{"id":6141,"date":"2023-02-17T07:02:42","date_gmt":"2023-02-17T07:02:42","guid":{"rendered":"https:\/\/beta.nanion.de\/resource_library\/2016-distinct-regions-that-control-ion-selectivity-and-calcium-dependent-activation-in-the-bestrophin-ion-channel\/"},"modified":"2023-02-17T07:02:42","modified_gmt":"2023-02-17T07:02:42","slug":"2016-distinct-regions-that-control-ion-selectivity-and-calcium-dependent-activation-in-the-bestrophin-ion-channel","status":"publish","type":"resource_library","link":"https:\/\/nanion.com\/zh-hans\/resource_library\/2016-distinct-regions-that-control-ion-selectivity-and-calcium-dependent-activation-in-the-bestrophin-ion-channel\/","title":{"rendered":"2016 &#8211; Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel"},"content":{"rendered":"<p>Abstract:\u00a0Cytoplasmic calcium (Ca<sup>2+<\/sup>) activates the bestrophin anion channel, allowing chloride ions to flow down their electrochemical gradient. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Previously, we determined an X-ray structure of chicken BEST1 that revealed the architecture of the channel. Here, we present electrophysiological studies of purified wild-type and mutant BEST1 channels and an X-ray structure of a Ca<sup>2+<\/sup>-independent mutant. From these experiments, we identify regions of BEST1 responsible for Ca<sup>2+<\/sup>\u00a0activation and ion selectivity. A \u201cCa<sup>2+<\/sup>\u00a0clasp\u201d within the channel\u2019s intracellular region acts as a sensor of cytoplasmic Ca<sup>2+<\/sup>. Alanine substitutions within a hydrophobic \u201cneck\u201d of the pore, which widen it, cause the channel to be constitutively active, irrespective of Ca<sup>2+<\/sup>. We conclude that the primary function of the neck is as a \u201cgate\u201d that controls chloride permeation in a Ca<sup>2+<\/sup>-dependent manner. In contrast to what others have proposed, we find that the neck is not a major contributor to the channel\u2019s ion selectivity. We find that mutation of a cytosolic \u201caperture\u201d of the pore does not perturb the Ca<sup>2+<\/sup>\u00a0dependence of the channel or its preference for anions over cations, but its mutation dramatically alters relative permeabilities among anions. The data suggest that the aperture functions as a size-selective filter that permits the passage of small entities such as partially dehydrated chloride ions while excluding larger molecules such as amino acids. Thus, unlike ion channels that have a single \u201cselectivity filter,\u201d in bestrophin, distinct regions of the pore govern anion-vs.-cation selectivity and the relative permeabilities among anions.Significance:BEST1 is a Ca<sup>2+<\/sup>-activated chloride channel found in a variety of cell types that allows chloride to traverse the plasma membrane. Mutations in BEST1 can cause macular degeneration. The mechanisms for anion selectivity and Ca<sup>2+<\/sup>-dependent activation of BEST1 are unknown. Here, we show that a hydrophobic \u201cneck\u201d region of the channel\u2019s pore does not play a major role in ion selectivity but acts as an effective gate, responding to Ca<sup>2+<\/sup>\u00a0binding at a cytosolic sensor. Mutation of a cytosolic \u201caperture\u201d dramatically affects relative permeabilities among anions. These insights help rationalize how disease-causing mutations in BEST1 affect channel behavior and contribute to a broader understanding of ion channel gating and selectivity mechanisms.<\/p>\n","protected":false},"featured_media":0,"template":"","products_tags":[45],"resource_type":[75],"application_areas":[50],"therapeutic_areas":[],"target_categories":[335],"target_families":[367],"targets":[265],"resource_keyword":[],"class_list":["post-6141","resource_library","type-resource_library","status-publish","hentry","products_tags-port-a-patch","resource_type-publication","application_areas-ion-channels","target_categories-intracellular-regulated-ion-channels","target_families-cacc-channels","targets-best1"],"acf":[],"_links":{"self":[{"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/resource_library\/6141","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/resource_library"}],"about":[{"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/types\/resource_library"}],"wp:attachment":[{"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/media?parent=6141"}],"wp:term":[{"taxonomy":"products_tags","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/products_tags?post=6141"},{"taxonomy":"resource_type","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/resource_type?post=6141"},{"taxonomy":"application_areas","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/application_areas?post=6141"},{"taxonomy":"therapeutic_areas","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/therapeutic_areas?post=6141"},{"taxonomy":"target_categories","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/target_categories?post=6141"},{"taxonomy":"target_families","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/target_families?post=6141"},{"taxonomy":"targets","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/targets?post=6141"},{"taxonomy":"resource_keyword","embeddable":true,"href":"https:\/\/nanion.com\/zh-hans\/wp-json\/wp\/v2\/resource_keyword?post=6141"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}