The 2/2 hemoglobin from the cyanobacterium Synechococcus sp. PCC 7002 with covalently attached heme: comparison of X-ray and NMR structures.

The X-ray structures of the hemoglobin from Synechococcus sp. PCC 7002 (GlbN) were solved in the ferric bis-histidine (1.44 Å resolution) and cyanide-bound (2.25 Å resolution) states with covalently attached heme. The two structures illustrate the conformational changes and cavity opening caused by exogenous ligand binding. They also reveal an unusually distorted heme, ruffled as in c cytochromes. Comparison to the solution structure demonstrates the influence of crystal packing on several structural elements, whereas comparison to GlbN from Synechocystis sp. PCC 6803 shows subtle differences in heme geometries and environment. The new structures will be instrumental in elucidating GlbN reactivity.