Protein Design Group, Centro Nacional de Biotecnología (CNB-CSIC), Cantoblanco, E-28049 Madrid, Spain. sanchez@cnb.uam.es|Protein Design Group, Centro Nacional de Biotecnología (CNB-CSIC), Cantoblanco, E-28049 Madrid, Spain. sanchez@cnb.uam.es|Protein Design Group, Centro Nacional de Biotecnología (CNB-CSIC), Cantoblanco, E-28049 Madrid, Spain. sanchez@cnb.uam.es|Protein Design Group, Centro Nacional de Biotecnología (CNB-CSIC), Cantoblanco, E-28049 Madrid, Spain. sanchez@cnb.uam.es|Protein Design Group, Centro Nacional de Biotecnología (CNB-CSIC), Cantoblanco, E-28049 Madrid, Spain. sanchez@cnb.uam.es