Crystal structures of recombinant and native soybean β‐conglycinin β homotrimers

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Abstract
The crystal structures of recombinant and native β homotrimers of soybean β‐conglycinin were determined by X‐ray crystallography at 2.7 and 2.8 Å resolutions, respectively. The crystals of the recombinant and native β homotrimers belong to space group P21 with cell parameters a = 80.51 Å, b = 63.48 Å, c = 131.43 Å, and β = 90.01° and with cell parameters a = 82.78 Å, b = 69.47 Å, c = 125.33 Å and β= 97.22°, respectively. The β monomers consist of amino‐terminal and carboxyl‐terminal modules that are very similar to each other and are related by a pseudo‐dyad axis. Each module of the β monomer is subdivided into a core and a loop domain. These structural features of both β homotrimers are consistent with those of canavalin and phaseolin, which are similar vicilin class proteins. The superposition of the models of the native and recombinant β monomers shows a root mean square deviation of 0.43–0.51 Å for 343 common Cα atoms within 2.0 Å. This result indicates that the N‐linked glycans do not influence the final structure of the β homotrimer. Comparison of the models of β‐conglycinin, phaseolin and canavalin indicates that β‐conglycinin resembles canavalin rather than phaseolin, and that canavalin and phaseolin differ the most among them. The evolutional relationships are discussed.