Investigating metal-binding in proteins by nuclear magnetic resonance

Abstract

Metal ions play a key role for the function of many proteins. The interaction of the metal ion with the protein and its involvement in the function of the protein vary widely. In some proteins, the metal ion is bound tightly to the ligand residues and may be the key player in the function of the protein, as in the case of blue copper proteins. In other proteins, the metal ion is bound only temporarily and loosely to the protein, as in the case of some metalloenzymes and other proteins where the metal ion acts as a cofactor necessary for the function of the protein. Such proteins are often known as metal ion-activated proteins. The review focuses on recent nuclear magnetic resonance (NMR) studies of a series of metal-dependent proteins and the characterization of the metal-binding sites. In particular, we focus on NMR techniques for studying metal binding to proteins such as chemical shift mapping, paramagnetic NMR and changes in backbone dynamics upon metal binding.

A comprehensive platform to investigate protein–metal ion interactions by affinity capillary electrophoresis

“…Most of the useful techniques require pure sample for analysis such as Xray crystallography, nuclear magnetic resonance (NMR), Fourier transform infra-red spectroscopy (FTIR), circular dichroism (CD) spectroscopy, surface plasmon resonance (SPR) and atomic force microscopy (AFM) [9,10]. NMR technique performs with highly concentrated samples, and is restricted for small and soluble proteins (<40 kDa) due to often observed spectral overlaps for large proteins [11]. The preparation of biological crystal for X-ray crystallography is predominately difficult and in some cases impossible [9].…”

Assessing the fractions of tautomeric forms of the imidazole ring of histidine in proteins as a function of pH

“…This is mainly because of the chemical versatility of its imidazole ring, which includes two neutral, chemically distinct forms, and a protonated form, referred to as N δ1 -H and N ϵ2 -H tautomers, and H þ , respectively, with one form favored over the other by the protein environment and pH. Moreover, His with a pK°of 6.6 (2) titrates around neutral pH, allowing the deprotonated nitrogen of its imidazole ring to serve as an effective ligand for metal binding (3). In particular, it has been suggested that tautomerization and variations of χ1 of His are crucial parts of the proton-transfer process (4).…”

Paramagnetic Tools in Protein NMR

“…However, since the 1990s techniques have been developed to use the paramagnetic cofactor to retrieve structural restraints to solve metal binding site structures. Some excellent reviews are available explaining how to use a paramagnetic cofactor to deliver structural restraints [14,17,[112][113][114][115].…”