Novel Mode of Ligand Recognition by the Erbin PDZ Domain

Gabriel Birrane,Judy Chung,John A.A Ladias

doi:10.1074/jbc.c200571200

Abstract

Erbin contains a class I PDZ domain that binds to the C-terminal region of the receptor tyrosine kinase ErbB2, a class II ligand. The crystal structure of the human Erbin PDZ bound to the peptide EYLGLDVPV corresponding to the C-terminal residues 1247-1255 of human ErbB2 has been determined at 1.25-A resolution. The Erbin PDZ deviates from the canonical PDZ fold in that it contains a single alpha-helix. The isopropyl group of valine at position -2 of the ErbB2 peptide interacts with the Erbin Val(1351) and displaces the peptide backbone away from the alpha-helix, elucidating the molecular basis of class II ligand recognition by a class I PDZ domain. Strikingly, the phenolic ring of tyrosine -7 enters into a pocket formed by the extended beta 2-beta 3 loop of the Erbin PDZ. Phosphorylation of tyrosine -7 abolishes this interaction but does not affect the binding of the four C-terminal peptidic residues to PDZ, as revealed by the crystal structure of the Erbin PDZ complexed with a phosphotyrosine-containing ErbB2 peptide. Since phosphorylation of tyrosine -7 plays a critical role in ErbB2 function, the selective binding and sequestration of this residue in its unphosphorylated state by the Erbin PDZ provides a novel mechanism for regulation of the ErbB2-mediated signaling and oncogenicity.

Highlights

From the Molecular Medicine Laboratory and Macromolecular Crystallography Unit, Division of Experimental Medicine, Harvard Institutes of Medicine, Harvard Medical School, Boston, Massachusetts 02115
Since phosphorylation of tyrosine ؊7 plays a critical role in ErbB2 function, the selective binding and sequestration of this residue in its unphosphorylated state by the Erbin PDZ provides a novel mechanism for regulation of the ErbB2-mediated signaling and oncogenicity
The residues at positions 0 and Ϫ2 of the peptide play a critical role in the specificity and affinity of the interaction, whereas it is believed that amino acids upstream of the Ϫ5 position do not interact with PDZ [1,2,3,4,5,6,7]

Summary

Novel Mode of Ligand Recognition by the Erbin PDZ Domain*

Received for publication, October 9, 2002, and in revised form, November 14, 2002. From the Molecular Medicine Laboratory and Macromolecular Crystallography Unit, Division of Experimental Medicine, Harvard Institutes of Medicine, Harvard Medical School, Boston, Massachusetts 02115. Phosphorylation of tyrosine ؊7 abolishes this interaction but does not affect the binding of the four C-terminal peptidic residues to PDZ, as revealed by the crystal structure of the Erbin PDZ complexed with a phosphotyrosine-containing ErbB2 peptide. The Erbin PDZ binds preferentially to the ErbB2 tail having an unphosphorylated tyrosine at position Ϫ7 (corresponding to Tyr1248 in full-length human ErbB2), whereas phosphorylation of this residue reduces significantly the affinity of the Erbin-ErbB2 interaction [8]. A second crystal structure of this domain bound to a phosphotyrosine-containing ErbB2 peptide shows that phosphorylation of Tyr Ϫ7 abrogates its interaction with the ␤2-␤3 loop. These results suggest new mechanisms for regulation of the ErbB2-mediated signaling through its dynamic interaction with the Erbin PDZ

EXPERIMENTAL PROCEDURES

Data collection and phasing

RESULTS AND DISCUSSION