Application of affinity purification methods for analysis of the nitrogenase system from Azotobacter vinelandii

Abstract

Nitrogenases are complex two-component metalloenzymes that catalyze biological nitrogen fixation. Three different nitrogenase types are found in the model nitrogen-fixing microbe Azotobacter vinelandii. In the case of the Mo-dependent enzyme, the two catalytic partners are referred to as the Fe protein and MoFe protein. In addition to genes encoding the catalytic components, there are a total of 68 other gene products known to be variously involved in producing, activating, protecting, sustaining, and regulating formation of the Mo-dependent nitrogenase. In order to support experiments designed to gain insight into the catalytic mechanism and assembly of nitrogenase, four different affinity-based purification protocols have been developed. These include an improved Co²⁺-based Immobilized Metal Affinity Chromatography (IMAC) method for the purification of MoFe protein, a newly developed StrepTactin Affinity Chromatography (STAC) method for the purification of MoFe protein and its assembly intermediates, a combined IMAC and STAC method for isolation of highly pure MoFe protein, and a STAC-based bait-prey method for isolation of complexes variously involved in the maturation process.

Keywords: Affinity purification; Mechanism; Metallocluster; Nitrogen fixation; Nitrogenase.