A dihydropyridine receptor α1s loop region critical for skeletal muscle contraction is intrinsically unstructured and binds to a SPRY domain of the type 1 ryanodine receptor

• DOI: 10.1016/j.biocel.2008.08.004
• Publication Date: 2008-08-13T21:42:15Z
• Authors: Yanfang Cui; Han-Shen Tae; Nicole C. Norris; Yamuna Karunasekara; Pierre Pouliquin; Philip G. Board; Angela F. Dulhunty; Marco G. Casarotto
• Keywords: 0301 basic medicine; Calcium Channels, L-Type; RyR; Mutant Chimeric Proteins; Intrinsically unstructured protein; In Vitro Techniques; 1,4 dihydropyridine receptor alpha 1s; Protein Structure, Secondary; 03 medical and health sciences; sprouty protein; Protein-protein interaction; calcium channel L type; ryanodine receptor; calcium ion; Animals; Humans; membrane protein; Protein Interaction Domains and Motifs; Muscle, Skeletal; SPRY1 protein; chimeric protein; Binding Sites; huma DHPR; Membrane Proteins; Ryanodine Receptor Calcium Release Channel; ryanodine receptor 1; phosphoprotein; Phosphoproteins; Magnetic Resonance Imaging; NMR; unclassified drug; Keywords: 1,4 dihydropyridine receptor; Mutagenesis, Site-Directed; Crystallization; Muscle Contraction; Protein Binding

The II-III loop of the dihydropyridine receptor (DHPR) alpha(1s) subunit is a modulator of the ryanodine receptor (RyR1) Ca(2+) release channel in vitro and is essential for skeletal muscle contraction in vivo. Despite its importance, the structure of this loop has not been reported. We have investigated its structure using a suite of NMR techniques which revealed that the DHPR II-III loop is an intrinsically unstructured protein (IUP) and as such belongs to a burgeoning structural class of functionally important proteins. The loop does not possess a stable tertiary fold: it is highly flexible, with a strong N-terminal helix followed by nascent helical/turn elements and unstructured segments. Its residual structure is loosely globular with the N and C termini in close proximity. The unstructured nature of the II-III loop may allow it to easily modify its interaction with RyR1 following a surface action potential and thus initiate rapid Ca(2+) release and contraction. The in vitro binding partner for the II-III was investigated. The II-III loop interacts with the second of three structurally distinct SPRY domains in RyR1, whose function is unknown. This interaction occurs through two preformed N-terminal alpha-helical regions and a C-terminal hydrophobic element. The A peptide corresponding to the helical N-terminal region is a common probe of RyR function and binds to the same SPRY domain as the full II-III loop. Thus the second SPRY domain is an in vitro binding site for the II-III loop. The possible in vivo role of this region is discussed.