Heme Recognition and Transmembrane Allostery
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An amphiphilic imidazolyl protoporphyrin IX
have been synthesized by attaching 1'-[2-(2-(2-amino ethoxy) ethoxy) ethoxy]-12'-(imidazol-1-yl)-dodecane
to one of the two propionic groups of protoporphyrin IX. The resulting
porphyrin, H2AmImPPIX, and the metallo-derivatives, MAmImPPIX
(M= Fe(III), Zn(II)), could be incorporated into phospholipid model membrane
in a highly controlled manner, with the protoporphyrin IX head group positioned
on the water-lipid interface and the amphiphilic tail inserted into the
lipid bilayer. Langmuir-Blodgett studies suggested that the porphyrin planes
of H2AmImPPIX and MAmImPPIX were mostly likely paralell to the
membrane plane. Addion of Fe(III)AmImPPIX to the outer leaflet of DPPC
(dipalmitoylphosphatidylcholine) vesicle containing the zinc steroidal
porphyrin, Zn(ChP), resulted in the formation of a binary porphyrin membrane
system, in which the two porphyrin had their macrocyclic plane paralell
to each other and tethered by the ligation bond between the terminal imidazole
of Fe(III)AmImPPIX and the metal center of Zn(ChP) at the middle of the
lipid bilayer. This binary porphyrin unit could serve as a signaling receptor
for the recognition of a external signaling macromolecule, apomyoglobin.
Upon binding of apomyoglobin to the protoporphyrin head group of the Fe(III)AmImPPIX
on the membrane surface, the ligation bond at the center of the membrane
was allosterically cleaved, which resulted in the recovery of the Zn(ChP)
fluorescence signal. |
