5c1c

Publication Abstract from PubMed

Many pectin methylesterases (PMEs) are expressed in plants to modify plant cell-wall pectins for various physiological roles. These pectins are also attacked by PMEs from phytopathogens and phytophagous insects. The de-methylesterification by PMEs of the O6-methylester groups of the homogalacturonan (HG) component of pectin, exposing galacturonic acids, can occur processively or non-processively, respectively describing sequential versus single de-methylesterification events occurring before enzyme-substrate dissociation. The high-resolution X-ray structures of a PME from Aspergillus niger in deglycosylated and Asn-linked N-acetylglucosamine-stub forms reveal a 10(2/3)-turn parallel beta helix (similar to but with less extensive loops than bacterial, plant and insect PMEs). Capillary electrophoresis shows that this PME is non-processive, halophilic and acidophilic. Molecular-dynamics simulations and electrostatic-potential calculations reveal very different behavior and properties compared to processive PMEs. Specifically, uncorrelated rotations are observed about the glycosidic bonds of a partially de-methylesterified decasaccharide model substrate, in sharp contrast to the correlated rotations of processive PMEs, and the substrate-binding groove is negatively not positively charged.

Structure and Properties of Non-Processive, Salt-Requiring, Acidophilic Pectin Methylesterases from Aspergillus niger Provides Insights into the Key Determinants of Processivity Control.,Kent LM, Loo TS, Melton LD, Mercadante D, Williams MA, Jameson GB J Biol Chem. 2015 Nov 14. pii: jbc.M115.673152. PMID:26567911^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.