Molecular Recognition of the Disordered Dihydropyridine Receptor II-III Loop by a Conserved SPRY Domain of the Type 1 Ryanodine Receptor

1. The dihydropyridine receptor (DHPR) II¿III loop is an intrinsically unstructured region made up of a-helical and b-turn secondary structure elements with the N and C termini in close spatial proximity. 2. The DHPR II¿III loop interacts in vitro with a ryanodine receptor (RyR) 1 SPRY domain through a-helical segments located in the A and B regions. Mutations within the A and B regions in the DHPR II¿III loop alter the binding affinity to the SPRY2 domain. 3. The A and C peptides derived from DHPR II¿III loop show negative cooperativity in binding to the SPRY2 domain. 4. The SPRY2 domain of the RyR1 (1085¿1208) forms a b-sheet sandwich structure flanked by variable loop regions. An acidic loop region of SPRY2 (1107¿1121) forms part of a negatively charged cleft that is implicated in the binding of the DHPR II¿III loop. 5. The mutant E1108A located in the negatively charged loop of SPRY2 reduces the binding affinity to the DHPR II¿III loop.