Structure and ligand binding properties of myoglobins reconstituted with monodepropionated heme: functional role of each heme propionate side chain.
Two heme propionate side chains, which are attached at the 6 and 7 positions of the heme framework, are linked with Arg45 and Ser92, respectively, in sperm whale myoglobin. To evaluate the role of each propionate, two kinds of one-legged hemins, 6-depropionated and 7-depropionated protohemins, were prepared and inserted into the apomyoglobin to yield two reconstituted proteins. Structural data of the reconstituted myoglobins were obtained via an X-ray crystallographic analysis at a resolution of 1.1-1.4 A and resonance Raman spectroscopy. It was found that the lack of the 6-propionate reduces the number of hydrogen bonds in the distal site and clearly changes the position of the Arg45 residue with the disrupting Arg45-Asp60 interaction. In contrast, the removal of the 7-propionate does not cause a significant structural change in the residues of the distal and proximal sites. However, the resonance Raman studies suggested that the coordination bond strength of the His93-Fe bond for the protein with the 7-depropionated protoheme slightly increases compared to that for the protein with the native heme. The O2 and CO ligand binding studies for the reconstituted proteins with the one-legged hemes provide an important insight into the functional role of each propionate. The lack of the 6-propionate accelerates the O2 dissociation by ca. 3-fold compared to those of the other reconstituted and native proteins. The lack of the 7-propionate enhances the CO affinity by 2-fold compared to that of the protein with the native heme. These results indicate that the 6-propionate clearly contributes to the stabilization of the bound O2, whereas the 7-propionate plays an important role in the regulation of the Fe-His bond.
Harada
Katsuyoshi
K
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan.
Makino
Masatomo
M
Sugimoto
Hiroshi
H
Hirota
Shun
S
Matsuo
Takashi
T
Shiro
Yoshitsugu
Y
Hisaeda
Yoshio
Y
Hayashi
Takashi
T
D000595:Amino Acid Sequence; D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry; D018360:Crystallography, X-Ray; D006418:Heme / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008786:Metmyoglobin / Q000737:chemistry*; D008969:Molecular Sequence Data; D009211:Myoglobin / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D011422:Propionates / Q000737:chemistry*; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
D008024:Ligands; D009211:Myoglobin; D011422:Propionates; C055547:deoxymyoglobin; D008786:Metmyoglobin; D006418:Heme; D002248:Carbon Monoxide; D007501:Iron; D010100:Oxygen