Isoform-specific differences between the type I alpha and II alpha cyclic AMP-dependent protein kinase anchoring domains revealed by solution NMR

Cyclic AMP dependent protein kinase (PKA) is controlled, in part, by the su bcellular localization of the enzyme (1). Discovery of dual Specificity anc horing proteins (D-AKAPs) indicates that not only is the type II, but also the type I, enzyme localized (2). It appears that the type I enzyme is loca lized in a novel, dynamic fashion as opposed to the apparent static localiz ation of the type II enzyme. Recently, the structure of the dimerization/do cking (D/D) domain from the type II enzyme was solved (3), This work reveal ed an X-type four-helix bundle motif with a hydrophobic patch that modulate s AKAP interactions. To understand the dynamic versus static localization o f PKA, multidimensional NMR techniques were used to investigate the structu ral features of the type I D/D domain. Our results indicate a conserved hel ix-turn-helix motif in the type I and type II D/D domains. However, importa nt differences between the two-domains are evident in the extreme NH2 termi nus: this region is extended in the type II domain, whereas it is helical i n the type I protein. The NH2-terminal residues in RII alpha contain determ inants for anchoring, and the orientation and packing of this helical eleme nt in the RI alpha structure may have profound consequences in:the recognit ion surface presented to the AKAPs.