Crystal structures of recombinant and native soybean beta-conglycinin betahomotrimers

The crystal structures of recombinant and native beta homotrimers of soybea n beta -conglycinin were determined by X-ray crystallography at 2.7 and 2.8 Angstrom resolutions, respectively. The crystals of the recombinant and na tive beta homotrimers belong to space group P2(1) with cell parameters a = 80.51 Angstrom, b = 63.48 Angstrom, c = 131.43 Angstrom, and beta = 90.01 d egrees and with cell parameters a = 82.78 Angstrom, b = 69.47 Angstrom, c = 125.33 Angstrom and beta = 97.22 degrees, respectively. The beta monomers consist of amino-terminal and carboxyl-terminal modules that are very simil ar to each other and are related by a pseudo-dyad axis. Each module of the beta monomer is subdivided into a core and a loop domain. These structural features of both beta homotrimers are consistent with those of canavalin an d phaseolin, which are similar vicilin class proteins. The superposition of the models of the native and recombinant beta monomers shows a root mean s quare deviation of 0.43-0.51 Angstrom for 343 common C alpha atoms within 2 .0 Angstrom. This result indicates that the N-linked glycans do not influen ce the final structure of the beta homotrimer. Comparison of the models of beta -conglycinin, phaseolin and canavalin indicates that beta -conglycinin resembles canavalin rather than phaseolin, and that canavalin and phaseoli n differ the most among them. The evolutional relationships are discussed.