| 1. |
- Forsberg, Jens, et al.
(författare)
-
Protease activities in the chloroplast capable of cleaving an LHCII N-terminal peptide
- 2005
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 123:1, s. 21-29
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Halbhuber, Z, et al.
(författare)
-
Overexpression and purification of recombinant membrane PsbH protein in Escherichia coli.
- 2003
-
Ingår i: Protein Expression and Purification. - 1046-5928. ; 32:1, s. 18-27
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we featured an expression system that enables the production of sufficient quantities (~mg) of low molecular weight membrane protein of photosystem II, PsbH protein, for solid-state NMR as well as other biophysical studies. PsbH gene from cyanobacterium Synechocystis sp. PCC 6803 was cloned into a plasmid expression vector, which allowed expression of the PsbH protein as a glutathione-S transferase (GST) fusion protein in Escherichia coli BL21(DE3) cells. A relatively large GST anchor overcomes foreseeable problems with the low solubility of membrane proteins and the toxicity caused by protein incorporation into the membrane of the host organism. As a result, the majority of fusion protein was obtained in a soluble state and could be purified from crude bacterial lysate by affinity chromatography on immobilized glutathione under non-denaturing conditions. The PsbH protein was cleaved from the carrier protein with Factor Xa protease and purified on DEAE–cellulose column with yields of up to 2.1 g protein/ml of bacterial culture. The procedure as we optimized is applicable for isolation of small membrane proteins for structural studies.
|
|
