Three residues in the luminal domain of triadin impact on Trisk 95 activation of skeletal muscle ryanodine receptors.
Triadin isoforms, splice variants of one gene, maintain healthy Ca2+homeostasis in skeletal muscle by subserving several functions including an influence on Ca2+release through the ligand-gated ryanodine receptor (RyR1) ion channels. The predominant triadin isoform in skeletal muscle, Trisk 95, activates RyR1 in vitro via binding to previously unidentified amino acids between residues 200 and 232. Here, we identify three amino acids that influence Trisk 95 binding to RyR1 and ion channel activation, using peptides encompassing residues 200-232. Selective alanine substitutions show that K218, K220, and K224together facilitate normal Trisk 95 binding to RyR1 and channel activation. Neither RyR1 binding nor activation are altered by alanine substitution of K220alone or of K218and K224. Therefore K218, K220, and K224contribute to a robust binding and activation site that is disrupted only when the charge on all three residues is neutralized. We suggest that charged pair interactions between acidic RyR1 residues D4878, D4907, and E4908and Trisk 95 residues K218, K220, and K224facilitate Trisk 95 binding to RyR1 and channel activation. Since K218, K220, and K224are also required for CSQ binding to RyRs (Kobayashi et al. 17, J Biol Chem 275, 17639-17646), the results suggest that Trisk 95 may not simultaneously bind to RyR1 and CSQ, contrary to the widely held belief that triadin monomers form a quaternary complex with junctin, CSQ and RyR1. Therefore, the in vivo role of triadin monomers in modulating RyR1 activity is likely unrelated to CSQ.
John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia.
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John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia. Angela.dulhunty@anu.edu.au.|John Curtin School of Medical Research, Australian National University, PO Box 334, Canberra, ACT, 2601, Australia. Angela.dulhunty@anu.edu.au.
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Dulhunty
Health Research Institute, Faculty of Education Science and Mathematics, University of Canberra, Bruce, ACT, 2617, Australia.
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Beard
D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002155:Calsequestrin / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008297:Male; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*
D002155:Calsequestrin; D002352:Carrier Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C070048:triadin
Calcium signaling; Ryanodine receptor calcium release channels; Skeletal muscle; Triadin