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16. 1. 2017
A growing body of evidence suggests that the regulation of cardiac ryanodine receptor (RYR2) by luminal Ca2+ is mediated by luminal binding sites located on the RYR2 channel itself and/or its auxiliary protein, calsequestrin. The localization and structure of RYR2-resident binding sites are not known because of the lack of a high-resolution structure of RYR2 luminal regions. To obtain the first structural insight, we probed the RYR2 luminal face stripped of calsequestrin by alkaline earth metal divalents (M2+: Mg2+, Ca2+, Sr2+ or Ba2+). We show that the RYR2 response to caffeine at the single-channel level is significantly modified by the nature of luminal M2+. Moreover, we performed competition experiments by varying the concentration of luminal M2+ (Mg2+, Sr2+ or Ba2+) from 8 mM to 53 mM and investigated its ability to compete with 1 mM luminal Ca2+. We demonstrate that all tested M2+ bind to exactly the same RYR2 luminal binding sites. Their affinities decrease in the order: Ca2+ > Sr2+ > Mg2+ ~ Ba2+, showing a strong correlation with the M2+ affinity of the EF-hand motif. This indicates that the RYR2 luminal binding regions and the EF-hand motif likely share some structural similarities because the structure ties directly to the function.
Project: VEGA 2/0006/15, 2/0003/14
Publication: GABURJÁKOVÁ, Jana – GABURJÁKOVÁ, Marta. Cardiac ryanodine receptor: Selectivity for alkaline earth metal cations points to the EF-hand nature of luminal binding sites. In Bioelectrochemistry, 2016, vol. 109, p. 49-56. (3.556 – IF2015). (2016 – Current Contents). ISSN 1567-5394.