Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Poster Abstracts

20-POS Board 20 Visualization of Structural Changes Accompanying Activation of Kainate Receptors Using Fast-Scan Atomic Force Microscopy Imaging Mohammad F. Kadir , J M. Edwardson. University of Cambridge, Cambridge, United Kingdom. Ionotropic glutamate receptors are believed to undergo twisting and shortening upon activation. We used fast-scan atomic force microscopy (AFM) imaging to examine the conformational change of the GluK2 kainate receptor, integrated into a lipid bilayer, in response to activation by the agonist glutamate, either added to the imaging chamber or generated by UV photolysis of caged glutamate. In both cases, the height of the extracellular domain of the receptor fell by 0.8 nm upon activation. In contrast, there was no significant height change in response to glutamate in the presence of the GluK2 antagonist CNQX. Our study represents the first demonstration of the effect of activation on the conformation of GluK2 receptors under near-physiological conditions. 23-POS Board 23 The Binding Affinity of Metal Ions and Leukadherin-1 to CD11bA is Mutually Regulated. Vinay Kumar , Shashank Deep. INDIAN INSTITUTE OF TECHNOLOGY,DELHI, Delhi, India. The binding affinity of leukadherin-1(LA1) with CD11bA is regulated by metal ions and LA-1 also regulates the binding of metal ions with CD11bA. It has been well established that in general, Mn2 + or Mg2 + uniformly facilitate whereas Ca2 + inhibit integrin-ligand interactions in vitro. We measured the affinity of these cations to the inactive and active states of the cation binding αA-domain (CD11bA) from integrin CD11b/CD18 in the absence and presence of the Leukadherin-1(LA-1). Leukadherins are new class of anti-integrin compounds that are integrin agonists, the only true agonists known so far. The information obtained from such studies can be aid in the development of pharmacological compounds as well in the elucidation of factors that determine the specificity of an interaction. ITC and fluorescence measurements showed that Mg2 + and Ca2 + exhibit equivalent affinities to inactive CD11bA but Mn2 + was found to have highest affinity. Binding affinity of Mn2 + or Mg2 + to CD11bA increased substantially on addition to active CD11bA, with no change in that of Ca2 + binding affinity. It was observed that Leukadherin-1 induced a dramatic increase in the binding affinity of all three metal ions (enthalpy driven) to either form of CD11bA and on the other hand, metal ions also increase the binding affinity of LA1 (enthalpy driven) with either form of CD11bA.The increase in the binding affinity of metal ions with CD11bA in the presence of LA1 is consistent with the electronegativity of metal ions in a similar manner as without compound LA1. In the present work, we observed that the compound LA1 plays a critical role in regulation of binding affinity of metal ions to CD11bA and the metal ions itself regulate the binding affinity of Leukadherin-1 to CD11bA.

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