Optimization of Met8p crystals through protein-storage buffer manipulation.
Sirohaem, the prosthetic group of assimilatory sulfite and nitrite reductases, is a modified tetrapyrrole that belongs to the same fraternity of metallo-prosthetic groups as haem, chlorophyll, cobalamin and coenzyme F430 [Warren & Scott (1990), Trends Biochem Sci. 15, 486-491]. In Saccharomyces cerevisiae, the last step in the biosynthesis of sirohaem involves Met8p, a bifunctional enzyme responsible for both the NAD(+)-dependent dehydrogenation of the corrin ring and ferrochelation. Optimization of the protein storage buffer according to the results of crystallization trials resulted in a more monodisperse protein solution. Crystals were grown that diffracted to 2.1 A.