January 2010

For Talin, It’s Avidity Not Affinity

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PAC-1 IgM binding to CHO cells is clustered.

The protein talin can bind to the cytoplasmic tail regions of β3 integrins and regulate the activity of αIIbβ3 integrins. Talin itself is autoregulated – its integrin-binding globular head region can be inhibited by binding to the talin C-terminal tail. Interestingly, while overexpression of the talin head domain increases integrin activity in mammalian cells, such effects are not seen in Drosophila, suggesting talin-integrin interactions may be different in those organisms. However, in this paper, the author shows that the discrepancies are due to differences in methodologies. Using a Drosophila-based assay that employs only monovalent ligands (where one ligand binds to one integrin receptor), the author found that talin had no effect on the affinity of αIIbβ3 integrins for ligand in Chinese hamster ovary (CHO) cells or human platelets. Talin did increase the ability of integrins to bind to multivalent ligands that can interact with more than one receptor, but this was due to increased integrin clustering and not affinity. This study helps reconcile the experimental differences and also suggests a new model by which talin regulates integrin activity.

Integrin αIIbβ3 Activation in CHO Cells and Platelets Increases Clustering not Affinity

Thomas A. Bunch

J. Biol. Chem., published online Nov. 16, 2009 

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