110 amino acid residues in length and are structurally conserved in a number of intracellular signaling proteins. A role for these domains has been postulated for beta ARK, which binds to G beta gamma subunits. We have quantified the binding of individual (His)6-tag PH domains of human Db1, human Sos1, rat IRS-1, human beta ARK, and human beta ARK with an extra 33-residue C-terminal extension (beta ARK + C) to G beta gamma subunits. Our in vitro binding studies show that all of the PH domains (apart from Sos1), bind G beta gamma subunits in a dose-dependent manner, but beta ARK + C binds 4 times as much G beta gamma at saturation as the others. The IRS-1 PH domain has a similar half-maximal concentration of G beta gamma binding (18 nM) to beta ARK + C (30 nM), suggesting that the IRS-1 PH domain has sufficient determinants for G beta gamma binding. The beta ARK PH domain alone has a half-maximal value of 45 nM but a drastically reduced extent of G beta gamma binding, suggesting that both the PH domain and the C-terminal 33 residues are necessary for maximal binding. Db1 has a half-maximum concentration of G beta gamma binding of 45 nM and a maximal extent of binding similar to that of beta ARK, but it is difficult to demonstrate saturable binding of G beta gamma to Sos1. Since it was previously predicted that the C-terminal PH domain of Pleckstrin [Tyers, M., et al. (1988) Nature 333, 470-473] contains a potential calcium binding site, we have tested the different PH domains for calcium binding. Only the PH domain of Db1 bound 45Ca2+ with a Kd of 10 microM. CD spectroscopy of the purified recombinant PH domains indicated that they are predominantly beta-sheet structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Enhancing the diversity of a corporate database using chemical database clustering and analysis.

The contribution that the Chemical Abstracts structural database (CAST-3D) and the Maybridge database (MAY) would make to diversifying the structural information and property space spanned by our corporate database (CBI) is assessed. A subset of the CAST-3D database has been selected to augment the structural diversity of various electronic databases used in computer-assisted drug design projects. The analysis of the MAY database directly offers the potential to expand the CBI compound library, but also provides a source for structural diversity in a format suitable for computer-assisted database searching and molecular design. The analysis performed is twofold. First, a nonhierarchical clustering technique available in the Daylight clustering package is applied to evaluate the structural differences between databases. The comparison is then extended to analyze various structure-derived property spaces calculated from molecular descriptors such as the logarithm of the octanol-water partition coefficient (CLOGP), the molar refractivity (CMR) and the electronic dipole moment (CDM). The diversity contribution of each database to these property spaces is quantified in relation to our corporate database.

Chemical Phenomena↗
PubMed1995

Morphological changes of thymus in retrovirus-induced murine acquired immunodeficiency syndrome (MAIDS).

The possible contribution of the thymus in the setting of acquired immunodeficiencies is still questioned. Here we report some new findings regarding a potential involvement of the thymus in mice infected with RadLV-Rs, a viral mixture inducing murine acquired immunodeficiency syndrome (MAIDS). Thymi were sequentially removed, weighted and morphologically analyzed at different time intervals post-infection. Infection with RadLV-Rs led to a decrease in thymus weight mostly apparent from the fourth week. The first changes were seen at the third week as perivascular clusters of B-cells at the cortico-medullary junction. The ensuing process of atrophy mainly involved the cortex, while a mixed population of large T- and B-cells filled the medulla. These observations are discussed with regard to the pathological changes occurring in other lymphoid and non-lymphoid organs, in the context of the lymphoproliferation and immunodeficiency characterizing the disease, and by comparison with other models of retrovirus-induced immunodeficiencies.

Animals↗
PubMed1995

Two classes of structurally different antagonists display similar species preference for the human tachykinin neurokinin3 receptor.

Two classes of structurally different tachykinin neurokinin3 (NK3) antagonists were used to evaluate species difference in antagonist binding between human and rat NK3 receptors. In competition binding experiments with [125I-MePhe7]NKB as radioligand, PD 154740, PD 157672, SR 48968, and SR 142801 displayed lower Ki values for the human NK3 receptor (40 +/- 4, 12 +/- 1,350 +/- 50, and 0.40 +/- 0.05 nM, respectively) than for the rat NK3 receptor (2450 +/- 130, 288 +/- 25, > 10,000, and 11.0 +/- 0.5 nM, respectively). Data from in vitro functional assay showed similar species preference as observed with the competition binding assay. It was shown previously that substitution of only two amino acid residues in the rat receptor to their human counterparts could change the species selectivity of SR 48968, a weak NK3 antagonist. In the double-substituted rat mutant, all three antagonists (PD 154740, PD 157672, and SR 142801) displayed Ki values (76 +/- 8, 16 +/- 2, and 0.50 +/- 0.05 nM, respectively) very similar to the Ki values for the wild-type human NK3 receptor. Thus, in addition to their previously reported effects on SR 48968, these two amino acid residues are responsible for the species selectivity of these three additional NK3 antagonists. Because PD 154740 and PD 157672 are very different structurally from SR 48968 and SR 142801, our results indicate that the two identified residues may be involved in adopting a receptor conformation that favors the binding of NK3 antagonists that display species preference for the human NK3 receptor.

Animals↗
PubMed1995

Spontaneous and induced apoptosis after whole body radiation exposure: experimental approaches. Observations in radio-induced thymic lymphomagenesis.

Radio-induced thymic lymphomagenesis is associated with alterations in the balance between thymocyte subsets and cytokinetic perturbations. The objectives of this work were to investigate whether these alterations are associated with alterations in the basic levels of thymocyte apoptosis. For this purpose, we tested DNA fragmentation by gel electrophoresis, analyzed DNA content by propidium iodide staining of ethanol fixed cells and looked for DNA strand breaks on tissue sections by in situ end labeling. We described an increase of the levels of apoptosis in cultured thymocytes during the preleukemic period, while the basic levels of apoptosis observed in situ are similar in normal and in preleukemic thymuses. We propose that after leukemogenic irradiations, there is an increase of cells wherein the cell suicide program is activated but that environmental thymic factors rescue them from apoptosis. Preleukemic cells could belong to this abnormally surviving population of cells "programmed to die," wherein additional genomic abnormalities would lead to fully neoplastic transformation.

Animals↗
PubMed1994

A novel nonpeptide HIV-1 protease inhibitor: elucidation of the binding mode and its application in the design of related analogs.

HIV-1 protease has been identified as a significant target enzyme in AIDS research. While numerous peptide-derived inhibitors have been described, the identification of a nonpeptide inhibitor remains an important goal. Using an HIV-1 protease mass screening technique, 4-hydroxy-3-(3-phenoxypropyl)-2H-1-benzopyran-2-one (1) was identified as a nonpeptide competitive inhibitor of the enzyme. Employing a Monte Carlo-based docking procedure, the coumarin was docked in the active site of the enzyme, revealing a binding mode that was later confirmed by the X-ray crystal analysis. Several analogs were prepared to test the binding interactions and improve the overall binding affinity. The most active compound in the study was 4,7-dihydroxy-3-[4-(2-methoxyphenyl)butyl]-2H-1-benzopyran-2-one (31).

4-Hydroxycoumarins↗
PubMed1994

Analysis by in situ hybridization of cytokine mRNA expression in the murine developing thymus.

We have used in situ hybridization to investigate the expression of IL-1, IL-2, IL-4, IL-6 and IFN-gamma genes by thymic cells during fetal development in mice. Two waves of mRNAs were detected in thymic cells for IL-1 at days 16 and 19 of gestation, for IL-2 at days 14 and 18, and for IL-4 at days 14 and 16. Three peaks for IL-6 were observed at days 13, 17 and around birth. Finally, only one peak of cells positive for IFN-gamma was detected. Whereas cells positive for IL-1 were generally grouped and more often localized in the external area of the thymus, the other positive cells were isolated and evenly distributed in the thymus. Our results illustrated the presence of cytokine transcripts in the developing thymus following a developmentally controlled sequence and support the hypothesis that cytokines could play a role in T cell development.

Animals↗
PubMed1994

Presentation and intercellular transfer of self antigen within the thymic microenvironment: expression of the E alpha peptide-I-Ab complex by isolated thymic stromal cells.

Expression of a self peptide derived from the alpha chain of MHC class II (I-Ed) in association with I-Ab was studied in the murine thymic microenvironment. Previous work using the mAb Y-Ae which specifically recognizes the E alpha-I-Ab complex had reported differential expression between the thymic medulla and the cortex of this peptide-MHC complex: MHC class II-positive stromal cells in the medulla were strongly positive, whereas this complex was barely detectable on cortical epithelial cells (cEpC) in situ. This difference in presentation of an abundant self peptide is intriguing, since the self protein from which this peptide is derived and the presenting MHC molecule are strongly expressed in both compartments. In this report we show by cell surface phenotype and functional assays that isolated cEpC express the E alpha-I-Ab complex at significant although lower levels than medullary dendritic cells (DC), when examined ex vivo. These results support the notion that cEpC and bone marrow-derived stromal cells present a similar set of self peptide-MHC complexes in situ. In addition, we detect intercellular transfer in situ of the E alpha determinant from radioresistant stromal cells to thymic DC, a mechanism which may enhance the efficacy of tolerance induction by spreading self antigens with the thymic microenvironment.

Animals↗
PubMed1994

Thymus involvement in murine acquired immunodeficiency (MAIDS).

Due to self-renewal of the peripheral pool of T-cells, adult thymectomy has normally little influence on immunocompetence. However, thymus might play a more important role in the setting of viral-induced cytopathic effects on T-cells in the periphery. Therefore, thymus weight, cell numbers, and subset distribution were sequentially analysed after infection with RadLV-Rs, a viral mixture known to induce murine retrovirus induced immunodeficiency (MAIDS). Infection induced thymic atrophy (concerning organ weight as well as total cell number) which culminated seven weeks after inoculation. The atrophic process mostly reflected the depletion of double positive CD4+ CD8+ cells since their proportion sharply decreased around week 6. Single positive T-cells were less affected by the process. The proportion of B-cells progressively increased. Surprisingly, there was a strong correlation between the extent of atrophy and the frequency of B-cells in the thymus. Finally, an abnormal CD4+ T-cell subset lacking Thy-1 and previously described in the periphery also appeared in the thymus and its frequency was strongly correlated with the expansion of B-cells in this organ.

Animals↗