Structural and functional characterization of signaling protein complexes

Abstract

The Ras/ERK pathway is a ubiquitous kinase cascade, so regulation of this pathway is critically improtant. Examples from two regulatory proteins, c-Cbl and calmodulin are presented. c-Cbl is an E3 ubiquitin ligase and a major regulator of tyrosine kinases. Through x-ray crystallography of five Cbl-TKB:phosphopeptide complexes, the mechanism by which the Cbl-TKB domain binds to its substrates is through a conserved, specificity determining intrapeptidyl hydrogen bond was uncovered. The ability of Cbl to bind in a reverse orientation to atypical binding motifs of certain substrates was also uncovered (Ng et al., EMBO J 2008, 27: 804-816). Calmodulin is a protein that confers calcium sensitivity when bound to its substrates. All voltage-gated sodium channels possess the IQ motif for binding to calmodulin but are each differently regulated. Through biophysical and computational analyses, the mode of calmodulin binding to two high affinity sodium channel isoforms Nav1.4 and Nav1.6 was characterized.