Incorporation of a Phebox Rhodium Complex into apo-Myoglobin Affords a Stable Organometallic Protein Showing Unprecedented Arrangement of the Complex in the Cavity

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• 作者：Yuh Satake ; Satoshi Abe ; Seiji Okazaki ; Noritaka Ban ; Tatsuo Hikage ; Takafumi Ueno ; Hiroshi Nakajima ; Atsuo Suzuki ; Takashi Yamane ; Hisao Nishiyama ; Yoshihito Watanabe
• 刊名：Organometallics
• 出版年：2007
• 出版时间：September 24, 2007
• 年：2007
• 卷：26
• 期：20
• 页码：4904 - 4908
• 全文大小：232K
• 年卷期：v.26,no.20(September 24, 2007)
• ISSN：1520-6041

文摘

Novel organometallic proteins have been synthesized as a 1:1 composite of rhodium 2,6-bis(2-oxazolinyl)phenyl (Rh·Phebox) complexes with the apo-form of myoglobin, which is an oxygen-transportprotein having b-type heme (iron porphyrin IX) as a natural prosthetic group. The X-ray structural analysisreveals that the Rh·Phebox complex with phenyl substituents is included in the cavity with an almostperpendicular arrangement to that of the heme. The unique arrangement is supported by hydrogen bondingand a number of hydrophobic interactions, especially - interactions between the phenyl rings of thesubstituents and the imidazole moiety of His93, which is a ligand of the rhodium atom. Semiquantitativeanalysis of the composite stability by ESI mass spectroscopy clearly indicates that the stability of thecomposites depends on an extent of the interaction between the substituents of the Rh·Phebox complexesand His93. Enantioselectivity for the chiral (S,S)- and (R,R)-Rh·Phebox complexes with the phenylsubstituents is also observed in terms of the difference in the stability of the composites. According tothe arrangement of the amino acid residues around the Phebox ligand, the (S,S)-form has a suitableconfiguration to fit one of its phenyl rings into the hollow formed by Leu89, His93, and Ile99, whilestructural distortion will result if the (R,R)-isomer adopts an arrangement similar to that of the (S,S)-isomer, which is confirmed with the enhancement of the maximal and minimal ellipticities of the circulardichroic spectrum in comparison with that of the intact (R,R)-isomer. Such structural strain would reducethe efficient - interaction between the ligand substituents and His93, resulting in less stability of thecomposite containing the (R,R)-isomer. The results obtained here demonstrate that the myoglobin cavityis capable of accommodating organometallic compounds totally different from the heme in its molecularshape and the arrangement in the cavity. The extension and application of the present method will allowus to produce artificial organometallic proteins bearing functions that are difficult to achieve with naturalprosthetic groups.