Structural investigations on the Nodal-Cripto binding: a theoretical and experimental approach.

Nodal, a member of the transforming growth factor-β superfamily, is a potent embryonic morphogen also implicated in tumor progression. Up to date structural information on the interaction of Nodal with its molecular partners are unknown. To deepen our understanding about mechanisms underlying both embryonic development and Nodal/Cripto-dependent tumor progression, we present here a molecular model of activin receptor-like kinase 4/Cripto/Nodal complex built by homology modeling as well as docking tests aimed at identifying potential binding epitopes. Starting from this model, we have predicted a large interaction surface on Nodal, which encompasses residues 43-69 and includes the prehelix loop and the H3 helix. This hypothesis has been subsequently assessed by surface plasmon resonance binding assays between the full-length Cripto and synthetic peptides reproducing the selected Nodal regions. In addition, the binding affinity between the full-length Nodal and Cripto proteins has been evaluated for the first time.