The heme iron coordination complex in His64(E7)Tyr recombinant sperm whale myoglobin.
By using site-directed mutagenesis of recombinant sperm whale (SW) myoglobin, the native distal histidine residue, at position 64 (the helical position E7), has been replaced with a tyrosine. The mutation of His64Tyr SW myoglobin has an analogous heme iron electronic structure as that of native hemoglobins M Boston and M Saskatoon. Optical spectroscopy showed that the distal tyrosine bound to the heme iron had a pK value of 5.6. In the pH range of 4.7-11.0, electron spin resonance spectroscopy suggested the presence of two heme iron ligation schemes: the heme iron bound to a distal water molecule or to a distal tyrosine residue. The heme iron coordination in the wild-type myoglobin and in the His64Tyr SW Mb mutant was studied by X-ray absorption near-edge structure (XANES) spectroscopy. Indeed, the heme iron K-edge reflects the electronic organization of the metal inside the six-coordinated complex. Comparative analysis of X-ray absorption heme iron K-edge shapes showed that the heme iron of His64Tyr SW myoglobin is bound to the oxygen atom from the phenol group of the distal tyrosine residue (Fe-OH phi). When the pH value decreased from pH 7 to 5.6, the Fe-OH phi bond strength decreased, resulting in an increase of the heme iron high-spin population of His64Tyr SW myoglobin. At low pH values, the Fe-OH phi bond can be disrupted with the possibility of heme iron binding of another ligand having a higher affinity.(ABSTRACT TRUNCATED AT 250 WORDS)
Pin
S
S
Laboratoire de Biologie Physico-Chimique, Université Paris VII, France.
Alpert
B
B
Cortès
R
R
Ascone
I
I
Chiu
M L
ML
Sligar
S G
SG
D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009211:Myoglobin / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry; D013053:Spectrophotometry; D013057:Spectrum Analysis; D014907:Whales
D009211:Myoglobin; D011994:Recombinant Proteins; C089624:myoglobin, His(64)Tyr-; D006418:Heme; D007501:Iron