Journal of Protein Chemistry

, Volume 9, Issue 5, pp 641–646 | Cite as

Role of a disulfide cross-link in the conformational stability of a thermostable xylanase

  • Utpal Tatu
  • S. K. Murthy
  • P. J. Vithayathil


The role of a S-S cross-link in the conformational stability of xylanase fromHumicola lanuginosa has been investigated using CD, UV absorption spectroscopy, and RIA displacement studies. Our studies show that reduction and carboxymethylation of the S-S cross-link in xylanase results in a gross conformational perturbation of the protein. The secondary structure analysis of the CD spectra indicates that the xylanase with an intact S-S contains 66% β-sheet structure and remaining random coil. Cleavage of the S-S bond results in a loss of 25% β-sheet structure. Thermal denaturation studies using CD spectroscopy andpH-dependent tyrosine ionization studies using UV spectroscopy show that the presence of disulfide cross-link offers resistance against unfolding by extremes of temperature andpH. Further, we demonstrate that the heat-induced changes in xylanase with intact S-S bond are almost totally reversible, while those in the S-S cleaved enzyme fail to show any significant reversal. Our studies support the present theory that S-S cross-links exert their stabilizing effect in proteins by destabilizing the unfolded state of the protein and forcing it back to a more folded state.

Key words

CD disulfide bond protein stability RIA secondary structure tyrosine ionization xylanase 


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Copyright information

© Plenum Publishing Corporation 1990

Authors and Affiliations

  • Utpal Tatu
    • 1
  • S. K. Murthy
    • 1
  • P. J. Vithayathil
    • 1
  1. 1.Department of BiochemistryIndian Institute of ScienceBangaloreIndia

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