Protein Design Group, CNB-CSIC, Calle Darwin, Cantoblanco 28049 Madrid, Spain. mtress@cnio.es|Protein Design Group, CNB-CSIC, Calle Darwin, Cantoblanco 28049 Madrid, Spain. mtress@cnio.es|Protein Design Group, CNB-CSIC, Calle Darwin, Cantoblanco 28049 Madrid, Spain. mtress@cnio.es|Protein Design Group, CNB-CSIC, Calle Darwin, Cantoblanco 28049 Madrid, Spain. mtress@cnio.es