title: Thylakoid targeting of Tat passenger proteins shows no delta pH dependence in vivo.
abstract: The Tat pathway is a major route for protein export in prokaryotes and for protein targeting to thylakoids in chloroplasts. Based on in vitro studies, protein translocation through this pathway is thought to be strictly dependent on a transmembrane delta pH. In this paper, we assess the delta pH sensitivity of the Tat pathway in vivo. Using Chlamydomonas reinhardtii, we observed changes in the efficiency of thylakoid targeting in vivo by mutating the Tat signal of the Rieske protein. We then employed two endogenous pH probes located on the lumen side of the thylakoid membranes to estimate spectroscopically the delta pH in vivo. Using experimental conditions in which the trans-thylakoid delta pH was almost zero, we found no evidence for a delta pH dependence of the Tat pathway in vivo. We confirmed this observation in higher plants using attached barley leaves. We conclude that the Tat pathway does not require a delta pH under physiological conditions, but becomes delta pH sensitive when probed in vitro/in organello because of the loss of some critical intracellular factors.
authors.affiliation: Physiologie Membranaire et Moléculaire du Chloroplaste CNRS UPR1261, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
authors.forename: Claudia
authors.initials: C
authors.lastname: Chasen
authors.forename: Francis-André
authors.initials: FA
authors.lastname: Wollman
authors.forename: Catherine
authors.initials: C
authors.lastname: de Vitry
mesh_terms: D000818:Animals; D029681:Arabidopsis Proteins; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D003573:Cytochrome b Group / Q000235:genetics* / Q000378:metabolism; D045346:Cytochrome b6f Complex; D001467:Hordeum / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D009154:Mutation; D009550:Nigericin / Q000494:pharmacology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D021382:Protein Sorting Signals / Q000235:genetics* / Q000502:physiology; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D003573:Cytochrome b Group; D007476:Ionophores; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D021382:Protein Sorting Signals; C121497:psbQ protein, Arabidopsis; D045346:Cytochrome b6f Complex; D009550:Nigericin