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Small Ligands (small + ligand)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

A Val193Met mutation in GPIIIa results in a GPIIb/IIIa receptor with a constitutively high affinity for a small ligand

BRITISH JOURNAL OF HAEMATOLOGY, Issue 1 2001
John Fullard
We have identified a patient designated as (GTa) with Glanzmann's Thrombasthenia (GT) diagnosed on the basis of a prolonged bleeding time and failure of the patient's platelets to aggregate. The number of glycoprotein (GP)IIb/IIIa receptors on the platelet surface was 37% of normal and those receptors displayed a defect in soluble fibrinogen binding. Nevertheless, GTa platelets showed increased adhesion to solid-phase fibrinogen and binding affinity for the RGD-mimetic 3H-SC52012, a non-peptide GPIIb/IIIa antagonist. Dithiothreitol (DTT) and ADP enhanced the affinity for [3H]-SC52012 in normal platelets, but had little effect in GTa platelets. These findings suggested that GTa platelets were locked in an altered affinity state. Genetic analysis showed that GTa was a compound heterozygote for the GPIIIa gene. One allele showed a deletion at the 3, end of exon 3 resulting in a premature stop codon. The second GPIIIa allele had a G to A transition at nucleotide 577, resulting in a Val193Met substitution. HEK 293T cells transfected with mutant GPIIb/IIIaV193M bound [3H]-SC52012 with a higher affinity than wild-type GPIIb/IIIa, and this was not increased by DTT. The mutant receptor distinguishes between platelet adhesion and aggregation, and demonstrates the phenotype that may be expected when platelet aggregation alone is inhibited. [source]

Coordination chemistry of iron(III),porphyrin,antibody complexes

FEBS JOURNAL, Issue 2 2002
Influence on the peroxidase activity of the axial coordination of an imidazole on the iron atom
An artificial peroxidase-like hemoprotein has been obtained by associating a monoclonal antibody, 13G10, and its iron(III),,,,,,,,- meso -tetrakis(ortho -carboxyphenyl)porphyrin [Fe(ToCPP)] hapten. In this antibody, about two-thirds of the porphyrin moiety is inserted in the binding site, its ortho -COOH substituents being recognized by amino-acids of the protein, and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O,O bond of H2O2, but no amino-acid residue is acting as an axial ligand of the iron. We here show that the iron of 13G10,Fe(ToCPP) is able to bind, like that of free Fe(ToCPP), two small ligands such as CN,, but only one imidazole ligand, in contrast to to the iron(III) of,Fe(ToCPP) that binds two. This phenomenon is general for a series of monosubstituted imidazoles, the 2- and 4-alkyl-substituted imidazoles being the best ligands, in agreement with the hydrophobic character of the antibody binding site. Complexes of antibody 13G10 with less hindered iron(III),tetraarylporphyrins bearing only one [Fe(MoCPP)] or two meso-[ortho -carboxyphenyl] substituents [Fe(DoCPP)] also bind only one imidazole. Finally, peroxidase activity studies show that imidazole inhibits the peroxidase activity of 13G10,Fe(ToCPP) whereas it increases that of 13G10,Fe(DoCPP). This could be interpreted by the binding of the imidazole ligand on the iron atom which probably occurs in the case of 13G10,Fe(ToCPP) on the less hindered face of the porphyrin, close to the catalytic COOH residue, whereas in the case of 13G10,Fe(DoCPP) it can occur on the other face of the porphyrin. The 13G10,Fe(DoCPP),imidazole complex thus constitutes a nice artificial peroxidase-like hemoprotein, with the axial imidazole ligand of the iron mimicking the proximal histidine of peroxidases and a COOH side chain of the antibody acting as a general acid-base catalyst like the distal histidine of peroxidases does. [source]

Combined use of nuclear magnetic resonance and infrared spectroscopy for studying recognition processes between amphenicolic antibiotics and albumin

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003
Silvia Martini
Abstract Biological reactions are mostly concerned with selective interactions between small ligands and macromolecular receptors. The same ligands may activate responses of different intensities and/or effects in the presence of different receptors. Many approaches based on spectroscopic and non-spectroscopic methods have been used to study interactions between small ligands and macromolecular receptors, including methods based on NMR and IR spectroscopic analysis of the solution behaviour of the ligand in the presence of receptors. In this work, we investigated the interaction between ovine serum albumin with two amphenicolic antibiotics [chloramphenicol (CAP) and thiamphenicol (TAP)], using a combined approach based on NMR and IR methodologies, furnishing complementary information about the recognition process occurring within the two systems. The two ligands, despite their similar structures, showed different affinities towards albumin. NMR methodology is based on the comparison of selective () and non-selective () spin,lattice relaxation rates of the ligands in the presence and absence of macromolecular receptors and and temperature dependence analysis. From these studies, the ligand,receptor binding strength was evaluated on the basis of the ,affinity index.' The derivation of the affinity index from chemical equilibrium kinetics for both the CAP,albumin and TAP,albumin systems allowed a comparison of the abilities of the two amphenicolic antibiotics to interact with the protein. IR methodology is based on the comparison of the ligand,protein ,complex' spectra with those of the non-interacting systems. On the basis of the differences revealed, a more thorough IR analysis was performed in order to understand the structural changes which occurred on both ligand and protein molecules within the interacting system. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Cloning, overexpression, purification, crystallization and preliminary X-ray analysis of a female-specific lipocalin (FLP) expressed in the lacrimal glands of Syrian hamsters

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2010
Ved Prakash Dubey
Proteins belonging to the lipocalin superfamily are usually secretory proteins of molecular mass ,20,kDa with a hydrophobic pocket for the binding and transport of diverse small ligands. Various lipocalins have been associated with many biological processes, e.g. immunomodulation, odorant transport, pheromonal activity, retinoid transport, cancer-cell interactions etc. However, the exact functions of many lipocalins and the ligands bound by them are unclear. Previously, the cDNA of a 20,kDa lipocalin (FLP) which is female-specifically expressed in the lacrimal glands of Syrian (golden) hamsters and secreted in the tears of females has been identified and cloned. His-tagged recombinant FLP (rFLP) has now been cloned, overexpressed in Escherichia coli as a soluble protein and purified to homogeneity using Ni-affinity followed by size-exclusion chromatography. Purified rFLP was crystallized using the sitting-drop vapour-diffusion method. The crystals tested belonged to space group P212121 and diffracted to beyond 1.86,Å resolution. Solvent-content analysis indicated the presence of one monomer in the asymmetric unit. [source]

Solution structure of Arabidopsis thaliana protein At5g39720.1, a member of the AIG2-like protein family

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2006
Betsy L. Lytle
The three-dimensional structure of Arabidopsis thaliana protein At5g39720.1 was determined by NMR spectroscopy. It is the first representative structure of Pfam family PF06094, which contains protein sequences similar to that of AIG2, an A. thaliana protein of unknown function induced upon infection by the bacterial pathogen Pseudomonas syringae. The At5g39720.1 structure consists of a five-stranded ,-barrel surrounded by two ,-helices and a small ,-sheet. A long flexible ,-helix protrudes from the structure at the C-terminal end. A structural homology search revealed similarity to three members of Pfam family UPF0131. Conservation of residues in a hydrophilic cavity able to bind small ligands in UPF0131 proteins suggests that this may also serve as an active site in AIG2-like proteins. [source]