Redox regulation of glutenin subunit assembly in the plant endoplasmic reticulum

Abstract

SUMMARYThe glutenin fraction of wheat storage proteins consists of large polymers in which high-and low-molecularweight subunits are connected by inter-chain disulfide bonds. We found that assembly of a low-molecularweight glutenin subunit in the endoplasmic reticulum is a rapid process that leads to accumulation of various oligomeric forms, and that this assembly is sensitive to perturbation of the cellular redox environment. In endoplasmic reticulum-derived microsomes, low-molecular-weight glutenin subunits are subjected to hyperpolymerization, indicating that cytosolic factors play an important role in limiting polymer size. Addition of physiological concentrations of reduced glutathione is sufficient to maintain the original polymerization pattern of the glutenin subunits upon cytosol dilution. Furthermore, we show that a low-molecular-weight glutenin subunit can be glutathionylated in endoplasmic reticulum-derived microsomes, and that it can be directly reduced by glutathione in vitro. These results indicate that glutenin polymerization is sensitive to changes in the redox state of the cell, and suggest that the presence of a reducing cytosolic environment plays an important role in regulating disulfide bond formation in the endoplasmic reticulum of plant cells.

Comparison of Thermobifida fusca Cellulases Expressed in Escherichia coli and Nicotiana tabacum Indicates Advantages of the Plant System for the Expression of Bacterial Cellulases

“…Therefore, the impairment of disulfide bond formation in the E. coli cytosol is a reasonable explanation for the observed lack of exocellulase expression in this system (de Marco, 2009). The plant ER environment promotes disulfide bond formation (Onda et al, 2009; Lombardi et al, 2012) supporting the hypothesis that exocellulase accumulation in E. coli is prevented by the inability to form disulfide bonds efficiently. This might lead to the degradation of unfolded proteins.…”

Intracellular glutathione pools are heterogeneously concentrated

“…Nonetheless, we propose that a relatively high [GS tot ] ER constitutes a general characteristic of ER physiology. Since the trapping of cytosolic GSH into the ER, which is known to bring about reductive input [21,26,27] , is directly driven by the organelle's oxidation level (see Fig. 5 ), we further suggest that [GS tot ] ER is an adjustable and “homeostatic” parameter.…”

Glutenin and Gliadin, a Piece in the Puzzle of their Structural Properties in the Cell Described through Monte Carlo Simulations

“…In the cell, both gliadins and glutenins are synthesized in the ribosomes of the rough endoplasmic reticulum (ER) and transported to ER lumen [9]. After this, the proteins form disulfide bonds between CYS, and the glutenins polymerize into polymers [10]. The formation of disulfide bonds is regulated by the cytosolic and redox conditions in the cell [10].…”