title: Processive pectin methylesterases: the role of electrostatic potential, breathing motions and bond cleavage in the rectification of Brownian motions.
abstract: Pectin methylesterases (PMEs) hydrolyze the methylester groups that are found on the homogalacturonan (HG) chains of pectic polysaccharides in the plant cell wall. Plant and bacterial PMEs are especially interesting as the resulting de-methylesterified (carboxylated) sugar residues are found to be arranged contiguously, indicating a so-called processive nature of these enzymes. Here we report the results of continuum electrostatics calculations performed along the molecular dynamics trajectory of a PME-HG-decasaccharide complex. In particular it was observed that, when the methylester groups of the decasaccharide were arranged in order to mimic the just-formed carboxylate product of de-methylesterification, a net unidirectional sliding of the model decasaccharide was subsequently observed along the enzyme's binding groove. The changes that occurred in the electrostatic binding energy and protein dynamics during this translocation provide insights into the mechanism by which the enzyme rectifies Brownian motions to achieve processivity. The free energy that drives these molecular motors is thus demonstrated to be incorporated endogenously in the methylesterified groups of the HG chains and is not supplied exogenously.
authors: The Riddet Institute, Palmerston North, New Zealand ; School of Chemical Sciences, University of Auckland, Auckland, New Zealand.
authors: Davide
authors: D
authors: Mercadante
authors: The Riddet Institute, Palmerston North, New Zealand ; School of Chemical Sciences, University of Auckland, Auckland, New Zealand.
authors: Laurence D
authors: LD
authors: Melton
authors: The Riddet Institute, Palmerston North, New Zealand ; Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand ; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University, Wellington, New Zealand.
authors: Geoffrey B
authors: GB
authors: Jameson
authors: The Riddet Institute, Palmerston North, New Zealand ; Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand ; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University, Wellington, New Zealand.
authors: Martin A K
authors: MA
authors: Williams
mesh_terms: D055162:Biocatalysis; D001669:Biochemical Phenomena; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D004885:Erwinia / Q000201:enzymology; D006868:Hydrolysis; D008958:Models, Molecular; D009038:Motion; D010368:Pectins; D055672:Static Electricity; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D010368:Pectins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase; C003181:polygalacturonic acid