The contribution of ionic interactions to the conformational stability and function of polygalacturonase from A. niger.

Jyothi, T. C. and Sridevi Annapurna, Singh and Appu Rao, A. G. (2005) The contribution of ionic interactions to the conformational stability and function of polygalacturonase from A. niger. International Journal of Biological Macromolecules, 36 (5). pp. 310-7. ISSN 0141-8130

PDF International Journal of Biological Macromolecules, Volume 36, Issue 5, 28 September 2005, Pages 310-317.pdf - Published Version Restricted to Registered users only Download (183kB)

Abstract

Aspergillus niger produces multiple forms of polygalacturonases with molecular masses ranging from 30 to 60 kDa. The high molecular weight polygalacturonase (61+/-2 kDa) from A. niger possesses a pH optimum of 4.3 and a pI of 3.9. The enzyme exhibited high sensitivity, both in terms of activity and structure, in the pH range of 4.3-7.0. The enzyme was irreversibly inactivated at pH 7.0. The enzyme is predominantly rich in parallel beta structure. There is unfolding of the enzyme molecule between 4.3 and 7.0 resulting in irreversible loss of secondary and tertiary structure with the exposure of hydrophobic surfaces. ANS binding measurements, intrinsic fluorescence and acrylamide quenching measurements have confirmed the unfolding and exposure of hydrophobic surfaces. The midpoint of pH transition for both activity and secondary structure is 6.2+/-0.1. The pH-induced changes of polygalacturonase confirm the role of histidine residues in structure and activity of the enzyme. The irreversible nature of inactivation is due to the unfolding induced exposure of hydrophobic surfaces leading to association/aggregation of the molecule. Size exclusion chromatography measurements have established the association of enzyme at higher pH. Urea induced unfolding measurements at pH 4.3 and 7.0 have confirmed the loss in stability as we approach neutral pH.

Item Type:	Article
Uncontrolled Keywords:	A. niger; Conformational change; Histidine residues; Ionic interactions; Polygalacturonase
Subjects:	500 Natural Sciences and Mathematics > 07 Life Sciences > 04 Microbiology > 04 Fungi 600 Technology > 08 Food technology > 16 Nutritive value > 05 Enzymes
Divisions:	Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	30 Jun 2017 05:27
Last Modified:	30 Jun 2017 05:27
URI:	http://ir.cftri.res.in/id/eprint/1978

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