The refined structure of canavalin from jack bean in two crystal forms at 2.1 and 2.0 angstrom resolution

The structure of canavalin was refined to 2.1 and 2.0 Angstrom resolution i n cubic and hexagonal crystals of space group P2(1)3 and P6(3), respectivel y. The threefold molecular symmetry is expressed in the symmetry of both cr ystals, where each identical subunit is an asymmetric unit. The canavalin s ubunit consists of two very similar domains, each comprised of a core subdo main having Swiss-roll topology with a loop subdomain that contains helices . The refined canavalin models resolved the discrepancy in amino-acid regis ters of the secondary-structural elements compared with phaseolin. The pres ence of strand Z in both domains of canavalin was confirmed and a new helix in the loop between strands A and B of each domain was observed. The model s were analyzed in terms of the duplicated vicilin domains. Three strictly conserved residues, two glycines and a proline, were identified. The simila rity between entire vicilin molecules is greater than that between separate domains of canavalin and phaseolin, Homology modeling of the sucrose-bindi ng protein (SBP) from soybean showed a plausible trimeric assembly of subun its similar to that of vicilins.