Περίληψη:
Concanavalin A (Con A) is the best-known plant lectin and has important
in vitro biological activities arising from its specific
saccharide-binding ability. Its exact biological role still remains
unknown, The complexes of Con A with
4’-nitrophenyl-alpha-D-mannopyranoside (alpha-PNM) and
4’-nitrophenyl-or-D-glucopyranoside (alpha-PNG) have been crystallized
in space group P2(1)2(1)2 with cell dimensions a = 135.19 Angstrom, b =
155.38 Angstrom, c = 71.25 and a = 134.66 Angstrom, b = 155.67 Angstrom
and c = 71.42 Angstrom, respectively. X-ray diffraction intensities to
2.75 Angstrom for the alpha-PNM and to 3.0 Angstrom resolution for the
alpha-PNG complex have been collected, The structures of the complexes
were solved by molecular replacement and refined by simulated annealing
methods to crystallographic R-factor values of 0.185/0.186 and
free-R-factor values of 0.260/0.274, respectively, In both structures,
the asymmetric unit contains four molecules arranged as a tetramer, with
approximate 222 symmetry, A saccharide molecule is bound in the
sugar-binding site near the surface of each monomer. The nonsugar
(aglycon) portion of the compounds used helps to identify the exact
orientation of the saccharide in the sugar-binding pocket and is
involved in major interactions between tetramers. The hydrogen bonding
network. in the region of the binding site has been analyzed, and only
minor differences with the previously reported Con
A-methyl-alpha-n-mannopyranoside complex structure have been observed.
Structural differences that may contribute to the slight preference of
the lectin for mannosides over glucosides are discussed. Calculations
indicate a negative electrostatic surface potential for the saccharide
binding site of Con A, which may be important for its biological
activity. It is also shown in detail how a particular class of
hydrophobic ligands interact with one of the three so-called
characteristic hydrophobic sites of the lectins. (C) 1996 Academic
Press, Inc.
Συγγραφείς:
Kanellopoulos, PN
Pavlou, K
Perrakis, A
Agianian, B and
Vorgias, CE
Mavrommatis, C
Soufi, M
Tucker, PA and
Hamodrakas, SJ
