Tat‐dependent targeting of Rieske iron‐sulphur proteins to both the plasma and thylakoid membranes in the cyanobacterium Synechocystis PCC6803

Abstract

SummaryCyanobacteria possess a differentiated membrane system and transport proteins into both the periplasm and thylakoid lumen. We have used green fluorescent protein (GFP)-tagged constructs to study the Tat protein transporter and Rieske Tat substrates in Synechocystis PCC6803. The Tat system has been shown to operate in the plasma membrane; we show here that it is also relatively abundant in the thylakoid membrane network, indicating that newly synthesized Tat substrates are targeted to both membrane systems. Synechocystis contains three Rieske ironsulphur proteins, all of which contain typical twinarginine signal-like sequences at their N-termini. We show that two of these proteins (PetC1 and PetC2) are obligate Tat substrates when expressed in Escherichia coli. The Rieske proteins exhibit differential localization in Synechocystis 6803; PetC1 and PetC2 are located in the thylakoid membrane, while PetC3 is primarily targeted to the plasma membrane. The combined data show that Tat substrates are directed with high precision to both membrane systems in this cyanobacterium, raising the question of how, and when, intracellular sorting to the correct membrane is achieved.

Plant mitochondria contain the protein translocase subunits TatB and TatC

“…This is fully consistent with our observations that mutation of the AtRip Tat targeting signal and also that AtRip requires a ΔpH for assembly. Rip proteins of chloroplasts and bacteria have also been demonstrated previously to require a Tat pathway for proper insertion (Molik et al, 2001;Aldridge et al, 2008;Bachmann et al, 2006;De Buck et al, 2007). These observations are strengthened by the correlation of mitochondrial Tat proteins with the absence of a complete Bcs1 protein in a variety of organisms.…”

Multiple Rieske Proteins Enable Short- and Long-term Light Adaptation of Synechocystis sp. PCC 6803

“…All this might indicate a function of PetC3 that is different from the other two isoforms. In agreement with this, PetC3 was recently reported to be located exclusively in the cytoplasmic membrane of Synechocystis (55,60). Also, as the ⌬petC1/2 double deletion strain does not survive (40), PetC3 apparently cannot functionally substitute PetC1, and the determined midpoint redox potential (ϩ135 mV) is too negative to allow PetC3 to be a component of the linear electron transport chain (41).…”

Deletion of Synechocystis sp. PCC 6803 Leader Peptidase LepB1 Affects Photosynthetic Complexes and Respiration

“…Though relatively little is still known about respiration in PM (64), CtaII was found only in this subfraction (7,24,46,48,65) and CydAB in both TM and PM (45,48). The Rieske protein PetC3, which was found to increase in the mutant as seen in Western blot and iTRAQ analyses, was shown to be present only in PM (64) and, similarly, a GFP-PetC3 construct was targeted to PM (66). Because of its unusually low redox potential (ϩ135 mV), PetC3 cannot be a component of the "classical" Cyt b 6 f complex and oxidize plastoquinone (60).…”