Seminars Archive
M. Vijayan
Abstract
Wednesday, February 7, 2001, 15:00
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Structural Diversity and carbohydrate specificity of Lectins
M. Vijayan
(Molecular Biophysics unit, Indian Institute of Science, Bangalore)
ABSTRACT
Lectins are carbohydrate binding proteins involved in several hysiological
processes. They are essentially recognition molecules and
their ability to bind different carbohydrate structures with exquisite
specificity has received considerable attention. However, they exhibit
substantial variability in structure and strategies for generating
carbohydrate specificity. This is exemplified by the structural studies
on
lectins being carried out in this laboratory. The tetrameric peanut
lectin has an unusual `open` quaternary structure. Its enhanced specificity
for
the tumour associated disaccharide T-antigen over and above that for
other disaccharides, is generated by water bridges. The structure of this
lectin
and those from winged beans demonstrate that legume lectins are a family
of proteins in which small alterations in essentially the same tertiary
structure, consequent to sequence variations, lead to large changes
in quaternary association. Structures of the monosaccharide complexes of
winged bean lectin also lead to valuable insights into their blood
group specificities. The crystal structure analysis of jacalin, one of
the two
lectins from jack fruit seeds, led to the identification of a new lectin
fold. The structure also demonstrates how carbohydrate specificity could
be generated by a post-translational modification. Artocarpin, the
other lectin from jack fruit seeds, is structurally homologous to jacalin,
in
spite of the different carbohydrate specificities. A comparison of
the structure of garlic lectin, analysed in this laboratory, with that
of the
homologous snow drop lectin, indicates that carbohydrate specificity
could be generated by oligomerisation as well.
