Communication between N terminus and loop2 tunes Orai activation Article

Fahrner, M, Pandey, SK, Muik, M et al. (2018). Communication between N terminus and loop2 tunes Orai activation . JOURNAL OF BIOLOGICAL CHEMISTRY, 293(4), 1271-1285. 10.1074/jbc.M117.812693

cited authors

  • Fahrner, M; Pandey, SK; Muik, M; Traxler, L; Butorac, C; Stadlbauer, M; Zayats, V; Krizova, A; Plenk, P; Frischauf, I; Schindl, R; Gruber, HJ; Hinterdorfer, P; Ettrich, R; Romanin, C; Derler, I



  • Ca2 release-activated Ca2 (CRAC) channels constitute the major Ca2 entry pathway into the cell. They are fully reconstituted via intermembrane coupling of the Ca2-selective Orai channel and the Ca2-sensing protein STIM1. In addition to the Orai C terminus, the main coupling site for STIM1, the Orai N terminus is indispensable for Orai channel gating. Although the extended transmembrane Orai N-terminal region (Orai1 amino acids 73–91; Orai3 amino acids 48 – 65) is fully conserved in the Orai1 and Orai3 isoforms, Orai3 tolerates larger N-terminal truncations than Orai1 in retaining store-operated activation. In an attempt to uncover the reason for these isoform-specific structural requirements, we analyzed a series of Orai mutants and chimeras. We discovered that it was not the N termini, but the loop2 regions connecting TM2 and TM3 of Orai1 and Orai3 that featured distinct properties, which explained the different, isoform-specific behavior of Orai N-truncation mutants. Atomic force microscopy studies and MD simulations suggested that the remaining N-terminal portion in the non-functional Orai1 N-truncation mutants formed new, inhibitory interactions with the Orai1-loop2 regions, but not with Orai3-loop2. Such a loop2 swap restored activation of the N-truncation Orai1 mutants. To mimic interactions between the N terminus and loop2 in full-length Orai1 channels, we induced close proximity of the N terminus and loop2 via cysteine cross-linking, which actually caused significant inhibition of STIM1-mediated Orai currents. In aggregate, maintenance of Orai activation required not only the conserved N-terminal region but also permissive communication of the Orai N terminus and loop2 in an isoform-specific manner.

publication date

  • January 26, 2018

published in

Digital Object Identifier (DOI)

start page

  • 1271

end page

  • 1285


  • 293


  • 4