Synthesis and solution-phase conformation of the RG-I fragment of the plant polysaccharide pectin reveals a modification-modulated assembly mechanism.
The syntheses of pure RG-I fragments of key plant matrix biomolecule pectin using a counterintuitive late-stage convergent cis-glycosylation has allowed detailed analyses of their solution-phase conformations, metal binding affinities, pK(a) values, self-assembly equilibria, and diffusional kinetics. These reveal a striking, right-handed 3(1)-helix that provides an effective and repeating lateral display of putative liganding carboxylates. Moreover, these heteropolymeric structures allow units as short as tetrasaccharides to self-assemble through carbohydrate-carbohydrate interactions that are induced by the presence of Ca(II), a known dynamic trigger in planta. These self-assembly properties can be switched simply by the addition or removal of a single methyl group in this repeating unit through methyl (de)esterification, another known dynamic trigger in planta. Together, the combined effect of Ca(II) and methylation revealed here suggests a concerted molecular basis for these two major dynamic modifications in planta.
Scanlan
Eoin M
EM
Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK.
Mackeen
Mukram M
MM
Wormald
Mark R
MR
Davis
Benjamin G
BG
D008968:Molecular Conformation; D010368:Pectins / Q000138:chemical synthesis* / Q000737:chemistry; D010944:Plants / Q000737:chemistry*
C042491:rhamnogalacturonan I; D010368:Pectins