The Polyprotein Precursor to the Euglena Light-harvesting Chlorophyll a/b-binding Protein Is Transported to the Golgi Apparatus Prior to Chloroplast Import and Polyprotein Processing

Sulli, Chidananda; Schwartzbach, Steven D.

doi:10.1074/jbc.270.22.13084

Cited by 77 publications

(80 citation statements)

References 53 publications

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“…Proteins destined for all known secondary plastids commence their journey in the ER, but mechanisms for targeting from the ER to secondary plastids differ. In Euglenoids (green lineage), proteins are targeted to the chloroplast via the Golgi and contain a stop-transfer sequence after the transit peptide (Sulli et al, 1999;Sulli and Schwartzbach, 1995). In the case of enslaved chloroplasts derived from a red alga, CavalierSmith has suggested that proteins traffic directly from the ER (Cavalier-Smith, 2003).…”

Section: Discussionmentioning

confidence: 99%

Dissection of brefeldin A-sensitive and -insensitive steps in apicoplast protein targeting

DeRocher

Gilbert

Feagin

et al. 2005

Journal of Cell Science

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The apicoplast is a relict plastid found in many apicomplexans, including the pathogens Toxoplasma gondii and Plasmodium falciparum. Nucleus-encoded apicoplast proteins enter the ER, and after cleavage of the signal sequence, are routed to the apicoplast by virtue of a transit peptide, which is subsequently removed. To assess the mechanisms of localization we examined stable transfectants of T. gondii for the localization and processing of various GFP fusion proteins. GFP fusions bearing apicoplast targeting sequences targeted efficiently to the plastid, with no retention in the ER, even when an ER retention/retrieval sequence was added. Incubation with brefeldin A, which blocks ER-to-Golgi trafficking by inhibiting a GTP exchange factor required for retrograde trafficking, blocked the processing of the protein. Surprisingly, it did not affect the immunofluorescence pattern. To avoid the potentially misleading presence of pre-existing GFP fusion protein in the apicoplast, we used a ligand-regulated aggregation system to arrest the GFP fusion protein in the ER prior to trafficking. Upon addition of ligand to promote disaggregation, the fusion protein targeted to the plastid, even in the presence of brefeldin A. Ligand release at 15°C, which blocks trafficking of Golgirouted proteins, also allowed significant localization to the plastid. Our data indicate that apicoplast proteins can localize to the region of the plastid when Golgi trafficking is inhibited, but suggest that some steps in import or maturation of the proteins may require a brefeldin A-sensitive GTP exchange factor.

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Section: Discussionmentioning

confidence: 99%

Dissection of brefeldin A-sensitive and -insensitive steps in apicoplast protein targeting

DeRocher

Gilbert

Feagin

et al. 2005

Journal of Cell Science

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“…Presequences of nuclear-encoded plastid proteins of these organisms are also found to have a bipartite structure (38 -40). For Euglena there is evidence that precursor proteins might be translated at cytosolic ER membranes first and subsequently get transported to the plastids via the Golgi system (41,42). The general presence of N-terminal signal peptide domains in precursors of nucleus-encoded plastid proteins of cells with three-or four-membrane plastids indicates that after secondary endosymbiosis and subsequent transfer of the respective genes to the nucleus of the host cell, the pathway across the ER membranes was utilized to target proteins into the newly acquired plastids.…”

Section: Discussionmentioning

confidence: 99%

Protein Transport into “Complex” Diatom Plastids Utilizes Two Different Targeting Signals

Lang

Apt²,

Kroth

1998

Journal of Biological Chemistry

104

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The plastids found in diatoms and other chromophytic algae are completely enclosed by four membranes in contrast to chloroplasts of higher plants, which are surrounded by only two membranes. The bipartite targeting sequence of diatom nuclear-encoded plastid proteins contains an endoplasmic reticulum signal sequence and, based on sequence comparison, a transit peptide-like domain similar to that which targets proteins into the plastids of higher plants. By performing heterologous import experiments using the precursor of the ␥ subunit of the chloroplast ATPase from the diatom Odontella sinensis we were able to show that protein import into diatom plastids is at least a two-step event. We demonstrate that the first step involves co-translational transport through endoplasmic reticulum membranes and that there is an additional targeting step which is similar to the import of precursor proteins into chloroplasts of higher plants and green algae indicating that the transit peptide-like domain of the diatom precursor is functionally equivalent to the respective targeting signal of higher plants. Our results suggest that the transit peptide depending targeting mechanism in plastids has apparently remained relatively unchanged over the course of evolution, with only the peptidase cleavage site significantly modified.

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“…pLHCPll is synthesized on membrane-bound polysomes (Kishore and Schwartzbach, 1992), and immunoelectron microscopy localizes LHCPll to the Golgi apparatus before LHCPll accumulation in thylakoids Schiff et al, 1991). In vivo pulse-chase experiments have shown that pLHCPll is transported as a membrane-bound polyprotein from the ER to the Golgi apparatus and from the Golgi apparatus to the chloroplast (Sulli and Schwartzbach, 1995).…”

Section: Introductionmentioning

confidence: 99%

A soluble protein is imported into Euglena chloroplasts as a membrane-bound precursor.

Sulli

Schwartzbach

1996

Plant Cell

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The Euglena precursor to the small subunit of ribulose-1,Bbisphosphate carboxylase/oxygenase (pSSU) is a polyprotein. To determine the transport route from cytoplasm to chloroplast, Euglena was pulse labeled with 35S-sulfate and the organelles were separated on sucrose gradients. After a pulse, pSSU was found in the endoplasmic reticulum (ER) and Golgi apparatus. During a chase, ER-and Golgi-localized pSSU decreased concomitant with the appearance of SSU in chloroplasts. SSU was not found in pSSU-containing ER and Golgi fractions. Na2C03 did not remove pSSU from ER or Golgi membranes, indicating that it was an integral membrane protein. pSSU was inserted in vitro into canine microsomes, and Na2C03 did not remove pSSU from the microsomal membrane. The in vivo and in vitro experiments show that Euglena pSSU is inserted into the ER membrane and transported as an integral membrane protein to the Golgi apparatus before chloroplast import and polyprotein processing.

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The Polyprotein Precursor to the Euglena Light-harvesting Chlorophyll a/b-binding Protein Is Transported to the Golgi Apparatus Prior to Chloroplast Import and Polyprotein Processing

Cited by 77 publications

References 53 publications

Dissection of brefeldin A-sensitive and -insensitive steps in apicoplast protein targeting

Dissection of brefeldin A-sensitive and -insensitive steps in apicoplast protein targeting

Protein Transport into “Complex” Diatom Plastids Utilizes Two Different Targeting Signals

A soluble protein is imported into Euglena chloroplasts as a membrane-bound precursor.

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