Significance of the molecular shape of iron corrphycene in a protein pocket.
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.
Neya
Saburo
S
Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, Inage-Yayoi, Chiba 263-8522, Japan. sneya@p.chiba-u.ac.jp
Imai
Kiyohiro
K
Hiramatsu
Yoshitsugu
Y
Kitagawa
Teizo
T
Hoshino
Tyuji
T
Hata
Masayuki
M
Funasaki
Noriaki
N