title: Selecting ions by size in a calcium channel: the ryanodine receptor case study.
abstract: Many calcium channels can distinguish between ions of the same charge but different size. For example, when cations are in direct competition with each other, the ryanodine receptor (RyR) calcium channel preferentially conducts smaller cations such as Li(+) and Na(+) over larger ones such as K(+) and Cs(+). Here, we analyze the physical basis for this preference using a previously established model of RyR permeation and selectivity. Like other calcium channels, RyR has four aspartate residues in its GGGIGDE selectivity filter. These aspartates have their terminal carboxyl group in the pore lumen, which take up much of the available space for permeating ions. We find that small ions are preferred by RyR because they can fit into this crowded environment more easily.
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois. Electronic address: dirk_gillespie@rush.edu.
authors.forename: Dirk
authors.initials: D
authors.lastname: Gillespie
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Le
authors.initials: L
authors.lastname: Xu
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meissner
mesh_terms: D015640:Ion Channel Gating; D017136:Ion Transport; D008954:Models, Biological; D010539:Permeability; D016062:Porosity; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel