title: Tetrameric mouse acetylcholinesterase: continuum diffusion rate calculations by solving the steady-state Smoluchowski equation using finite element methods.
abstract: The tetramer is the most important form for acetylcholinesterase in physiological conditions, i.e., in the neuromuscular junction and the nervous system. It is important to study the diffusion of acetylcholine to the active sites of the tetrameric enzyme to understand the overall signal transduction process in these cellular components. Crystallographic studies revealed two different forms of tetramers, suggesting a flexible tetramer model for acetylcholinesterase. Using a recently developed finite element solver for the steady-state Smoluchowski equation, we have calculated the reaction rate for three mouse acetylcholinesterase tetramers using these two crystal structures and an intermediate structure as templates. Our results show that the reaction rates differ for different individual active sites in the compact tetramer crystal structure, and the rates are similar for different individual active sites in the other crystal structure and the intermediate structure. In the limit of zero salt, the reaction rates per active site for the tetramers are the same as that for the monomer, whereas at higher ionic strength, the rates per active site for the tetramers are approximately 67%-75% of the rate for the monomer. By analyzing the effect of electrostatic forces on ACh diffusion, we find that electrostatic forces play an even more important role for the tetramers than for the monomer. This study also shows that the finite element solver is well suited for solving the diffusion problem within complicated geometries.
authors.affiliation: Howard Hughes Medical Institute, University of California at San Diego, La Jolla, California 92093, USA. dzhang@mccammon.ucsd.edu
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
authors.forename: Jason
authors.initials: J
authors.lastname: Suen
authors.forename: Yongjie
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Song
authors.forename: Zoran
authors.initials: Z
authors.lastname: Radic
authors.forename: Palmer
authors.initials: P
authors.lastname: Taylor
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Holst
authors.forename: Chandrajit
authors.initials: C
authors.lastname: Bajaj
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Baker
authors.forename: J Andrew
authors.initials: JA
authors.lastname: McCammon
mesh_terms: D000109:Acetylcholine / Q000032:analysis / Q000737:chemistry*; D000110:Acetylcholinesterase / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure; D000818:Animals; D001665:Binding Sites; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D003461:Crystallography / Q000379:methods; D004058:Diffusion; D020342:Finite Element Analysis; D007700:Kinetics; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D046912:Multiprotein Complexes; D000110:Acetylcholinesterase; D000109:Acetylcholine