Degradation of Human Serum Albumin by Infrared Free Electron Laser Enhanced by Inclusion of a Salen-Type Schiff Base Zn (II) Complex.

Yuika Onami,Takashiro Akitsu,Koichi Tsukiyama,Takayasu Kawasaki,Hiroki Aizawa,Mauricio A Palafox,Tomoyuki Haraguchi

doi:10.3390/ijms21030874

Abstract

A salen-type Schiff base Zn(II) complex included in human serum albumin (HSA) protein was examined by UV-Vis, circular dichroism (CD), and fluorescence (PL) spectra. The formation of the composite material was also estimated by a GOLD program of ligand–protein docking simulation. A composite cast film of HSA and Zn(II) complex was prepared, and the effects of the docking of the metal complex on the degradation of protein molecules by mid-infrared free electron laser (IR-FEL) were investigated. The optimum wavelengths of IR-FEL irradiation to be used were based on experimental FT-IR spectra and vibrational analysis. Using TD-DFT results with 6-31G(d,p) and B3LYP, the IR spectrum of Zn(II) complex could be reasonably assigned. The respective wavelengths were 1652 cm−1 (HSA amide I), 1537 cm−1 (HSA amide II), and 1622 cm−1 (Zn(II) complex C=N). Degradation of HSA based on FT-IR microscope (IRM) analysis and protein secondary structure analysis program (IR-SSE) revealed that the composite material was degraded more than pure HSA or Zn(II) complex; the inclusion of Zn(II) complex enhanced destabilization of folding of HSA.

Highlights

In recent years, researches on artificial metalloenzymes, namely, docking metal complexes to proteins, such as bio-inspired catalysts, drug discovery, and biofuel cells have attracted increased attention [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
The low value of the charge on the hydrophobic benzene rings of Zn(II) complex (ZnL) complexes facilitates that complexes appear to be circled by the hydrophobic region of the human serum albumin (HSA) molecules, as we found by docking calculations (Section 2.3.2)
We revealed the docking of ZnL into HSA by using UV-Vis, PL, circular dichroism (CD), and docking simulation with GOLD

Summary

Introduction

Researches on artificial metalloenzymes, namely, docking metal complexes to proteins, such as bio-inspired catalysts, drug discovery, and biofuel cells have attracted increased attention [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Since typical Schiff base complexes are relatively simple in structure and easy to synthesize, they can be applied in various fields. In this way, the potential of materials with metal complexes docked to proteins is expanding. Tokyo University of Science possesses an infrared free electron laser (IR-FEL) oscillation facility, called “FEL-TUS”. It is a synchrotron radiation-based coherent laser that has an adjustable wavelength in the mid-infrared region (5 to 10 μm) and oscillates with picosecond pulses. IR-FEL has been well used to ablate biological tissues in medicine, molecular interaction of proteins with intense infrared radiation has been less studied [20,21,22] contrary to UV light [23,24]

Methods

Results

Conclusion