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ATP-dependent import of a lumenal protein by isolated thylakoid vesicles

The imported protein is processed to the mature size and is resistant to digestion by proteases. The thylakoidal protein transport system is specific in that non-chloroplast proteins and precursors of stromal proteins are not imported. | The EMBO Journal vol.8 no.8 pp.2251 - 2255, 1989 ATP-dependent import of thylakoid vesicles a lumenal protein by isolated Patricia M.Kirwin, Julie W.Meadows, Jamie B.Shackleton, Janet E.Musgrove, Peter D.Elderfield, Ruth Mould, Nicole A.Hay and Colin Robinson Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK Communicated by R.J.Ellis The 33 kd protein of the photosynthetic oxygen-evolving complex is synthesized in the cytoplasm as a larger precursor and transported into the thylakoid lumen via a stromal intermediate form. In this report we describe a reconstituted system in which the later stages of this import pathway can be studied in isolation. We demonstrate inport of the 33 kd protein, probably as the intermediate form, into isolated pea thylakoids by a mechanism which is stimulated by the addition of ATP. The imported protein is processed to the mature size and is resistant to digestion by proteases. The thylakoidal protein transport system is specific in that non-chloroplast proteins and precursors of stromal proteins are not imported. Key words: chloroplast protein transport/precursor proteins/processing/thylakoid lumen proteins degree of reaction specificity (Kirwin et al., 1987, 1988). Other thylakoid lumen proteins are believed to follow a similar import pathway. For example, the 33, 23 and 16 kd proteins of the photosynthetic oxygen-evolving complex (OEC) are initially synthesized with pre-sequences which resemble that of plastocyanin in terms of overall structure: a hydrophilic, positively-charged 'envelope transfer' domain, followed by a more hydrophobic 'thylakoid transfer' domain which is thought to be involved in transfer into the thylakoids (Jansen et al., 1987; Tyagi et al., 1987). In addition, we have recently shown that precursors of the 33 and 23 kd OEC proteins are processed to the intermediate and mature sizes by the partially purified stromal and thylakoidal processing peptidases, respectively .