Dissecting ITC data of metal ions binding to ligands and proteins

Abstract

Background: ITC is a powerful technique that can reliably assess the thermodynamic underpinnings of a wide range of binding events. When metal ions are involved, complications arise in evaluating the data due to unavoidable solution chemistry that includes metal speciation and a variety of linked equilibria.

Scope of review: This paper identifies these concerns, provides recommendations to avoid common mistakes, and guides the reader through the mathematical treatment of ITC data to arrive at a set of thermodynamic state functions that describe identical chemical events and, ideally, are independent of solution conditions. Further, common metal chromophores used in biological metal sensing studies are proposed as a robust system to determine unknown solution competition.

Major conclusions: Metal ions present several complications in ITC experiments. This review presents strategies to avoid these pitfalls and proposes and experimentally validates mathematical approaches to deconvolute complex equilibria that exist in these systems.

General significance: This review discusses the wide range of complications that exists in metal-based ITC experiments. It provides a starting point for scientists new to this field and articulates concerns that will help experienced researchers troubleshoot experiments.

Keywords: Bioinorganic chemistry; Calorimetry; ITC; Metal competition; Metal speciation; Proton competition.