Journal
CARBOHYDRATE POLYMERS
Volume 296, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.carbpol.2022.119958
Keywords
Carrageenan; SAXS/WAXS; Molecular dynamics; Metadynamics
Categories
Funding
- NZ synchrotron group
- NeSI
- Ministry of Business, Innovation and Employment
- Ministry of Science and Technology, Taiwan [MOST 105-2221-E-007-137-MY3]
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The traditional notion that.-carrageenan exists in solution as a random coil has been challenged by new research, which shows that the solution-state structure of.-carrageenan retains the helical motifs present in the solid-state. Additionally, there is no evidence to suggest that single chains undergo any conformational transition upon the addition of ions.
The solution state structure of.-carrageenan is typically described as a 'random coil', to indicate a lack of defined secondary structure elements. From this starting point the assignment of an optical-rotation-detected change that follows the introduction of particular ions to such solutions as a 'coil-to-helix transition' seems unambiguous, and thus the canonical description of this important biopolymer's gelling behaviour was born. However, the notion that.-carrageenan exists in solution as a random coil, devoid of secondary structure, has been questioned a number of times previously in the literature, particularly by the molecular modelling and NMR communities. Regrettably, there has been little desire to-date to address these largely overlooked studies or consider their implications for the nature of the so-called 'coil-to-helix transition'. Despite evidence to the contrary, the random-coil-paradigm has prevailed. Here, new data from synchrotron-enabled solution-state x-ray scattering experiments, combined with state-of-the-art atomistic molecular dynamics simulations, are used to show that the solution-state structure of.-carrageenan in fact retains many of the helical motifs present in the solid-state, as inferred from fibre diffraction data. Furthermore, no evidence is found to suggest that single chains undergo any uni-molecular conformational transition upon the addition of ions. These findings once again challenge the paradigm that.-carrageenan exists as a 'random coil' in the solution state, and thereby question the long held assumption that a uni-molecular 'coil-to-helix transition' precedes the dimerization of helices.
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