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Plant and Cell Physiology Advance Access originally published online on October 14, 2009
Plant and Cell Physiology 2009 50(11):1898-1910; doi:10.1093/pcp/pcp134
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

The TL29 Protein is Lumen Located, Associated with PSII and Not an Ascorbate Peroxidase

Irene Granlund1,2, Patrik Storm2, Maria Schubert3, José G. García-Cerdán2, Christiane Funk2,4 and Wolfgang P. Schröder2,4,*

1Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
2Department of Biological Chemistry, Institute of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
3Department of Life Sciences, Södertörns University College, SE-141 89 Huddinge, Sweden
4Umeå Plant Science Centre (UPSC), Umeå University, SE-901 87 Umeå, Sweden

*Corresponding author: E-mail, Wolfgang.Schroder{at}chem.umu.se; Fax, +46-90-786-7661.


  Abstract

The TL29 protein is one of the more abundant proteins in the thylakoid lumen of plant chloroplasts. Based on its sequence homology to ascorbate peroxidases, but without any supporting biochemical evidence, TL29 was suggested to be involved in the plant defense system against reactive oxygen species and consequently renamed to APX4. Our in vivo and in vitro analyses failed to show any peroxidase activity associated with TL29; it bound neither heme nor ascorbate. Recombinant overexpressed TL29 had no ascorbate-dependent peroxidase activity, and various mutational analyses aiming to convert TL29 into an ascorbate peroxidase failed. Furthermore, in the thylakoid lumen no such activity could be associated with TL29 and, additionally, TL29 knock-out mutants did not show any decreased peroxidase activity or increased content of radical oxygen species when grown under light stress. Instead we could show that TL29 is a lumen-located component associated with PSII.

Keywords: APX4 • Arabidopsis • Heme • Lumen • Thylakoid membrane

Abbreviations: APX, ascorbate peroxidase; ABTS, 2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid); DIGE, differential in-gel electrophoresis; DTT, dithiothreiotol; IEF, isoelectric focusing; IPTG, isopropyl-β-D-thiogalactopyranoside; ITC, isothermal titration calorimetry; PMSF, phenylmethylsulfonyl flouride; ra, recombinant Arabidopsis; ROS, reactive oxygen species; rs, recombinant soyabean.

(Received June 29, 2009; Accepted September 29, 2009)
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