Recent Advancements in HiSOR-VUVCD
Spectrophotometer for Characterizing BiomoleculeStructures
Koichi Matsuo & Mohamed Ibrahim
Hiroshima Synchrotron Radiation Center, 2-313 Kagamiyama, Higashi-Hiroshima,Hiroshima, 739-0046, Japan
Circular dichroism (CD), which refers to the difference in absorbance between left- and right-circularly
polarized light, is a well-established technique for monitoring the steric structures of chiral molecules,
particularly biomolecules (e.g., natural products, proteins, DNA, and polysaccharides). The usage ofsynchrotron radiation (SR) as a light source has further enhanced the usefulness of this spectroscopic
method. This enhancement includes extending the wavelength range of CD spectra into vacuum-ultraviolet(VUV) region (down to 140 nm) [1, 2], developments of new VUV-CD analytical methods combined withcomputational science, and the installation of the linear dichroism (LD) and spatial- and time-resolved
measurement systems. In this study, we introduce the recent progress in VUVCD techniques using SR inHiSOR for characterizing the structures of biomolecules.
The relationship between chromophores of steric configurations and their substituents in organiccompounds or natural products can be analyzed based on the sign of CD (positive or negative). For
instance, the absorption of allene occurred around 180 nm, and the absolute configuration of its
substituents was determined from the CD sign in the VUV region [3]. Similarly, acetal bonds and hydroxyl
groups of sugars also exhibited CD peaks around 170 nm. However, determining configurations from theCD sign was a challenge, as even mono-saccharides exist in an equilibrium state composed of six isomers.
While molecular dynamics simulation and time-dependent density functional theory have successfully
reproduced the unique CD of each isomer, disclosing their steric configurations including intra- and intermolecular hydrogen bonding network [4].
The CD analysis of globular proteins combined with bioinformatics and LD enables estimating of thecontents, numbers of segments, sequences, and orientations of secondary structures of proteins. This
combination method was applied to elucidate the mechanism of protein-membrane interaction related todrug transportation into cell, myelin formation around neuron cells, and antimicrobial activity in immune
system [5,6,7]. Further, the time-resolved system installed into the CD instrument realized the kinetics
analysis of conformational changes of protein during membrane interaction processes. The use of micro
beam with Schwarzschild objective or lenses enables CD measurement of microvolume rare sample andposition-dependent CD. This system facilitated elucidating the mechanism of DNA damage response in Xray irradiated human HeLa cells [8] as well as measuring the spatial-resolved CD of liquid and solid
samples.
VUVCD analysis was extended to investigate the structuration of microbial exopolysaccharides (EPS)
sourced from the marine environment, along with biocompatible polymers (i.e., bioplastics) synthesized bybacteria. Structural variations due to sample sources, concentrations, and pH levels, as well as theircompatibility with cell membranes, were examined to compare their distinct biological functions, such as
proinflammatory activity [9,10].
The CD technique with SR light source would further enhance the performance of chiral spectroscopy
and open a pathway of next-generation of molecular chirality research.
References:[1] K. Matsuo, K. Gekko, Bull. Chem. Soc. Jpn., 6, 675 (2013); [2] K. Matsuo, K. Gekko, Meth. Mol. Biol., 2003, 253(2019); [3] T. Umezawa, N. Mizutani, K. Matsuo, Y. Tokunaga, F. Matsuda, T. Nehira, Molecules, 26, 1296 (2021); [4] K.
Matsuo, K. Gekko, J. Phys. Chem. A, 124, 642 (2020); [5] K. Matsuo, M. Kumashiro, K. Gekko, Chirality, 32, 594 (2020)[6] M. Kumashiro, Y. Izumi, K. Matsuo, Proteins, 89, 1251 (2021); [7] M. Kumashiro, R. Tsuji, S. Suenaga, K. Matsuo,Membranes, 12, 131 (2022); [8] Y. Izumi, K. Matsuo, A. Yokoya, Chirality, 35, 165 (2023); [9]Y. ElHalmouch, H.A.H. Ibrahim, N.M. Dofdaa, M.E.M. Mabrouk, M.M.
ElMetwally, T. Nehira,K. Ferji, Y. Ishihara,K. Matsuo, M.I.A. Ibrahim, Carbohydr. Polym., 311, 120743 (2023); [10] M.E. Esmael, M.I.A. Ibrahim, S.A.
Aldhumri, R.A. Bayoumi, K. Matsuo, A.M. Khattab, Int. J. Biol. Macromol., 242, 124721 (2023).