MS04-P03 Crystallographic and calorimetric studies with nuclear transport of DNA repair proteinsThe DNA damage can occur by several agents which may promote instability of the genome leading to several diseases such as cancer, neurological disorders, immunodeficiencies and premature aging. To avoid this serious consequences, cells have evolved a number of DNA repair pathways, which carry out the process in multiple steps to repair specific DNA damage, and maintain the integrity of the genome. The nuclear import is a pre requisite for the functions of DNA repair proteins and their correct location is essential. The classical nuclear import pathway is the best characterized and, probably the most used protein import mechanism to the cell nucleus, which involves the binding of the cargo protein via nuclear localization sequence (NLS) recognized by the importin-α protein (Impα). Classical nuclear localization sequences are targeting signals that link the cargo proteins to the Impα import receptor. They are formed by one or two basic clusters of amino acid residues, termed monopartite or bipartite NLSs. Aiming to understand the structural basis of the nuclear import process of DNA repair proteins, we have used X-ray crystallography and calorimetric tools to study the interaction between Impα and the NLS regions of each protein. Five different complexes have been studied, which cover the most important DNA mechanisms: i) base excision repair (BER) - FEN1 protein, ii) nucleotide excision repair (NER) - XPG protein, iii) mismatch repair (MMR) - PMS2/MLH1 heteodimer and iv) non-homologous end joining (NHEJ) - Ku70/Ku80 hetorodimer. We demonstrated that all these proteins are able to be transported to the cell nucleus by classical nuclear import pathway using monopartide or bipartite NLS sequences. However, we demonstrated that, for many of these proteins, the NLS regions are different from the previously described data in literature. In addition, new structural features related to minor and linker NLS binding regions were observed, which may give specificity for the transport of different DNA repair proteins.References:
 Christie, M. et al. (2016)J Mol Biol, 428 2060-2090.
 de Barros, A.C. et al. (2016) J Mol Biol, 428 2120-2131.
 de Barros, A.C. et al. (2012) Acta Crystallogr D Biol Crystallogr, 68 743-750.Keywords: importin-alpha, Nuclear transport, DNA repair proteins