Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

1-POS Board 1 Vinculin and Its Fundamental Role in Actin Bundling Formation Ernesto Alva Sevilla 2,1 , Andrey Krokhotin 1 , Nikolay V. Dokholyan 1 . 2 University of Texas at San Antonio, San Antonio, TX, USA. 1 University of North Carolina at Chapel Hill, Chapel Hill, NC, USA, Vinculin is an abundant and essential cytoskeletal protein that localizes to focal adhesions and adherent junctions. The interaction between vinculin and actin plays a pivotal role in linking transmembrane receptors to the cytoskeleton, which in turn, is important for controlling cellular force transmission, cell morphology and motility. Vinculin binds to F-actin and undergoes a conformational change that induces formation of a cryptic dimer necessary for actin filament bundling, but nature of the dimer formed remains unknown. Here, we employ computational approaches, including discrete molecular dynamic simulations, to investigate actin-induced conformational changes in the vinculin tail (Vt) domain that facilitate dimer formation and actin bundling. We find that actin engagement with Vt alters both the N-terminal helix (H1) and C- terminus of Vt, and that conformational changes within the N- and C-terminus are necessary for the formation of stable interfaces with the actin surface. We argue that this interface is important for Vt dimerization. We show that residue deletions with the C-terminus (∆CT1, ∆CT2, and ∆CT5) affect the stability of this interface, consistent with previously published experimental findings that C-terminal deletions within Vt reduce actin bundling activity. These observations are supported by additional mutagenesis data. Intriguingly, we find that the presence of tryptophan at position 912 destabilizes H1 helix and postulate that instability introduced by W912 plays an important role allowing H1 to unfold upon actin association. Experiments are in progress to test our actin-induced vinculin dimer model and examine the role of this W912 in vinculin-mediated actin bundling.

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