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