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BIOGRAPHY:
Dr. Frasch is Director of the Institute for Research in
Biotechnology, National University of General San Martin; Professor,
Department of Biological Sciences, University of Buenos Aires; and
Career Researcher, Research Career Department, National Research
Council, Buenos Aires. Dr. Frasch received a Ph.D. in cell biology in
1977 from the University of Buenos Aires. He did postdoctoral work in
the Netherlands at the University of Amsterdam and in the United States
at the University of Oregon. He was head of the Molecular Biology
Laboratory at the Institute of Biochemistry Research, Campomar
Foundation, Buenos Aires, from 1986 to 1996. From 1990 to 1993 he
chaired the TDR/WHO Steering Committee on Chagas' disease, and since
1994 he has co-chaired its Committee on Parasite Genomes. Dr. Frasch
received the Luis F. Leloir Award in 1993, the 2000 Award in Biology
from the Third World Academy of Sciences, a 2001 Guggenheim Fellowship,
and the 2003 Merit Diploma in Cytology and Molecular Biology from the
Konex Foundation in Argentina. He was first awarded an HHMI
International Research Scholar grant in 1997. He works on
Trypanosoma cruzi mucins and trans-sialidase surface
molecules.
RESEARCH ABSTRACT SUMMARY:
Structure, Protein Engineering and Inhibitors of the Trypanosoma cruzi Virulence Factor Trans-Sialidase
American (Trypanosoma cruzi) and African (T. brucei)
trypanosomes express a surface trans-sialidase (TS), a unique enzyme
that transfers sialic acid from host glycoconjugates to terminal
galactoses in surface parasite molecules. In T. cruzi, TS has
relevant functions in cell infection and protection of the parasite and
is involved in the pathology caused by the trypanosome. The relevant
functions of TS make it a good target for the development of
alternative chemotherapies against the infection. We have recently
obtained the crystal structure of the T. cruzi enzyme
(Buschiazzo et al., Mol. Cell 10:757, 2002), which has allowed
us to identify critical residues in the sialic acid and galactose
binding sites. This information allowed the characterization of the
catalytic nucleophile (Watts et al., J. Am. Chem. Soc.
125:7532–7533, 2003) and the construction of mutants with the aim of
obtaining trans-sialylation activity from a sialidase scaffold (Paris
et al., submitted). Five point mutations were enough to obtain a
sialidase mutant with trans-sialidase activity, but a sixth mutation
reduced the activity to about 10 percent of that present in the
wild-type TS. The structure obtained prompted us to test compounds for
their biological activity. Given that the galactose site is unique to
TS, lactose derivatives able to compete with the widely used acceptor
acetyllactosamine were tested. The glucose open-chain derivatives
lactitol and lactobionic acid were found to be good acceptors of sialic
acid. In vivo, lactitol effectively inhibited both the transfer of
sialic acid to acetyllactosamine and the re-sialylation of parasite
mucins. Lactitol also diminished T. cruzi infection in cultured
Vero cells by 20–27 percent. These results indicate that
structure-based design of lactose derivatives might allow the
identification of compounds directed to the lactose-binding site of TS
to prevent parasite sialylation and, thus, infection.
Photo: Dominic Chaplin, Pine Creek Pictures
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