Isolation and Characterization of a cDNA Clone Encoding a Member of the Com44/Cim44 Envelope Components of the Chloroplast Protein Import Apparatus

Ko, Kenton; Budd, David C.; Wu, Chengbiao; Seibert, Fabian S.; Kourtz, Lauralynn; Ko, Zdenka W.

doi:10.1074/jbc.270.48.28601

Cited by 64 publications

(51 citation statements)

References 40 publications

(33 reference statements)

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“…Associating proteins were detected immunologically. The anti-Tic40 IgGs used were equally immunoreactive for all Tic40 forms, independent of derivation source (yeast or plant species) (25).…”

Section: Methodsmentioning

confidence: 99%

“…Tic40 proteins were expressed using cDNAs derived from Brassica napus cv. Topas (bnToc36B, a version of Toc36 (24,25)), or Ricinus communis (rcTic40, a version of Tic40). Plastids were prepared from seedlings grown on media plates as described (32,33).…”

Section: Methodsmentioning

confidence: 99%

“…Tic40 proteins are often observed to be heterogeneous with respect to abundance, gel mobility, and different apparent configurations in the envelope (24 -27). The overall endogenous levels often display fluctuations that seem to parallel the import activity of the tissue or developmental stage (25). Tic40 components can also be found in close association with translocating proteins early in the process at the outer envelope, as well as at more advanced stages at the inner envelope (24).…”

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confidence: 99%

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Evidence That the Plastid Translocon Tic40 Components Possess Modulating Capabilities

Taylor

Argenton

et al. 2005

Journal of Biological Chemistry

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The transport of proteins into the plastid is a process that faces changing cellular needs such as the situation found in different plant organs or developing tissues. The plastid translocon must therefore be responsive to the changing cell environment to deliver efficiently different arrays of structurally diverse proteins. Although the Tic40-related envelope proteins appear to be translocon components designed to address the varying needs of protein translocation, details of their involvement remain elusive. This study was thus designed to combine plant-based experiments and yeast mitochondrion-based approaches for unveiling clues related to how the Tic40 components may behave during the protein translocation process. The main findings related to how Tic40 proteins may work are: 1) natural fluctuations are apparent in developing tissues, in different organs of the same plant, and in different species; 2) transgenic Arabidopsis seedlings can tolerate functionally a wide range of variations in Tic40 levels, from partial suppression to excessive production; 3) the Tic40 proteins themselves exhibit configurational changes in their association with yeast mitochondria in response to different carbon sources; 4) the presence of Tic40 proteins in yeast mitochondria influences regulatory aspects of the mitochondrial translocon; and 5) the Tic40 proteins associate with mitochondrial translocon components involved in regulatory-like events. The combined data provide evidence that Tic40 proteins possess modulating capabilities.Plastids are diverse in structure and function and occupy key roles in a variety of biosynthetic activities that take place in the ever changing environment of a plant cell. The role of plastids requires frequent adjustments to accommodate varying cellular needs such as those occurring in different organs, during development, during adaptation to external stimuli, or even a combination of needs. The adjustments required can be relatively subtle or distinct. The ability of the plastid to address such needs is dependent on its compositional status, e.g. chloroplasts versus leucoplasts. Although it is well established that changes to plastidial structure and function are governed predominantly by mechanisms that control gene expression (nuclear and organellar), there is growing evidence that the protein transport process contributes additionally to certain facets of these regulatory mechanisms. The involvement of protein transport in the various mechanisms of plastidial change is not unfounded because most of the plastid proteins involved are made as larger precursors before incorporation into organelles. The protein transport machinery of the plastid envelope (the plastid translocon) must therefore be accommodative in its ability to handle in an efficient manner a diverse, ever changing array of proteins. The proteins being handled range from different proteins to structural variations of the same protein.The plastid translocon is also afforded a position where additional "modulating" mechanisms can b...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Evidence That the Plastid Translocon Tic40 Components Possess Modulating Capabilities

Taylor

Argenton

et al. 2005

Journal of Biological Chemistry

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“…Tic20 has been proposed to be the inner membrane protein-conducting channel (Chen et al, 2002;Kikuchi et al, 2009). Tic40 is an inner envelope membrane protein that is found in close physical proximity to translocating precursor proteins and Tic110 (Wu et al, 1994;Ko et al, 1995;Stahl et al, 1999;Chou et al, 2006). It has a single transmembrane anchor and tetratricopeptide and stress inducible (Sti1) domains, characteristics of Hip/Hop-type cochaperones (Chou et al, 2003;Bedard et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

2010

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Heat shock protein 70s (Hsp70s) are encoded by a multigene family and are located in different cellular compartments. They have broad-ranging functions, including involvement in protein trafficking, prevention of protein aggregation, and assistance in protein folding. Hsp70s work together with their cochaperones, J domain proteins and nucleotide exchange factors (e.g., GrpEs), in a functional cycle of substrate binding and release accompanied by ATP hydrolysis. We have taken advantage of the gene targeting capability of the moss Physcomitrella patens to investigate the functions of chloroplast Hsp70s. We identified four Hsp70 genes and two GrpE cochaperone homolog genes (CGE) in moss that encode chloroplast proteins. Disruption of one of the Hsp70 genes, that for Hsp70-2, caused lethality, and protein import into heat-shocked chloroplasts isolated from temperature-sensitive hsp70-2 mutants was appreciably impaired. Whereas the double cge null mutant was not viable, we recovered a cge1 null/cge2 knock down mutant in which Hsp70-2 was upregulated. Chloroplasts isolated from this mutant demonstrated a defect in protein import. In addition, two different precursors staged as early import intermediates could be immunoprecipitated with an Hsp70-2-specific antibody. This immunoprecipitate also contained Hsp93 and Tic40, indicating that it represents a precursor still in the Toc/Tic translocon. Together, these data indicate that a stromal Hsp70 system plays a crucial role in protein import into chloroplasts.

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“…Tic40 was identified by its association with preproteins undergoing import (9,10) and is located in the inner envelope membrane in close association with Tic110 (11). Like Tic110, the bulk of Tic40 protrudes into the stroma where it may interact with stromal chaperones (12,13).…”

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confidence: 99%

Functional Similarity between the Chloroplast Translocon Component, Tic40, and the Human Co-chaperone, Hsp70-interacting Protein (Hip)

Bédard

Kubis

Bimanadham

et al. 2007

Journal of Biological Chemistry

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Tic40 is a component of the protein import apparatus of the inner envelope of chloroplasts, but its role in the import mechanism has not been clearly defined. The C terminus of Tic40 shares weak similarity with the C-terminal Sti1 domains of the mammalian Hsp70-interacting protein (Hip) and Hsp70/ Hsp90-organizing protein (Hop) co-chaperones. Additionally, Tic40 may possess a tetratricopeptide repeat (TPR) proteinprotein interaction domain, another characteristic feature of Hip/Hop co-chaperones. To investigate the functional importance of different parts of the Tic40 protein and to determine whether the homology between Tic40 and co-chaperones is functionally significant, different Tic40 deletion and Tic40:Hip fusion constructs were generated and assessed for complementation activity in the Arabidopsis Tic40 knock-out mutant, tic40. Interestingly, all Tic40 deletion constructs failed to complement tic40, indicating that each part removed is essential for Tic40 function; these included a construct lacking the Sti1-like domain (⌬Sti1), a second lacking a central region, including the putative TPR domain (⌬TPR), and a third lacking the predicted transmembrane anchor region. Moreover, the ⌬Sti1 and ⌬TPR constructs caused strong dominant-negative, albino phenotypes in tic40 transformants, indicating that the truncated Tic40 proteins interfere with the residual chloroplast protein import that occurs in tic40 plants. Remarkably, the Tic40:Hip fusion constructs showed that the Sti1 domain of human Hip is functionally equivalent to the Sti1-like region of Tic40, strongly suggesting a co-chaperone role for the Tic40 protein. Supporting this notion, yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated the in vivo interaction of Tic40 with Tic110, a protein believed to recruit stromal chaperones to protein import sites.Most chloroplast proteins are nucleus-encoded, synthesized in precursor form (each one with a cleavable transit peptide), and post-translationally imported into the organelle (1-4).Import is mediated by translocon complexes in the outer and inner envelope membranes, termed TOC 2 and TIC, respectively. Once translocation through the TOC is initiated, this complex associates with the TIC allowing preprotein transport across both membranes simultaneously. Several components of the TIC complex have been identified, including Tic40 and Tic110, but the functions of many of these proteins remain unclear (1-4). The TIC complex also recruits stromal chaperones, which are thought to drive protein import and mediate the folding of newly imported proteins (5-8).Tic40 was identified by its association with preproteins undergoing import (9, 10) and is located in the inner envelope membrane in close association with Tic110 (11). Like Tic110, the bulk of Tic40 protrudes into the stroma where it may interact with stromal chaperones (12, 13). Interestingly, Tic40 shares homology with eukaryotic Hip and Hop co-chaperones (11, 12). Weak sequence similarity between Tic40 and Hip/Hop is restricted to ...

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Isolation and Characterization of a cDNA Clone Encoding a Member of the Com44/Cim44 Envelope Components of the Chloroplast Protein Import Apparatus

Cited by 64 publications

References 40 publications

Evidence That the Plastid Translocon Tic40 Components Possess Modulating Capabilities

Evidence That the Plastid Translocon Tic40 Components Possess Modulating Capabilities

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

Functional Similarity between the Chloroplast Translocon Component, Tic40, and the Human Co-chaperone, Hsp70-interacting Protein (Hip)

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