A unique set of SH3–SH3 interactions controls IB1 homodimerization

Abstract

Islet-brain 1 (IB1 or JIP-1) is a scaffold protein that interacts with components of the c-Jun N-terminal kinase (JNK) signal-transduction pathway. IB1 is expressed at high levels in neurons and in pancreatic b-cells, where it controls expression of several insulin-secretory components and secretion. IB1 has been shown to homodimerize, but neither the molecular mechanisms nor the function of dimerization have yet been characterized. Here, we show that IB1 homodimerizes through a novel and unique set of Src homology 3 (SH3)-SH3 interactions. X-ray crystallography studies show that the dimer interface covers a region usually engaged in PxxP-mediated ligand recognition, even though the IB1 SH3 domain lacks this motif. The highly stable IB1 homodimer can be significantly destabilized in vitro by three individual point mutations directed against key residues involved in dimerization. Each mutation reduces IB1-dependent basal JNK activity in 293T cells. Impaired dimerization also results in a reduction in glucose transporter type 2 expression and in glucose-dependent insulin secretion in pancreatic b-cells. Taken together, these results indicate that IB1 homodimerization through its SH3 domain has pleiotropic effects including regulation of the insulin secretion process.

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

“…However, the SH3 domain of JIP1 is unique: it is incapable of binding to Pro-rich motifs and its purpose is to provide a specific dimerization interface for JIP1/2 proteins. Considering that the KLC1-kinesin 1 complexes are also dimeric, this is consistent with the requirement for JIP1 dimerization (133). An extensive region preceding the SH3 domain also appears to be conserved and is likely folded.…”

An unrecognized extracellular function for an intracellular adapter protein released from the cytoplasm into the tumor microenvironment

“…With rCRKL (GST and His-tag), our results suggest that CRKL can oligomerize (Fig. S7), perhaps through the SH3 domains (24,36,37).…”

SH3 domains: modules of protein–protein interactions

“…All SH3 residues of the Islet brain 1 (IB1) protein involved in dimerization are also those that usually interact with PPII ligands (Kristensen et al 2006). In contrast, Dictyostelium discoideum myosin VII interacts with its own adjacent proline-rich (PxxP) region at the site distant from the conserved PxxP binding site ).…”

“…The link between the structural motif and regulation by phosphorylation highlights four motifs: WW2, SH2, SH3, and PDZ (Akiva et al 2012). Regulation by the association of SH3 domains also occurs via the formation of homodimers (IB1 protein; Kristensen et al 2006) or heterodimers (VAV N-terminal and GRB2 Cterminal SH3 domains complex; Nishida et al 2001). In IB1 protein, the dimer interface and PxxP binding occupy the same site even though the IB1 protein does not contain the PxxP motif; therefore, ligands compete with IB1 protein.…”

“…In IB1 protein, the dimer interface and PxxP binding occupy the same site even though the IB1 protein does not contain the PxxP motif; therefore, ligands compete with IB1 protein. All of the SH3 residues of IB1 involved in dimerization are also those that usually interact with PPII ligands (Kristensen et al 2006).…”