Solution structure of extracellular loop of human β4 subunit of BK channel and its biological implication on ChTX sensitivity

• Published in: Scientific reports 2018-03, Vol.8 (1), p.4571-4571, Article 4571
• Main Authors: Wang, Yanting, Lan, Wenxian, Yan, Zhenzhen, Gao, Jing, Liu, Xinlian, Wang, Sheng, Guo, Xiying, Wang, Chunxi, Zhou, Hu, Ding, Jiuping, Cao, Chunyang
• Format: Article
• Language: English
• Subjects: 631/45/269/1151; 631/535/878/1263; Calcium channels (voltage-gated); Calcium conductance; Channel gating; Charybdotoxin; Charybdotoxin - chemistry; Charybdotoxin - metabolism; Conduction; Cryoelectron Microscopy; Deactivation; Disulfide bonds; Disulfides - chemistry; Humanities and Social Sciences; Humans; Kinetics; Large-Conductance Calcium-Activated Potassium Channels - chemistry; Large-Conductance Calcium-Activated Potassium Channels - genetics; Large-Conductance Calcium-Activated Potassium Channels - metabolism; Mass Spectrometry; Mass spectroscopy; Models, Molecular; multidisciplinary; NMR; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular; Potassium; Potassium channels (calcium-gated); Potassium channels (voltage-gated); Protein Structure, Tertiary; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - metabolism; Recombinant Proteins - biosynthesis; Recombinant Proteins - chemistry; Recombinant Proteins - isolation & purification; Science; Science (multidisciplinary); Titration; Toxins
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-23016-y

Large-conductance Ca 2+ - and voltage-dependent K + (BK) channels display diverse biological functions while their pore-forming α subunit is coded by a single Slo1 gene. The variety of BK channels is correlated with the effects of BKα coexpression with auxiliary β (β1-β4) subunits, as well as newly defined γ subunits. Charybdotoxin (ChTX) blocks BK channel through physically occluding the K + -conduction pore. Human brain enriched β4 subunit (hβ4) alters the conductance-voltage curve, slows activation and deactivation time courses of BK channels. Its extracellular loop (hβ4-loop) specifically impedes ChTX to bind BK channel pore. However, the structure of β4 subunit’s extracellular loop and the molecular mechanism for gating kinetics, toxin sensitivity of BK channels regulated by β4 are still unclear. To address them, here, we first identified four disulfide bonds in hβ4-loop by mass spectroscopy and NMR techniques. Then we determined its three-dimensional solution structure, performed NMR titration and electrophysiological analysis, and found that residue Asn123 of β4 subunit regulated the gating and pharmacological characteristics of BK channel. Finally, by constructing structure models of BKα/β4 and thermodynamic double-mutant cycle analysis, we proposed that BKα subunit might interact with β4 subunit through the conserved residue Glu264(BKα) coupling with residue Asn123(β4).