Structural and electron-microscopic studies of jacalin from jackfruit (Artocarpus integrifolia) show that this lectin is a 65 kDa tetramer.
The 133-amino-acid sequences of the alpha-subunit of jacalin (a lectin from Artocarpus integrifolia) and of the slightly larger alpha'-subunit were determined. The alpha'- and alpha-subunits, in the approximate ratio of 1:3, were found to be virtually identical in their primary structures, except for one valine for isoleucine substitution at position 113. Although both alpha'- and alpha-chains were glycosylated, the extent of glycosylation in the alpha'-chain was much greater than that in the alpha-subunit. In the alpha'-polypeptide, all molecules contained an N-linked oligosaccharide at position 74 and some contained sugar at position 43. The alpha- and alpha'-subunits were found to be strongly non-covalently associated with three distinct beta-subunits containing 20 amino acids each. Electron-microscopic visualization of native jacalin disclosed a structure composed of four alpha-type subunits with a clear-cut 4-fold symmetry. Analytical-ultracentrifugation studies of jacalin revealed an average molecular mass of 65 kDa, a value compatible with a tetrameric structure of the alpha(alpha')-subunits. The recalculated number of sugar-binding sites per jacalin molecule, given a molecular mass of 65 kDa, would yield 0.8 sites per alpha(alpha')-promoter, i.e. about twice the value previously determined [Appukutan & Basu (1985) FEBS Lett. 180, 331-334; Ahmed & Chatterjee (1989) J. Biol. Chem. 264, 9365-9372].
Ruffet
E
E
Department of Medical Biochemistry, University of Geneva, Switzerland.
Paquet
N
N
Frutiger
S
S
Hughes
G J
GJ
Jaton
J C
JC
D000595:Amino Acid Sequence; D002241:Carbohydrates / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D003488:Cyanogen Bromide; D004591:Electrophoresis, Polyacrylamide Gel; D037102:Lectins / Q000737:chemistry* / Q000648:ultrastructure; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000302:isolation & purification; D037121:Plant Lectins; D010944:Plants
D002241:Carbohydrates; D037102:Lectins; D046911:Macromolecular Substances; D010446:Peptide Fragments; D037121:Plant Lectins; C043696:jacalin; D003488:Cyanogen Bromide