title: Molecular basis for differential modulation of BK channel voltage-dependent gating by auxiliary γ subunits.
abstract: Large conductance Ca(2+)- and voltage-activated potassium (BK) channels are comprised of pore-forming α subunits and various regulatory auxiliary subunits. The BK channel auxiliary γ (BKγ) subunits are a newly identified class of proteins containing an extracellular leucine-rich repeat domain (LRRD), a single transmembrane (TM) segment, and a short cytoplasmic C-terminal tail (C-tail). Although each of the four BKγ proteins shifts the voltage dependence of BK channel activation in a hyperpolarizing direction, they show markedly different efficacies, mediating shifts over a range of 15-145 mV. Analyses of chimeric BKγ subunits created by swapping individual structural elements, and of BKγ deletion and substitution mutants, revealed that differential modulation of BK gating by the four BKγ subunits depends on a small region consisting of the TM segment and the adjacent intracellular cluster of positively charged amino acids. The γ1 and γ2 TM segments contributed approximately -100 mV, and the γ1 and γ3 C-tails contributed approximately -40 mV, to shifting the voltage dependence of BK channel activation, whereas the γ3 and γ4 TM segments and the γ2 and γ4 C-tails contributed much less. The large extracellular LRRDs were mainly functionally interchangeable, although the γ1 LRRD was slightly less effective at enhancing (or slightly more effective at attenuating) the shift in BK channel voltage-dependent gating toward hyperpolarizing potentials than those of the other BKγ subunits. Analysis of mutated BKγ subunits revealed that juxta-membrane clusters of positively charged amino acids determine the functions of the γ1 and γ3 C-tails. Therefore, the modulatory functions of BKγ subunits are coarse- and fine-tuned, respectively, through variations in their TM segments and in the adjacent intracellular positively charged regions. Our results suggest that BK channel modulation by auxiliary γ subunits depends on intra- and/or juxta-membrane mechanisms.
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Center for Neuroscience and Pain Research, The University of Texas MD Anderson Cancer Center, Houston, TX 77030.
authors.forename: Qin
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Center for Neuroscience and Pain Research, The University of Texas MD Anderson Cancer Center, Houston, TX 77030.
authors.forename: Fei
authors.initials: F
authors.lastname: Fan
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Center for Neuroscience and Pain Research, The University of Texas MD Anderson Cancer Center, Houston, TX 77030.
authors.forename: Ha Rim
authors.initials: HR
authors.lastname: Kwak
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Center for Neuroscience and Pain Research, The University of Texas MD Anderson Cancer Center, Houston, TX 77030 Program in Neuroscience, University of Texas Graduate School of Biomedical Sciences, Houston, TX 77225 jyan1@mdanderson.org.
authors.forename: Jiusheng
authors.initials: J
authors.lastname: Yan
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D021122:Protein Subunits; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: C494841:KCNMA1 protein, human; C539913:LRRC26 protein, human; C573836:LRRC38 protein, human; C573834:LRRC52 protein, human; C573835:LRRC55 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D021122:Protein Subunits; D011188:Potassium