More than 30 years ago it was observed that the storage proteins of maize (Zea mays) seeds accumulate as "bulges or localized dilatations along the endoplasmic reticulum cisternae" of developing endosperm cells (Khoo and Wolf, 1970). It later became evident that, whereas the widespread seed storage proteins of the 7S and 11S classes travel from the endoplasmic reticulum (ER) to the Golgi complex and are then deposited in vacuoles, a number of cereal storage proteins instead form electron-dense, round-shaped structures with diameters of 0.5 to 2.0 µm, termed protein bodies, within the ER lumen (Herman and Larkins, 1999). These large aggregates are then either permanently stored in the ER or delivered to storage vacuoles by unconventional protein traffic pathways. Today, the mechanisms by which some of the most important proteins for human nutrition form protein bodies within the ER remain a fascinating but still puzzling issue in cell biology. This developmentally programmed use of the ER to store vast amounts of specific proteins in highly condensed forms has been found only in plants. On the other hand, aggregation of newly synthesized proteins in the ER, due to stress or genetic defects, is usually treated by the cell as a pathology that must be avoided by disposing of the misfolded proteins (Sitia and Braakman, 2003). Many ER resident proteins indeed have the role of preventing protein aggregation, maintaining nascent and newly synthesized polypeptides in a state that is compatible with further structural maturation or, for defective proteins, with degradation. Thus, proteins destined for storage in the ER must have evolved to condense in a controlled fashion and thus to avoid both export from the ER and degradation. How this might be achieved is the topic of this update.
Protein quality control mechanisms and protein storage in the endoplasmic reticulum. A conflict of interests?
Vitale A;Ceriotti A
2004-01-01
Abstract
More than 30 years ago it was observed that the storage proteins of maize (Zea mays) seeds accumulate as "bulges or localized dilatations along the endoplasmic reticulum cisternae" of developing endosperm cells (Khoo and Wolf, 1970). It later became evident that, whereas the widespread seed storage proteins of the 7S and 11S classes travel from the endoplasmic reticulum (ER) to the Golgi complex and are then deposited in vacuoles, a number of cereal storage proteins instead form electron-dense, round-shaped structures with diameters of 0.5 to 2.0 µm, termed protein bodies, within the ER lumen (Herman and Larkins, 1999). These large aggregates are then either permanently stored in the ER or delivered to storage vacuoles by unconventional protein traffic pathways. Today, the mechanisms by which some of the most important proteins for human nutrition form protein bodies within the ER remain a fascinating but still puzzling issue in cell biology. This developmentally programmed use of the ER to store vast amounts of specific proteins in highly condensed forms has been found only in plants. On the other hand, aggregation of newly synthesized proteins in the ER, due to stress or genetic defects, is usually treated by the cell as a pathology that must be avoided by disposing of the misfolded proteins (Sitia and Braakman, 2003). Many ER resident proteins indeed have the role of preventing protein aggregation, maintaining nascent and newly synthesized polypeptides in a state that is compatible with further structural maturation or, for defective proteins, with degradation. Thus, proteins destined for storage in the ER must have evolved to condense in a controlled fashion and thus to avoid both export from the ER and degradation. How this might be achieved is the topic of this update.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
