Hinge-Motion Binding Proteins: Unraveling Their Analytical Potential

Abstract

C hemical analysis has benefited significantly from recent advances in instrumentation that enhance detection sensitivity. The complexity of sample matrices and the presence of compounds structurally related to an analyte dictate the need for sensitive and selective methods that can discriminate the analyte from interferences. Research has focused on the discovery of synthetic molecular recognition systems, referred to as host-guest chemistry, as well as the identification of biological recognition systems. Among such biomolecules, hinge-motion binding proteins (HMBPs) demonstrate exquisite selectivity toward their corresponding ligand/analyte, with affinities K D down to the nanomolar range. These proteins are so named because they undergo a significant conformational change upon binding of the ligand-the two domains bend around a "hinge" region of the protein. The binding mechanism of these proteins resembles that of the carnivorous plant commonly known as the Venus flytrap.The conformational change that HMBPs undergo upon binding of a ligand can be used to quantify a target analyte. In one approach, a reporter group, such as a fluorescent probe, is strategically positioned on the protein so that it experiences a change in its microenvironment as a result of a binding event (Figure 1a). Another method involves protein chimeras, in which the HMBP is fused with other proteins and the signal is transduced upon binding with the target analyte (Figure 1b). In a third technique, the HMBP can be labeled with a reporter molecule, which moves as a result of the binding event either closer to or further away from the signal transducer (Figure 1c). A fourth strategy uses the conformational change to enable the expression of a reporter molecule through a transcriptional regulation mechanism (Figure 1d).Different classes of HMBPs include periplasmic binding proteins; transcriptional regulators; enzymes; and messenger proteins, like calmodulin (1). This article focuses on periplasmic binding proteins and calmodulin, because they have already been applied to environmental and metabolite monitoring, food technology, bioanalysis, high-throughput screening, and diagnostics.Hinge-motion binding proteins undergo a conformational change that can be used as the basis for quantifying analytes.

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