The relation between lignin sequence and its 3D structure.

BACKGROUND Lignin, the second most abundant biopolymer on earth, plays a major structural role in plants, conferring mechanical strength and regulating water conduction. Understanding the three-dimensional structure of lignin is important for fundamental reasons as well as engineering plants towards lignin valorization. Lignin lacks a specific primary sequence, making its average chemical composition the focus of most recent studies. However, it remains unclear whether the 3D structure of lignin molecules depends on their sequence. METHODS We performed all-atom molecular dynamics simulation of three S/G-lignin molecules with the same average composition but different sequence. RESULTS A detailed statistical analysis of the radius of gyration and relative shape anisotropy reveals that the lignin sequence has no statistically significant effect on the three-dimensional structure. We found however, that homopolymers of C-lignin with the same molecular weight have smaller radii of gyration than S/G-lignin. We attribute this to lower hydroxyl content of C-lignin, which makes it more compact and rigid. CONCLUSIONS The 3D structure of lignin is influenced by the overall content of monomeric units and interunit linkages and not by its precise primary sequence. General significance Lignin is assumed to not have a well-defined primary structure. The results presented here demonstrate there are no significant differences in the 3D structure of lignin molecules with the same average composition but different primary sequence.