Bacterial expression, purification and preliminary X-ray crystallographic characterization of the invertase inhibitor Nt-CIF from tobacco.

Acid invertases catalyzing the breakdown of sucrose are regulated at the post-translational level by extracellular inhibitory proteins of 16-20 kDa molecular weight in a pH-dependent manner. Little is known about the characteristics of the underlying protein-protein interaction. Here, the expression, purification, characterization, crystallization and initial X-ray analysis of a biologically active invertase inhibitor Nt-CIF from tobacco is reported. Four crystal forms covering a wide pH range have been obtained and data sets at resolutions higher than 2.5 A have been collected.