1. Department of Biochemistry, Institute of Chemistry, University of São Paulo, P.O. Box 26077, 05513-970, São Paulo, Brazil, and Department of Experimental Medicine, Section on Chemistry and Structural Biochemistry, University of Parma, 43100, Parma, Italy, and Centre for Molecular and Structural Biology, CeBiME, LNLS, 13084-971, Campinas, Brazil