Crystal structure of a distal site double mutant of sperm whale myoglobin at 1.6 Å resolution

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Abstract
The three‐dimensional structure of sperm whale myoglobin His64(E7)→Val,Thr64(E10)→Arg double mutant has been studied by X‐ray crystallography at 1.6 Å resolution, and refined to a crystallographicR‐factor of 0.197. The Arg67(E10) side chain is extended in the direction of the ligand binding site, and its NH1 atom is at a distance of 3.11 Å from the NH1 atom of Arg45(CD3), which is also pointing towards the distal site. Both are kept in this position by hydrogen bonding and electrostatic interactions with a solvent sulfate ion, located amongst the two, on the protein surface. No liganded water molecule is present at the sixth coordination position of the Fe(III) heme.