In silico
 mapping of allosteric ligand binding sites in type-1 cannabinoid receptor

Necator americanus fatty acid and retinol-binding protein-1 (Na-FAR-1) is an abundantly expressed FAR from a parasitic hookworm. The present work describes its tissue distribution, structure and ligand-binding characteristics and shows that Na-FAR-1 expands to transport multiple FA molecules in its internal cavity.

Download Full-text

Adenosine Receptors of Cerebral Microvessels and Choroid Plexus

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1986.80 ◽

1986 ◽

Vol 6 (4) ◽

pp. 463-470 ◽

Cited By ~ 33

Author(s):

Rajesh N. Kalaria ◽

Sami I. Harik

Keyword(s):

Cerebral Cortex ◽

Ligand Binding ◽

Choroid Plexus ◽

Adenosine Receptors ◽

Binding Sites ◽

Specific Binding ◽

Cerebral Microvessels ◽

High Affinity ◽

Receptor Sites ◽

Ligand Binding Sites

We studied, by ligand binding methods, the two adenosine receptors, A, and A2, in rat and pig cerebral microvessels and pig choroid plexus. Ligand binding to cerebral microvessels was compared with that to membranes of the cerebral cortex. [3H]Cyclohexyladenosine and [3H]l-phenylisopropyladenosine were the ligands used for A1-receptors, and [3H]5'- N-ethylcarboxamide adenosine ([3H]NECA) was used to assess A2-receptors. We report that cerebral microvessels and choroid plexus exhibit specific [3H]NECA binding, but have no appreciable A1-receptor ligand binding sites. Specific binding of [3H]NECA to cerebral microvessels, choroid plexus, and cerebral cortex was saturable and suggested the existence of two classes of A2-receptor sites: high-affinity ( Kd ∼ 250 n M) and low-affinity ( Kd ∼ 1–2 μ M) sites. The Kd and Bmax of NECA binding to cerebral microvessels and cerebral cortex were similar within each species. Our results, indicating the existence of A2-receptors in cerebral microvessels, are consistent with results of increased adenylate cyclase activity by adenosine and some of its analogues in these microvessels.

Download Full-text

A naturally occurring Tyr143HisαIIb mutation abolishes αIIbβ3 function for soluble ligands but retains its ability for mediating cell adhesion and clot retraction: comparison with other mutations causing ligand-binding defects

Blood ◽

10.1182/blood-2002-07-2144 ◽

2003 ◽

Vol 101 (9) ◽

pp. 3485-3491 ◽

Cited By ~ 17

Author(s):

Teruo Kiyoi ◽

Yoshiaki Tomiyama ◽

Shigenori Honda ◽

Seiji Tadokoro ◽

Morio Arai ◽

...

Keyword(s):

Cell Adhesion ◽

Ligand Binding ◽

Binding Sites ◽

Clot Retraction ◽

Naturally Occurring ◽

Binding Function ◽

293 Cells ◽

Ligand Binding Sites ◽

Functional Defect ◽

And Function

The molecular basis for the interaction between a prototypic non–I-domain integrin, αIIbβ3, and its ligands remains to be determined. In this study, we have characterized a novel missense mutation (Tyr143His) in αIIb associated with a variant of Glanzmann thrombasthenia. Osaka-12 platelets expressed a substantial amount of αIIbβ3(36%-41% of control) but failed to bind soluble ligands, including a high-affinity αIIbβ3-specific peptidomimetic antagonist. Sequence analysis revealed that Osaka-12 is a compound heterozygote for a single 521T>C substitution leading to a Tyr143His substitution in αIIb and for the null expression of αIIb mRNA from the maternal allele. Given that Tyr143 is located in the W3 4-1 loop of the β-propeller domain of αIIb, we examined the effects of Tyr143His or Tyr143Ala substitution on the expression and function of αIIbβ3 and compared them with KO (Arg-Thr insertion between 160 and 161 residues of αIIb) and with the Asp163Ala mutation located in the same loop by using 293 cells. Each of them abolished the binding function of αIIbβ3 for soluble ligands without disturbing αIIbβ3 expression. Because immobilized fibrinogen and fibrin are higher affinity/avidity ligands for αIIbβ3, we performed cell adhesion and clot retraction assays. In sharp contrast to KO mutation and Asp163AlaαIIbβ3, Tyr143HisαIIbβ3-expressing cells still had some ability for cell adhesion and clot retraction. Thus, the functional defect induced by Tyr143HisαIIb is likely caused by its allosteric effect rather than by a defect in the ligand-binding site itself. These detailed structure–function analyses provide better understanding of the ligand-binding sites in integrins.

Download Full-text