Neutron Laue diffraction experiments on a large unit cell: Concanavalin A complexed with methyl-α-D-glucopyranoside

A neutron Laue diffraction experiment on a complex of concanavalin A with methyl-α-D-glucopyranoside extensively soaked in D₂O (space group I2₁3, a = 167.8 Å), which resulted in 3.5 Å diffraction data, is described. In a programme of structural studies of crystalline saccharide complexes of concanavalin A, the unit cell of the cubic I2₁3 complex of concanavalin A with methyl-α-D-glucopyranoside is one of the largest. With its cell edge of 167.8 Å and its asymmetric unit of molecular weight 50 kDa, it represents a challenge for current neutron diffraction technology. The size of the crystal used in this experiment, although large (4 × 3 x × 2 mm), was not the largest ever produced for this complex. The degree of spatial overlapping observed in the Laue experiment, however, suggests that use of larger crystals would be a disadvantage. On the basis of these observations, several technical improvements for macromolecular neutron crystallography are suggested.