A solid-state NMR study of the structure and dynamics of the myristoylated N-terminus of the guanylate cyclase-activating protein-2.

Guanylate cyclase-activating protein-2 (GCAP-2) is a retinal Ca(2+) sensor protein. It plays a central role in shaping the photoreceptor light response and in light adaptation through the Ca(2+)-dependent regulation of the transmembrane retinal guanylate cyclase (GC). GCAP-2 is N-terminally myristoylated and the full activation of the GC requires this lipid modification. The structural and functional role of the N-terminus and particularly of the myristoyl moiety is currently not well understood. In particular, detailed structural information on the myristoylated N-terminus in the presence of membranes was not available. Therefore, we studied the structure and dynamics of a 19 amino acid peptide representing the myristoylated N-terminus of GCAP-2 bound to lipid membranes by solid-state NMR. (13)C isotropic chemical shifts revealed a random coiled secondary structure of the peptide. Peptide segments up to Ala(9) interact with the membrane surface. Order parameters for Calpha and side chain carbons obtained from DIPSHIFT experiments are relatively low, suggesting high mobility of the membrane-associated peptide. Static (2)H solid-state NMR measurements show that the myristoyl moiety is fully incorporated into the lipid membrane. The parameters of the myristoyl moiety and the DMPC host membrane are quite similar. Furthermore, dynamic parameters (obtained from (2)H NMR relaxation rates) of the peptide's myristic acid chain are also comparable to those of the lipid chains of the host matrix. Therefore, the myristoyl moiety of the N-terminal peptide of GCAP-2 fills a similar conformational space as the surrounding phospholipid chains.