Topology of the polypeptide chain in the complex of agglutinin from castorbean seeds with beta-D-galactose in the crystalline state

The three-dimensional structure of the complex of agglutinin from Ricinus c ommunis with beta -D-galactose was established and refined at 2.5 Angstrom resolution by X-ray structure analysis. Biocrystals were obtained using dia lysis through a semipermeable membrane. X-ray intensity data (R-merge = 4.6 %) were collected from one crystal at 100 K using synchrotron radiation at the DESY outstation [European Molecular Biology Laboratory (EMBL), Hamburg, Germany]. The initial phases were calculated by the molecular replacement method. The atoms of both protein and sugar molecules were localized, Unlik e ricin, the ricinlike heterodimer RcA contains only one galactose-binding center in the region of the Asn46-Gly25-Trp37-Lys40 site in the first domai n of the B subunit, whereas the second galactose-binding site of the B subu nit is lost, One functionally important water molecule, which is bound to t he residues Tyr123-Glu176-Arg179-Glu207, was revealed in the region of the active center in the A subunit. (C) 2001 MAIK "Nauka/Interperiodica".