Triadin

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External IDs	GeneCards: [1]
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Species	Human	Mouse
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Triadin, also known as TRDN, is a human gene associated with the release of calcium ions from the sarcoplasmic reticulum triggering muscular contraction through calcium-induced calcium release. Triadin is a multiprotein family, arising from different processing of the TRDN gene on chromosome 6. It is a transmembrane protein on the sarcoplasmic reticulum due to a well defined hydrophobic section and it forms a quaternary complex with the cardiac ryanodine receptor (RYR2), calsequestrin (CASQ2) and junctin proteins. The luminal (inner compartment of the sarcoplasmic reticulum) section of Triadin has areas of highly charged amino acid residues that act as luminal Ca²⁺ receptors. Triadin is also able to sense luminal Ca²⁺ concentrations by mediating interactions between RYR2 and CASQ2. Triadin has several different forms; Trisk 95 and Trisk 51, which are expressed in skeletal muscle, and Trisk 32 (CT1), which is mainly expressed in cardiac muscle.

Interactions

TRDN has been shown to interact with RYR1.

Triadin is required to physically link the RYR2 and CASQ2 proteins, so that RYR2 channel activity can be regulated by CASQ2. The linkage of RYR2 with CASQ2 occurs via highly charged luminal sections of Triadin that are characterized as alternating positively and negatively charged amino acids, known as the KEKE motif.

Luminal concentration levels of Ca²⁺ are sensed by CSQ, and this information is transmitted to RyR via Triadin. At low luminal Ca²⁺ concentrations, Triadin is bound to both RYR2 and CASQ2, so that CSQ prevents RYR2 from opening. At high luminal Ca²⁺ concentrations, Ca²⁺ binding sites on CASQ2 become occupied with Ca²⁺, leading to a weakened interaction between CASQ2 and Triadin. This removes CASQ2’s ability to have an inhibitory effect on the RYR2 channel activity. As more Ca²⁺ binding sites on CASQ2 become occupied, there is an increasing probability of the RYR2 channel being able to open. Eventually, CASQ2 completely dissociates from Triadin and the RYR2 channel becomes completely uninhibited, although Triadin remains bound to RYR2 at all luminal concentrations of Ca²⁺.

Relation to catecholaminergic polymorphic ventricular tachycardia

Most mutations that result in CPVT are found in RYR2 or CASQ2 genes, however a third of CPVT patients have no mutations in either of these proteins, making a mutation in Triadin the most likely cause Because Triadin is necessary in the regulation of Ca²⁺ release by the RyR channel during cardiac contraction, a mutation that prevents Triadin from being formed will make CASQ2 unable to inhibit the RYR2 channel activity, allowing Ca²⁺ leaks and the development of CPVT.

A deletion of amino acids in the TRDN gene can result in an early stop codon. A premature stop codon can either prevent the gene from being translated into the Triadin protein, or can result in a shortened, nonfunctional Triadin protein. A replacement of the amino acid Arginine for the amino acid Threonine at position 59 of the TRDN gene (pT59R) causes instability of Triadin, leading to degradation of the protein. Any of these naturally occurring mutations result in an absence of functional Triadin protein, resulting in CPVT in patients.

Further reading

• Taske NL, Eyre HJ, O'Brien RO, et al. (1995). "Molecular cloning of the cDNA encoding human skeletal muscle triadin and its localisation to chromosome 6q22-6q23". Eur. J. Biochem. 233 (1): 258–65. doi:10.1111/j.1432-1033.1995.258_1.x. PMID 7588753.
• Guo W, Campbell KP (1995). "Association of triadin with the ryanodine receptor and calsequestrin in the lumen of the sarcoplasmic reticulum". J. Biol. Chem. 270 (16): 9027–30. doi:10.1074/jbc.270.16.9027. PMID 7721813.
• Zhang L, Kelley J, Schmeisser G, et al. (1997). "Complex formation between junctin, triadin, calsequestrin, and the ryanodine receptor. Proteins of the cardiac junctional sarcoplasmic reticulum membrane". J. Biol. Chem. 272 (37): 23389–97. doi:10.1074/jbc.272.37.23389. PMID 9287354.
• Caswell AH, Motoike HK, Fan H, Brandt NR (1999). "Location of ryanodine receptor binding site on skeletal muscle triadin". Biochemistry. 38 (1): 90–7. doi:10.1021/bi981306+. PMID 9890886.
• Groh S, Marty I, Ottolia M, et al. (1999). "Functional interaction of the cytoplasmic domain of triadin with the skeletal ryanodine receptor". J. Biol. Chem. 274 (18): 12278–83. doi:10.1074/jbc.274.18.12278. PMID 10212196.
• Sacchetto R, Turcato F, Damiani E, Margreth A (1999). "Interaction of triadin with histidine-rich Ca²⁺-binding protein at the triadic junction in skeletal muscle fibers". J. Muscle Res. Cell. Motil. 20 (4): 403–15. doi:10.1023/A:1005580609414. PMID 10531621.
• Kobayashi YM, Alseikhan BA, Jones LR (2000). "Localization and characterization of the calsequestrin-binding domain of triadin 1. Evidence for a charged beta-strand in mediating the protein-protein interaction". J. Biol. Chem. 275 (23): 17639–46. doi:10.1074/jbc.M002091200. PMID 10748065.
• Kirchhefer U, Neumann J, Baba HA, et al. (2001). "Cardiac hypertrophy and impaired relaxation in transgenic mice overexpressing triadin 1". J. Biol. Chem. 276 (6): 4142–9. doi:10.1074/jbc.M006443200. PMID 11069905.
• Shin DW, Ma J, Kim DH (2001). "The asp-rich region at the carboxyl-terminus of calsequestrin binds to Ca²⁺ and interacts with triadin". FEBS Lett. 486 (2): 178–82. doi:10.1016/S0014-5793(00)02246-8. PMID 11113462.
• Lee HG, Kang H, Kim DH, Park WJ (2001). "Interaction of HRC (histidine-rich Ca²⁺-binding protein) and triadin in the lumen of sarcoplasmic reticulum". J. Biol. Chem. 276 (43): 39533–8. doi:10.1074/jbc.M010664200. PMID 11504710.
• Hong CS, Ji JH, Kim JP, et al. (2002). "Molecular cloning and characterization of mouse cardiac triadin isoforms". Gene. 278 (1–2): 193–9. doi:10.1016/S0378-1119(01)00718-1. PMID 11707337.
• Strausberg RL, Feingold EA, Grouse LH, et al. (2003). "Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences". Proc. Natl. Acad. Sci. U.S.A. 99 (26): 16899–903. Bibcode:2002PNAS...9916899M. doi:10.1073/pnas.242603899. PMC 139241. PMID 12477932.
• Kim E, Shin DW, Hong CS, et al. (2003). "Increased Ca²⁺ storage capacity in the sarcoplasmic reticulum by overexpression of HRC (histidine-rich Ca²⁺ binding protein)". Biochem. Biophys. Res. Commun. 300 (1): 192–6. doi:10.1016/S0006-291X(02)02829-2. PMID 12480542.
• Thevenon D, Smida-Rezgui S, Chevessier F, et al. (2003). "Human skeletal muscle triadin: gene organization and cloning of the major isoform, Trisk 51". Biochem. Biophys. Res. Commun. 303 (2): 669–75. doi:10.1016/S0006-291X(03)00406-6. PMID 12659871.
• Lee JM, Rho SH, Shin DW, et al. (2004). "Negatively charged amino acids within the intraluminal loop of ryanodine receptor are involved in the interaction with triadin". J. Biol. Chem. 279 (8): 6994–7000. doi:10.1074/jbc.M312446200. PMID 14638677.
• Olsen JV, Blagoev B, Gnad F, et al. (2006). "Global, in vivo, and site-specific phosphorylation dynamics in signaling networks". Cell. 127 (3): 635–48. doi:10.1016/j.cell.2006.09.026. PMID 17081983.
• Arvanitis DA, Vafiadaki E, Fan GC, et al. (2007). "Histidine-rich Ca-binding protein interacts with sarcoplasmic reticulum Ca-ATPase". Am. J. Physiol. Heart Circ. Physiol. 293 (3): H1581–9. doi:10.1152/ajpheart.00278.2007. PMID 17526652.

External links

• TRDN human gene location in the UCSC Genome Browser.
• TRDN human gene details in the UCSC Genome Browser.