Periplasmic Binding Proteins in Thermophiles: Characterization and Potential Application of an Arginine-Binding Protein from Thermotoga maritima: A Brief Thermo-Story

Abstract

Arginine-binding protein from the extremophile Thermotoga maritima is a 27.7 kDa protein possessing the typical two-domain structure of the periplasmic binding proteins family. The protein is characterized by a very high specificity and affinity to bind to arginine, also at high temperatures. Due to its features, this protein could be taken into account as a potential candidate for the design of a biosensor for arginine. It is important to investigate the stability of proteins when they are used for biotechnological applications. In this article, we review the structural and functional features of an arginine-binding protein from the extremophile Thermotoga maritima with a particular eye on its potential biotechnological applications.

Figure 1

3D cartoon models of TmArgBP in the absence (A) and in the presence (B) of arginine (displayed in spheres). The ligand-binding induces the bending of the two domains that makes the protein assumes the closed form.

Figure 2

Close-up view of TmArgBP binding site with bound arginine. All the amino acidic residues lying within a distance of 5 Å from the ligand arginine are shown and represented in stick mode and labeled, while arginine is displayed in spheres. All the possible interactions that can be formed given charge, position and distance of each residue from the arginine are displayed in dashed lines.

Figure 3

Position of Trp²²⁶ in TmArgBP. The indole side chain is in evidence, displayed in sticks and labeled. Panel A and B depict the open and closed form, respectively. The residue is far from the binding site and enough buried from the aqueous interface to avoid the direct exposition to the solvent. Notice that the presence of the ligand (displayed in spheres) does not affect the Trp²²⁶ position.

Figure 4

Close-up view of Trp²²⁶ microenvironment. Trp²²⁶ and the residues that possibly interact with it are in evidence, displayed in sticks and labeled. The black dashed lines represent the distances between the functional groups involved in the Trp²²⁶ stabilizing interactions. A and B show the tryptophan microenvironment for open and closed form, respectively. The interaction distances, labeled in the figure, remain roughly unvaried.