Spectroscopic/Computational Characterization and the X-ray Structure of the Adduct of the VIVO-Picolinato Complex with RNase A.

Giarita Ferraro,Nicola Demitri,Daniele Sanna,Antonello Merlino,Giuseppe Sciortino,Eugenio Garribba,Luigi Vitale,Valeria Ugone

doi:10.1021/acs.inorgchem.1c02912

Abstract

The structure, stability, and enzymatic activity of the adduct formed upon the reaction of the V–picolinato (pic) complex [VIVO(pic)2(H2O)], with an octahedral geometry and the water ligand in cis to the V=O group, with the bovine pancreatic ribonuclease (RNase A) were studied. While electrospray ionization-mass spectrometry, circular dichroism, and ultraviolet–visible absorption spectroscopy substantiate the interaction between the metal moiety and RNase A, electron paramagnetic resonance (EPR) allows us to determine that a carboxylate group, stemming from Asp or Glu residues, and imidazole nitrogen from His residues are involved in the V binding at acidic and physiological pH, respectively. Crystallographic data demonstrate that the VIVO(pic)2 moiety coordinates the side chain of Glu111 of RNase A, by substituting the equatorial water molecule at acidic pH. Computational methods confirm that Glu111 is the most affine residue and interacts favorably with the OC-6-23-Δ enantiomer establishing an extended network of hydrogen bonds and van der Waals stabilizations. By increasing the pH around neutrality, with the deprotonation of histidine side chains, the binding of the V complex to His105 and His119 could occur, with that to His105 which should be preferred when compared to that to the catalytically important His119. The binding of the V compound affects the enzymatic activity of RNase A, but it does not alter its overall structure and stability.

Highlights

The development of vanadium complexes (VCs) in areas of catalysis, materials science, biology, and medicinal chemistry is a field of extensive research.[1]
The approach was applied to several proteins, such as the hen egg white lysozyme (HEWL),[30−32] myoglobin (Mb),[33] ubiquitin (Ub),[31,32,34] and cytochrome c (Cyt),12f and used to rationalize the spectroscopic data in the literature on blood proteins and enzymes, such as human serum transferrin (HTf),12d human serum albumin (HSA),[19] Hb,12d immunoglobulin G (IgG),12d vanadium bromoperoxidase (VBrPO),12d and VIVO2+-substituted imidazoleglycerolphosphatase dehydratase (IGPD).12d The results suggested that the residues involved in the covalent binding are mainly histidine (His), through the imidazole nitrogen, and aspartate (Asp) or glutamate (Glu), through the carboxylate group
To establish if the interaction of [VIVO(pic)2(H2O)] and RNase A occurs in aqueous solution, ESI-MS(+) spectra were recorded in an ammonium acetate solution and water varying the molar ratio between the VC and the protein (3/1−5/1) at an RNase A concentration of 5 μM

Summary

Introduction

The development of vanadium complexes (VCs) in areas of catalysis, materials science, biology, and medicinal chemistry is a field of extensive research.[1]. Crystals of the adduct formed upon the reaction of [VIVO(pic)2(H2O)] with RNase A were obtained using the soaking strategy: crystals of the metal-free protein grown in 22% PEG4K and 10 mM sodium citrate at pH 5.1 using a protein concentration 1.4 mM have been soaked for 3 days in a solution of the reservoir saturated with the metal complex.

Results

Conclusion