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

AbstractThe 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 crystallographic R-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