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PEDS Advance Access published online on February 1, 2006
Protein Engineering Design and Selection, doi:10.1093/protein/gzj016
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received July 23, 2005
Revised September 17, 2005
Accepted January 3, 2006

Article

Increased thermal and organic solvent tolerance of modified horseradish peroxidase

Jian-Zhong Liu 1 *, Teng-Li Wang 1, Ming-Tao Huang 1, Hai-Yan Song 1, Li-Ping Weng 1, and Liang-Nian Ji 1

1 Biotechnology Research Center and Key Laboratory of Gene Engineering of Ministry of Education, State Key Laboratory of Biocontrol, Zhongshan University, Guangzhou 510275, P.R.China

* To whom correspondence should be addressed.
Jian-Zhong Liu, E-mail: lssljz{at}zsu.edu.cn


  Abstract

Horseradish peroxidase (HRP) was modified by maleic anhydride and citraconic anhydride. The thermal and organic solvent tolerances of native and modified enzyme were compared. These chemical modifications of HRP increased their thermostability both in aqueous buffer and some organic solvents, and also enhanced their tolerances of some organic solvents. We have studied the unfolding of native and modified HRP by heat to determine the conformational stability. The temperature at the midpoint of thermal denaturation (Tm) was increased upon modification. Both enthalpy change ({Delta}Hm) and entropy change ({Delta}Sm) for unfolding of modified enzyme at Tm were decreased compared with native enzyme. Circular dichroism studies proved that these modifications changed the conformation of HRP. The improvements of stability are related to side chain reorientations of aromatics upon both modifications.

Keywords: chemical modification; horseradish peroxidase; organic solvent; thermostability.
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