STRUCTURE AND FOLDING OF THE PROTEINS RACK1 AND ANNEXIN A2

Prof. Travé (Strasbourg) combines protein engineering with biophysical tools to optimise the solubility and solve the structure of difficult-to express proteins related to human pathogenesis. Profs. Raae and Vedeler (Bergen) study the proteins RACK1 and A nnexin A2, respectively. RACK1 binds and regulates many cell targets including Protein Kinase C and the ribosome, and is also targeted by many viruses (HPV, Adenovirus, HIV). RACK1 probably adopts a "beta-propeller" structure with seven four-stranded beta sheets. All the annexins fold as 4 conserved domains of 5 alpha helices each, preceded by a N-terminal arm. Annexins interact with phospholipids in a calcium-dependent manner and bind numerous cellular proteins. The multifunctional Annexin A2 is implicat ed in vesicle transport/fusion, cell signalling, angiogenesis and metastasis. Vedeler and colleagues have discovered that Annexin A2 binds to a specific population of mRNAs. The 3 teams have previously collaborated for producing soluble and folded RACK1 a nd mutants of the RNA-binding site of Annexin A2. Here, we plan to solve the crystal structure of human RACK1, free or in complex with several viral or cellular ligands. In addition, we will use site-directed mutagenesis coupled with biophysical measurem ents and biochemical assays to investigate the role of the N-terminal arm in the folding process of Annexin A2 as well as in the regulation of its RNA-binding activity. This work should bring interesting information on the structure and folding of full- beta and full-alpha multi-repeat proteins. The high-resolution structural analysis of human RACK1 will be essential for understanding the molecular basis of its functions and of their perturbation by different viruses. Finally, a better understanding of A nnexin A2 folding will be important for development of active peptides as anti-angiogenic agents, since Annexin A2 have been suggested to be a putative target for the development of therapeutical drugs.