Cerato-platanin (CP) is a secretion protein produced by the fungal pathogen Ceratocystis platani, the causal agent of the plane canker disease and the first member of the CP family. CP is considered a pathogen-associated molecular pattern because it induces various defense responses in the host, including production of phytoalexins and cell death. Although much is known about the properties of CP and related proteins as elicitors of plant defense mechanisms, its biochemical activity and host target(s) remain elusive. Here, we present the three-dimensional structure of CP. The protein, which exhibits a remarkable pH and thermal stability, has a double ␤-barrel fold quite similar to those found in expansins, endoglucanases, and the plant defense protein barwin. Interestingly, although CP lacks lytic activity against a variety of carbohydrates, it binds oligosaccharides. We identified the CP region responsible for binding as a shallow surface located at one side of the ␤-barrel. Chemical shift perturbation of the protein amide protons, induced by oligo-N-acetylglucosamines of various size, showed that all the residues involved in oligosaccharide binding are conserved among the members of the CP family. Overall, the results suggest that CP might be involved in polysaccharide recognition and that the double ␤-barrel fold is widespread in distantly related organisms, where it is often involved in host-microbe interactions.

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Cellular prion protein (PrPc) is a ubiquitous glycoprotein, whose physiological role is poorly characterized. It has been suggested that PrPc participates in neuritogenesis, neuroprotection, copper metabolism, and signal transduction. In this study we detailed the intracellular events induced by PrPc antibody‐mediated cross‐linking in PC12 cells. We found a Fyn‐dependent activation of the Ras‐Raf pathway, which leads to a rapid and transient phosphorylation of extracellular regulated kinases. In addition, this activation cascade relies on the engagement of integrins, and involves focal adhesion kinase activation. We demonstrated the tyrosine phosphorylation of caveolin‐1 as a consequence of PrPc stimulation, and showed that phosphocaveolin‐1 scaffolds and coordinates protein complexes involved in PrPc‐dependent signaling. Moreover, we found that caveolin‐1 phosphorylation, is a mechanism for recruiting the C‐terminal Src kinase and inactivating Fyn, so as to terminate cell signaling. Furthermore our data support a significant role for PrPc as a response mediator in neuritogenesis and cell differentiation.

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