A mechanism of global shape-dependent recognition and phosphorylation of filamin by protein kinase A [Signal Transduction]

February 9th, 2015 by Ithychanda, S. S., Fang, X., Mohan, M. L., Zhu, L., Tirupula, K. C., Prasad, S. V. N., Wang, Y.-X., Karnik, S., Qin, J.

Protein phosphorylation mediates essentially all aspects of cellular life. In human, this is achieved by ~500 kinases, each recognizing a specific consensus motif (CM) in the substrates. Majority of CMs are surface exposed, which are thought to be accessible to kinases for phosphorylation. Here we have investigated the archetypical protein kinase A (PKA) mediated phosphorylation of filamin, a major cytoskeletal protein that can adopt an autoinhibited conformation. Surprisingly, autoinhibited filamin is refractory to phosphorylation by PKA on a known S2152 site despite its CM being exposed and corresponding peptide being phosphorylated. Structural analysis revealed that while the CM fits into the PKA active site, its surrounding regions sterically clash with the kinase. However, upon ligand binding, filamin undergoes a conformational adjustment, allowing rapid phosphorylation on S2152. These data uncover a novel ligand induced conformational switch to trigger filamin phosphorylation. They further suggest a substrate shape-dependent filtering mechanism that channels specific exposed CM/kinase recognition in diverse signaling responses.