Structure, assembly, and secretion of octameric invertase.

Area of Science:

• Biochemistry
• Cell Biology
• Protein Folding

Background:

• Yeast invertase is a secreted enzyme essential for sucrose metabolism.
• Protein folding and assembly occur in the endoplasmic reticulum lumen.
• Proper protein oligomerization is crucial for function and localization.

Purpose of the Study:

• To investigate the assembly and quaternary structure of yeast invertase.
• To determine the role of glycosylation in invertase oligomerization.
• To understand how invertase oligomerization affects its retention in the periplasmic space.

Main Methods:

• Purification of yeast invertase from wild-type and mutant yeast cells (sec18).
• Analysis of invertase structure using negative staining electron microscopy.
• In vitro dissociation and reassociation studies of purified invertase.
• Selective release of invertase from intact yeast cells.

Main Results:

• Yeast invertase forms a stable homo-octamer during assembly in the endoplasmic reticulum.
• Invertase remains an octamer throughout the secretion pathway, with increasing glycosylation.
• N-linked carbohydrate facilitates octamer assembly both in vitro and in vivo.
• Dissociated dimers can reassociate into octamers in the presence of polyethylene glycol.
• Oligomerization appears to retain invertase in the periplasmic space.

Conclusions:

• Yeast invertase assembly results in a stable homo-octameric structure.
• N-linked glycosylation is a key factor in yeast invertase oligomerization.
• The homo-octameric structure of invertase plays a role in its localization and retention within the yeast cell.