Ca2+ /S100 regulation of giant protein kinases

Protein phosphorylation by protein kinases plays a central regulatory role in cellular processes and these kinases are themselves tightly regulated(1). One common mechanism of regulation involves Ca2+-binding proteins (CaBP) such as calmodulin (CaM)(2). Here we report a Ca2+-effector mechanism for protein kinase activation by demonstrating the specific and >1,000-fold activation of the myosin-associated giant protein kinase twitchin by Ca2+/S100A1(2). S100A1(2) is a member of a large CaBP family that is implicated in various cellular processes, including cell growth, differentiation and motility, but whose molecular actions are largely unknown(3). The S100A1(2)-binding site is a part of the autoregulatory sequence positioned in the active site that is responsible for intrasteric autoinhibition of twitchin kinase; the mechanism of autoinhibition based on the crystal structures of two twitchin kinase fragments is described elsewhere(4). Ca2+/S100 represents a likely physiological activator for the entire family of giant protein kinases involved in muscle contractions and cytoskeletal structure(2,5-9)

Characterizing Protein-Protein Interactions Using Solution NMR Spectroscopy

In this chapter, we describe how NMR chemical shift titrations can be used to study the interaction between two proteins with emphasis on mapping the interface of the complex and determining the bind- ing affinity from a quantitative analysis of the experimental data. In particular, we discuss the appearance of NMR spectra in different chemical exchange regimes (fast, intermediate, and slow) and how these regimes affect NMR data analysis