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Optical spectroscopic methods for probing the conformational stability of immobilised enzymes

Ganesan, A. and Moore, B.D. and Kelly, S.M. and Price, N.C. and Rolinski, O.J. and Birch, D.J.S. and Dunkin, I.R. and Halling, P.J. (2009) Optical spectroscopic methods for probing the conformational stability of immobilised enzymes. ChemPhysChem, 10 (9-10). pp. 1492-1499. ISSN 1439-4235

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    Abstract

    Structure of immobilised enzymes: Circular dichroism, infrared and fluorescence spectroscopic methods are used to characterise in situ structural stability of enzymes immobilised on particles. The enzyme subtilisin Carlsberg exhibits a similar secondary structure in solution and in the immobilised state but on the surface of porous silica gel a rigid tertiary structure is preferred. We report the development of biophysical techniques based on circular dichroism (CD), diffuse reflectance infrared Fourier transform (DRIFT) and tryptophan (Trp) fluorescence to investigate in situ the structure of enzymes immobilised on solid particles. Their applicability is demonstrated using subtilisin Carlsberg (SC) immobilised on silica gel and Candida antartica lipase B immobilised on Lewatit VP.OC 1600 (Novozyme 435). SC shows nearly identical secondary structure in solution and in the immobilised state as evident from far UV CD spectra and amide I vibration bands. Increased near UV CD intensity and reduced Trp fluorescence suggest a more rigid tertiary structure on the silica surface. After immobilised SC is inactivated, these techniques reveal: a) almost complete loss of near UV CD signal, suggesting loss of tertiary structure; b) a shift in the amide I vibrational band from 1658 cm-1 to 1632 cm-1, indicating a shift from α-helical structure to β-sheet; c) a substantial blue shift and reduced dichroism in the far UV CD, supporting a shift to β-sheet structure; d) strong increase in Trp fluorescence intensity, which reflects reduced intramolecular quenching with loss of tertiary structure; and e) major change in fluorescence lifetime distribution, confirming a substantial change in Trp environment. DRIFT measurements suggest that pressing KBr discs may perturb protein structure. With the enzyme on organic polymer it was possible to obtain near UV CD spectra free of interference by the carrier material. However, far UV CD, DRIFT and fluorescence measurements showed strong signals from the organic support. In conclusion, the spectroscopic methods described here provide structural information hitherto inaccessible, with their applicability limited by interference from, rather than the particulate nature of, the support material.

    Item type: Article
    ID code: 16940
    Keywords: circular dichroism, fluorescence spectroscopy, immobilized proteins, IR spectroscopy, protein structures, Chemistry, Atomic and Molecular Physics, and Optics, Physical and Theoretical Chemistry
    Subjects: Science > Chemistry
    Department: Faculty of Science > Pure and Applied Chemistry
    Faculty of Science > Institute of Photonics
    Faculty of Science > Physics
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      Depositing user: Strathprints Administrator
      Date Deposited: 22 Apr 2010 15:01
      Last modified: 28 Mar 2014 05:19
      URI: http://strathprints.strath.ac.uk/id/eprint/16940

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