Significance of the Molecular Shape of Iron Corrphycene in a Protein Pocket

• Published in: Inorganic chemistry 2006-05, Vol.45 (10), p.4238-4242
• Main Authors: Neya, Saburo, Imai, Kiyohiro, Hiramatsu, Yoshitsugu, Kitagawa, Teizo, Hoshino, Tyuji, Hata, Masayuki, Funasaki, Noriaki
• Format: Article
• Language: English
• Subjects: Binding Sites; Ligands; Metalloporphyrins - chemical synthesis; Metalloporphyrins - chemistry; Molecular Structure; Myoglobin - chemistry; Structure-Activity Relationship
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0600679

The iron complex of a new type of corrphycene bearing two ethoxycarbonyl (−CO2C2H5) groups on the bipyrrole moiety was introduced into apomyoglobin. The reconstituted ferric myoglobin has a coordinating water molecule that deprotonates to hydroxide with a pK a value of 7.3 and exhibits 3−10-fold higher affinities for anionic ligands when compared with a counterpart myoglobin with the same substituents on the dipyrroethene moiety. In the ferrous state, the oxygen affinity of the new myoglobin was decreased to 1/410 of the native protein. The anomalies in the ligand binding, notably dependent on the side-chain location, were interpreted in terms of a characteristic core shape of corrphycene that produces the longer and shorter Fe−N(pyrrole) bonds. The spin-state equilibrium analysis of the ferric azide myoglobin containing the new iron corrphycene supported the nonequivalence of the Fe−N(pyrrole) bonds. These results demonstrate that the trapezoidal molecular shape of corrphycene exerts functional significance when the iron complex is placed in a protein pocket.