Protease activities in the chloroplast capable of cleaving an LHCII N-terminal peptide

Summary, in English

Two protease activities of pea chloroplasts, one located in the stroma and the other associated to the thylakoid membrane, are described. Both proteases catalyse the endo-proteolytic cleavage of a peptide corresponding to the N-terminal loop and the first turn in helix-B of light-harvesting complex II (Lhcb1 from pea). The stromal protease cleaves preferentially on the carboxy-side of glutamic acid residues. Inhibitor studies indicate that this protease is a serine-type protease. The protease was partially purified and could be correlated to a 95-kDa polypeptide band on SDS-polyacrylamide gels. The 95 kDa protein was partially sequenced and showed similarity to an to an 'unknown protein' from A. thaliana (in the NCBI public database) as well as to a glutamyl endopeptidase purified from crude extract of cucumber leaves. It is concluded that the stromal protease is a chloroplast glutamyl endopeptidase (cGEP). The protease localized in the thylakoid membrane, cleaved the peptide at only one site, close to its N terminus. The activity of the thylakoid-associated protease was found to be drastically increased in the presence of the reducing agent 1,4-dithiothreitol. Inhibitor studies suggest that this protease is a cysteine- or serine-type protease. The possible roles of these proteases in the regulation of photosynthetic electron transport and in the chloroplast homeostasis are discussed.

• Författare: Jens Forsberg; Jörgen Ström; T Kieselbach; H Larsson; K Alexciev; A Engstrom; Hans-Erik Åkerlund
• Avdelning/ar: Biokemi och Strukturbiologi
• Publiceringsår: 2005
• Språk: Engelska
• Sidor: 21-29
• Publikation/Tidskrift/Serie: Physiologia Plantarum
• Volym: 123
• Issue: 1
• Länkar: http://dx.doi.org/10.1111/j.1399-3054.2005.00441.x
• Dokumenttyp: Artikel i tidskrift
• Förlag: John Wiley & Sons Inc.
• Ämne: Biological Sciences
• Status: Published
• ISBN/ISSN/Övrigt: ISSN: 0031-9317