Purification, identification and preliminary crystallographic characterization of a novel seed protein from Vigna unguiculata

A tropical legume, Vigna unguiculata, was explored in order to identify potential allergens among the abundant seed proteins and to attempt their crystallographic study. Salt fractionation of the seed extract followed by chromatographic separation led to the purification of a 25 kDa protein. Gel-filtration chromatography of the 80% ammonium sulfate precipitation fraction led to separation of this protein in pure form, which was subjected to N-terminal sequencing. The N-terminal sequences of internal fragments of this protein showed 85% homology to mung bean seed albumin. This family of proteins is known to be intrinsically allergenic. Rhombic shaped crystals were obtained that diffracted to about 2.1 Å resolution. The crystals belong to space group C2 and have unit-cell parameters a = 124.9, b = 60.1, c = 67.5 Å, β = 111.1°.