Preferential Interaction of Beryllium Ion with Carboxylate‐Rich Peptides

Abstract

Glycogen synthase kinase 3β (GSK3β) regulates a number of cellular pathways including glycogen metabolism, the Wnt signaling pathway, and cell proliferation. Hyperactivity of GSK3β has been hypothesized to be potentially related to Alzheimer's disease, bipolar disorder, type II diabetes, and some cancers, therefore GSK3β is of interest as a target for therapeutics. Lithium ion (Li+) is a classical inhibitor of GSK3β, but beryllium ion (Be2+) is approximately 1000‐fold more potent. We are interested in the inhibitory mechanism and thermodynamic characteristics for the metal‐protein binding of Be2+ and GSK3β. Be2+ is believed to inhibit GSK3β by competing for magnesium ion (Mg2+) binding sites that feature aspartic acid (D) or other acidic side chains. As a first step toward understanding how Be2+ could outcompete Mg2+ in metal‐protein interactions, we used model chelating compounds and simple peptides that might partially mimic a carboxylate‐rich binding pocket, and compared their binding properties towards Be2+ and Mg2+. Isothermal titration calorimetry (ITC) binding studies for nitrilotriacetic acid, 4,5‐imidazole dicarboxylic acid, and salicylic acid all showed higher binding affinity for Be2+ compared to Mg2+. ITC binding studies were used to compare Be2+ and Mg2+ interactions with three short peptides: DDDD, GGGG and KKKK. Under the conditions employed, Be2+ exhibited binding with the carboxylate‐rich DDDD peptide while Mg2+ displayed no binding. The neutral tetrapeptide GGGG and the polybasic tetrapeptide KKKK served as negative controls; no metal ion interactions were observed with these peptides in the ITC binding experiments. Further analysis with Be2+ and peptides GDDD and GGDD showed reduced binding affinity compared to DDDD. These results demonstrate that Be2+ has stronger affinity for negatively‐charged carboxylate‐rich peptide sequences compared to Mg2+. This strong affinity may lead to conformational changes that distinguish the inactive Be2+‐GSK3β complex from the active Mg2+‐GSK3β complex. Because GSK3β regulates multiple cellular pathways, the ideal therapeutic inhibitor would lead to selective downstream effects. Investigations using an unusual class of inhibitor like Be2+ might provide insight into the variety of modes potentially available for controlling GSK3β activity.Support or Funding InformationThis work was supported by the U.S. Army Research Laboratory and the U.S. Army Research Office under grant numbers W911NF‐15‐1‐0043 and W911NF‐15‐1‐0216.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.