Extracting Intramolecular Sequence Information from Intermolecular Distributions: Highly Nonrandom Methylester Substitution Patterns in Homogalacturonans Generated by Pectinmethylesterase

The ratio of the two component sugar residues comprising the anionic polysaccharide homogalacturonan (HG; namely, methylesterified or unmethylesterifed galacturonic acid (GalA)) has been controlled chemically or enzymatically in order to produce samples comprised of varying degrees and distributions of methylesterification (DM). Capillary electrophoresis (CE) has been used to characterize the samples produced and, by mapping the measured electrophoretic mobilities to biopolymer charge density, intermolecular distributions of the DM have been extracted. For chemically modified samples with random intramolecular patterns of methylesterification, the experimentally extracted intermolecular DM distributions agree well with the predictions of calculations based on the binomial theorem, demonstrating that the random nature of the demethylesterification process and, hence, the intramolecular DM patterns themselves, are directly reflected in the intermolecular distribution. Furthermore, this principle has been demonstrated by extending the work to the study of substrates with highly nonrandom DM distributions generated using a processive plant-pectinmethylesterase (pPME). An ensemble of polymer chains, generated in silico by a simulation optimized to match the experimentally measured intermolecular DM distribution, contains all possible information regarding the substrate and can further be interrogated to obtain, for example, the full Gal-A blocklength distribution.