Organophosphorus Hydrolase at the Air-Water Interface: Secondary Structure and Interaction with Paraoxon
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- 作者：Jiayin Zheng ; Bernard Desbat ; Vipin K. Rastogi ; Saumil S. Shah ; Joseph J. DeFrank ; Roger M. Leblanc
- 刊名：Biomacromolecules
- 出版年：2006
- 出版时间：October 2006
- 年：2006
- 卷：7
- 期：10
- 页码：2806 - 2810
- 全文大小：341K
- 年卷期：v.7,no.10(October 2006)
- ISSN：1526-4602
文摘
The secondary structure of organophosphorus hydrolase (OPH) at the air-water interface was studied usingpolarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The shape and position of theamide I and amide II bands were used to estimate the surface conformation and orientation of OPH. The PM-IRRAS results indicated that the enzyme did not unfold for the range of surface pressure used (0-30 mN/m). Atlow surface pressures, the signal of amide I was very weak and the intensity was almost the same as amide II.Upon further compression, the PM-IRRAS signal and the ratio of the intensity of amide I and amide II bothincrease, implying an increased interfacial concentration of the enzyme. From the amide I/amide II ratio and theband position, it was deduced that the enzyme adopts a conformation which gives a higher occupied surface atlow surface pressure and rotates to a more vertical orientation at high surface pressures. The compression anddecompression of the OPH monolayer indicated that the fingerprint of the secondary structure at the air-waterinterface was reversible. PM-IRRAS was also used to investigate the pH effect of the subphase on the secondarystructure of OPH. The secondary structure of OPH at the air-water interface was well defined when the pH ofthe subphase was near its isoelectric point (IP, pH 7.6). However, it adopted a different orientation when thesubphase pH values were higher or lower than the IP with formation of random coil structure. The hydrolysis oforganophosphorus compound paraoxon by OPH was also studied at the air-water interface by PM-IRRAS. ThepH effect and the interaction with paraoxon both seem to orientate the enzyme more in the plane of the interfaceand to produce random coil structure.