How do the X-ray Structure and the NMR structure of FMN-binding protein differ?

The crystal structure of FMN-binding protein (FMN-bp) from Desulfovibrio vulgaris Miyazaki F was solved by the multiple isomorphous replacement method and refined to an Ii: factor of 15.1% at 1.3 Angstrom resolution. FMN-bp exists in a dimeric form in the crystal, in contrast to the monomeric structure determined by NMR. R.m.s. deviations between the crystal structure and the solution structure are more than 2 Angstrom, which implies significant differences, There are some hydrophobic residues in the interface between the two monomers. In particular, Leu122 in the C-terminus has a close contact with the o-xylene moiety of FMN, while solvent molecules may cover the o-xylene moiety in the solution structure.