Proteome Map of the Chloroplast Lumen of Arabidopsis thaliana
The thylakoid membrane of the chloroplast is the cen- ter of oxygenic photosynthesis. To better understand the function of the luminal compartment within the thy- lakoid network, we have carried out a systematic char- acterization of the luminal thylakoid proteins from the model organism Arabidopsis thaliana. Our data show that the thylakoid lumen has its own specific proteome, of which 36 proteins were identified. Besides a large group of peptidyl-prolyl cis-trans isomerases and pro- teases, a family of novel PsbP domain proteins was found. An analysis of the luminal signal peptides showed that 19 of 36 luminal precursors were marked by a twin-arginine motif for import via the Tat pathway. To compare the model organism Arabidopsis with another typical higher plant, we investigated the proteome from the thylakoid lumen of spinach and found that the lumi- nal proteins from both plants corresponded well. As a complement to our experimental investigation, we made a theoretical prediction of the luminal proteins from the whole Arabidopsis genome and estimated that the thy- lakoid lumen of the chloroplast contains 80 proteins.