The Endoplasmic Reticulum: Gateway of the Secretory Pathway

Vitale, Alessandro; Denecke, Jürgen

doi:10.2307/3870888

Cited by 110 publications

(148 citation statements)

References 40 publications

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“…2) and PDI (data not shown) in ricinosomes was also demonstrated by Western blotting. Analysis of the sucrose gradient fractions revealed a strong signal with ␣-BiP antibodies in the upper part of the gradient (around fractions [4][5][6][7], where the ER is found, a weaker signal in the middle of the gradient (fractions [16][17][18][19], and again a peak where ricinosomes are found (fractions 22-24). As controls, gMDH and mMDH were used and did not react with fractions containing ricinosomes.…”

Section: The Er Resident Proteins Bip (Hsp70) and Pdi Are Found Withinmentioning

confidence: 99%

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The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum

Schmid

Simpson

Sarioglu

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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The ricinosome (synonym, precursor protease vesicle) is a novel organelle, found so far exclusively in plant cells. Electron microscopic studies suggest that it buds off from the endoplasmic reticulum in senescing tissues. Biochemical support for this unusual origin now comes from the composition of the purified organelle, which contains large amounts of a 45-kDa cysteine endoprotease precursor with a C-terminal KDEL motif and the endoplasmic reticulum lumen residents BiP (binding protein) and protein disulfide isomerase. Western blot analysis, peptide sequencing, and mass spectrometry demonstrate retention of KDEL in the protease proform. Acidification of isolated ricinosomes causes castor bean cysteine endopeptidase activation, with cleavage of the N-terminal propeptide and the C-terminal KDEL motif. We propose that ricinosomes accumulate during senescence by programmed cell death and are activated by release of protons from acidic vacuoles.Ricinus communis ͉ papain-type KDEL peptidase P rogrammed cell death (PCD) in higher plants and animals fulfills multiple functions in the differentiation or turnover of tissues and is triggered by pathogens at and around the site of infection as a mechanism to prevent proliferation of the disease (1, 2). Examples for elimination by PCD of organs that serve temporary functions are tadpole tails during metamorphosis and the endosperm of the castor bean during germination. In plants, the PCD of whole organs such as leaves, flowers, and fruits is designated as senescence (3).Biochemical pathways accompanying PCD or apoptosis in mammals have been elucidated in detail (reviewed in ref. 4). Plant cells undergoing senescence by PCD express papain-type cysteine endoproteases with a C-terminal KDEL sequence (5). They attract attention because they are present in the senescing endosperm cells of castor bean (Ricinus communis) as relatively inactive 45-kDa proenzymes until the final stages of PCD, at which time they are processed into the 35-kDa mature form with a 50-100 times higher activity (6).The cysteine endopeptidase from senescing castor bean endosperm (CysEP) is homologous to papain-type KDEL cysteine endopeptidases from senescing flower petals of daylily, the maturing French bean pods, and the cotyledons of germinating mung bean and vetch (6). In castor bean, daylily, and mung bean, the KDEL-tailed propeptidase is stored in a special organelle, called ricinosome (5, 6) or KDEL-tailed cysteine proteinaseaccumulating vesicles (KV) (7). Ricinosomes were first described and ultrastructurally characterized in the endosperm of R. communis (8, 9), whereas KV were described as cytoplasmic ''foci'' in Vigna radiata (10). The mature CysEP was originally purified from germinating castor bean endosperm (11). Sequencing of cDNA clones from the endosperm of germinating seedlings and from developing seeds established the presence of a presequence for cotranslational targeting into the lumen of the endoplasmic reticulum (ER), an N-terminal propeptide and a C-terminal KDEL motif. Immunogold l...

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Section: The Er Resident Proteins Bip (Hsp70) and Pdi Are Found Withinmentioning

confidence: 99%

“…The C-terminal KDEL motif functions as a Golgi retrieval signal for the 5% escaping ER lumen proteins (16). In terms of ricinosome biogenesis, it is relevant if ricinosomal proCysEP retains its C-terminal KDEL motif, thus indicating a direct development of ricinosomes from the ER.…”

Section: The Proform Of the Cysep In Ricinosomes Retains The C-terminmentioning

confidence: 99%

The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum

Schmid

Simpson

Sarioglu

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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“…This protein may be present in a different subdomain of the ER than the proteins in the training and test sets. ER membrane proteins continuously escape from the ER to the Golgi and are retrieved in retrograde vesicles (17). The magnitude of the ribophorin I Golgi score could therefore reflect the steady state distribution of this protein, with the majority resident in the ER and a minority in the Golgi awaiting retrieval.…”

Section: Namementioning

confidence: 99%

Localization of Organelle Proteins by Isotope Tagging (LOPIT)

Dunkley

Watson

Griffin

et al. 2004

Molecular & Cellular Proteomics

319

298

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We describe a proteomics method for determining the subcellular localization of membrane proteins. Organelles are partially separated using centrifugation through selfgenerating density gradients. Proteins from each organelle co-fractionate and therefore exhibit similar distributions in the gradient. Protein distributions can be determined through a series of pair-wise comparisons of gradient fractions, using cleavable ICAT to enable relative quantitation of protein levels by MS. The localization of novel proteins is determined using multivariate data analysis techniques to match their distributions to those of proteins that are known to reside in specific organelles. Using this approach, we have simultaneously demonstrated the localization of membrane proteins in both the endoplasmic reticulum and the Golgi apparatus in Arabidopsis. Localization of organelle proteins by isotope tagging is a new tool for high-throughput protein localization, which is applicable to a wide range of research areas such as the study of organelle function and protein trafficking.

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“…BiP is a major chaperone of the ER (Vitale and Denecke, 1999). BiP transiently binds many newly synthesized secretory proteins and most probably prevents unspecific aggregation by interacting with regions rich in hydrophobic amino acids; such regions are exposed in folding and assembly intermediates but not in structurally mature proteins, which are therefore permanently released from the chaperone.…”

Section: Zeolin Extensively Interacts With Bip But Is Very Stablementioning

confidence: 99%

Zeolin. A New Recombinant Storage Protein Constructed Using Maize γ-Zein and Bean Phaseolin

et al. 2004

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The major seed storage proteins of maize (Zea mays) and bean (Phaseolus vulgaris), zein and phaseolin, accumulate in the endoplasmic reticulum (ER) and in storage vacuoles, respectively. We show here that a chimeric protein composed of phaseolin and 89 amino acids of γ-zein, including the repeated and the Pro-rich domains, maintains the main characteristics of wild-type γ-zein: It is insoluble unless its disulfide bonds are reduced and forms ER-located protein bodies. Unlike wild-type phaseolin, the protein, which we called zeolin, accumulates to very high amounts in leaves of transgenic tobacco (Nicotiana tabacum). A relevant proportion of the ER chaperone BiP is associated with zeolin protein bodies in an ATP-sensitive fashion. Pulse-chase labeling confirms the high affinity of BiP to insoluble zeolin but indicates that, unlike structurally defective proteins that also extensively interact with BiP, zeolin is highly stable. We conclude that the γ-zein portion is sufficient to induce the formation of protein bodies also when fused to another protein. Because the storage proteins of cereals and legumes nutritionally complement each other, zeolin can be used as a starting point to produce nutritionally balanced and highly stable chimeric storage proteins.

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The Endoplasmic Reticulum: Gateway of the Secretory Pathway

Cited by 110 publications

References 40 publications

The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum

The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum

Localization of Organelle Proteins by Isotope Tagging (LOPIT)

Zeolin. A New Recombinant Storage Protein Constructed Using Maize γ-Zein and Bean Phaseolin

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