Role of histidines in the binding of violaxanthin de-epoxidase to the thylakoid membrane as studied by site-directed mutagenesis
Author
Summary, in English
Regulation of violaxanthin de-epoxidase (VDE) involves a conformational change at low lumenal pH, followed by binding of the enzyme to the thylakoid membrane. The role of histidine residues in this process was studied by release of unbound enzyme from thylakoids upon sonication, on a pH scale from 4.7 to 7.1. The co-operativity for binding of spinach VDE (four histidines) to the membrane was found to be 3.8, with respect to protons, and had an inflexion point at pH 6.6, whereas VDE from wheat (three histidines) showed a co-operativity of 2.9 and had an inflexion point at pH 6.2. Mutant forms of VDE were constructed and probed for their binding to the outside of thylakoid membranes. With one or two histidines substituted for alanine or arginine, a lower co-operativity (1.6-2.3) was found, compared with the wild type. Based on these findings, and that the pKa value for histidine is within the range where the VDE binding takes place, we propose that protonation of the histidine residues at low pH induces the conformational change of VDE, and hence indirectly regulates binding of the enzyme to the thylakoid membrane.
Department/s
Publishing year
2004
Language
English
Pages
337-343
Publication/Series
Physiologia Plantarum
Volume
122
Issue
3
Links
Document type
Journal article
Publisher
John Wiley & Sons Inc.
Topic
- Biological Sciences
Status
Published
ISBN/ISSN/Other
- ISSN: 0031-9317