Life science
Medical & healthcare, Food products

Kinetics of conformational change of multiple helicalpolysaccharides
Department of Macromolecular Science, Graduate School of ScienceProfessor Ken Terao
https://researchmap.jp/kenteraoLife science

AbstractXanthan is a double helical polysaccharide. It is widely used forfood additives because the dilute solution has significantly highviscosity. Circular dichroism (CD) and small-angle X-ray scattering(SAXS) measurements were made for three xanthan samples inaqueous NaCl after rapid temperature change to investigate thekinetics of the conformational change between the ordered anddisordered states. After the rapid heating, the CD signal mainly
regarding the carbonyl groups on the side chains quickly changed
within 150 s while the SAXS intensity reflecting the main-chain conformation decreased more gradually. This shows the intermediate
conformation (loose double helix). The SAXS profile in the rapid
cooling process showed that the loose double helical structure wasformed within 150 s, but the CD signal slowly changed with around2 days to recover the native local conformation.

▍ Background & Results
DNA, collagen, and polysaccharides have multiple helix structure with high rigidity in water. In recent years, multiple helices
consisting of polysaccharides and DNA were developed for genedelivery materials. However, since multiple helical polysaccharides
are simple homopolymers with the equivalent repeating units,
branched and hairpin like superstructures can be found for renatured samples. In order to control the renatured conformations, it isimportant to investigate their kinetics to form the multiple helices.
We thus made time-resolved small-angle X-ray scattering measurements for double helical xanthan whose chemical structure isshown in Figure 3 to observe the conformational change processes
by using the synchrotron radiation at SPring-8. Considering the CD
signal reflects the chiral structure of the chromophores, temperature change of the CD signal of xanthan shows the conformationalchange of side groups. While this is consistent with the double
helix content at the equilibrium state, we found that clear differences were found just after the temperature change. Carbonyl side
chains immediately became more fluctuating after rapid heating,whereas the rodlike double helical conformation observed fromSAXS was maintained at least several minutes. On the other hand,
while the rodlike double helix formed in a short time range after therapid cooling, it took more than one day to recover the CD signal.
In the near future, we would like to clarify the relationship between
this intermediate structure and the obtained hairpin/hyperbranching structures.

tures, such as hairpin-like or hyperbranched structures, during theirrefolding process. Considering the functionalities can be related tothe superstructures, elucidating the kinetics of molecular morphology changes, including intermediate structures, will provide useful
information to develop the new functionalities of xanthan.

Figure 1. Schematic representation of conformational change after rapid heating
and cooloing processes and the time constants.

Figure 2. Possible conformations of xanthan through denature and renature processes.

▍ Significance of the research and Future perspective
The melting and refolding of the multiple helical structures areusually studied using spectroscopic methods such as CD. We
showed that SAXS profile is a more direct measure of the double
helix contents. Significantly different kinetics between CD andSAXS clearly indicated that the existence of the intermediate conformation. It is known that xanthan can form specific superstruc-Figure 3. Chemical structure of xanthan.

P a t e n t
Tomofuji, Yu; Matsuo, Koichi; Terao, Ken. Kinetics of denaturation and renaturation processes of double-stranded helical polysaccharide, xanthan inaqueous sodium chloride. Carbohydr. Polym., 275, 118681. doi: 10.1016/j.carbpol.2021.118681
UR
L https://www.chem.sci.osaka-u.ac.jp/lab/terao/
K e y w o r d multiple helical polymers, polysaccharides, molecular conformations, food additives
Tr e a t i s e