Htm1 protein generates the N-glycan signal for glycoprotein degradation in the endoplasmic reticulum.

To maintain protein homeostasis in secretory compartments, eukaryotic cells harbor a quality control system that monitors protein folding and protein complex assembly in the endoplasmic reticulum (ER). Proteins that do not fold properly or integrate into cognate complexes are degraded by ER-associated degradation (ERAD) involving retrotranslocation to the cytoplasm and proteasomal peptide hydrolysis. N-linked glycans are essential in glycoprotein ERAD; the covalent oligosaccharide structure is used as a signal to display the folding status of the host protein.

Transport of Na(+) and K (+) by an antiporter-related subunit from the Escherichia coli NADH dehydrogenase I produced in Saccharomyces cerevisiae.

The NADH dehydrogenase I from Escherichia coli is a bacterial homolog of the mitochondrial complex I which translocates Na(+) rather than H(+). To elucidate the mechanism of Na(+) transport, the C-terminally truncated NuoL subunit (NuoL(N)) which is related to Na(+)/H(+) antiporters was expressed as a protein A fusion protein (ProtA-NuoL(N)) in the yeast Saccharomyces cerevisiae which lacks an endogenous complex I. The fusion protein inserted into membranes from the endoplasmatic reticulum (ER), as confirmed by differential centrifugation and Western analysis.

Systematic screening of polyphosphate (poly P) levels in yeast mutant cells reveals strong interdependence with primary metabolism.

Background: Inorganic polyphosphate (poly P) occurs universally in all organisms from bacteria to man. It functions, for example, as a phosphate and energy store, and is involved in the activation and regulation of proteins. Despite its ubiquitous occurrence and important functions, it is unclear how poly P is synthesized or how poly P metabolism is regulated in higher eukaryotes.

Yos9 protein is essential for degradation of misfolded glycoproteins and may function as lectin in ERAD.

The Htm1/EDEM protein has been proposed to act as a "degradation lectin" for endoplasmic reticulum-associated degradation (ERAD) of misfolded glycoproteins. In this study, we provide genetic and biochemical evidence that Yos9 protein in Saccharomyces cerevisiae is essential for efficient degradation of mutant glycoproteins. Yos9 is a member of the OS-9 protein family, which is conserved among eukaryotes and shows similarities with mannose-6-phosphate receptors (MPRs).

Biosynthesis of lipid-linked oligosaccharides in Saccharomyces cerevisiae: Alg13p and Alg14p form a complex required for the formation of GlcNAc(2)-PP-dolichol.

N-Glycosylation in the endoplasmic reticulum is an essential protein modification and highly conserved in evolution from yeast to man. Here we identify and characterize two essential yeast proteins having homology to bacterial glycosyltransferases, designated Alg13p and Alg14p, as being required for the formation of GlcNAc(2)-PP-dolichol (Dol), the second step in the biosynthesis of the unique lipid-linked core oligosaccharide. Down-regulation of each gene led to a defect in protein N-glycosylation and an accumulation of GlcNAc(1)-PP-Dol in vivo as revealed by metabolic labeling with [(3)H]glucosamine.

Major histocompatibility complex class I molecules expressed with monoglucosylated N-linked glycans bind calreticulin independently of their assembly status.

The assembly of major histocompatibility complex (MHC) class I molecules with peptides in the endoplasmic reticulum (ER) is a critical step in the presentation of viral antigens to CD8+ T cells. This process is subject to quality control restrictions that prevent free class I heavy chains (HCs) and peptide-free HC-beta(2)-microglobulin (beta(2)m) dimers from exiting the ER. The lectin-like chaperone calreticulin associates with HC-beta(2)m heterodimers prior to peptide binding, but its precise role in regulating the subsequent events of peptide association and ER to Golgi transport remains undefined.

Two distinctly localized p-type ATPases collaborate to maintain organelle homeostasis required for glycoprotein processing and quality control.

Membrane transporter proteins are essential for the maintenance of cellular ion homeostasis. In the secretory pathway, the P-type ATPase family of transporters is found in every compartment and the plasma membrane. Here, we report the identification of COD1/SPF1 (control of HMG-CoA reductase degradation/SPF1) through genetic strategies intended to uncover genes involved in protein maturation and endoplasmic reticulum (ER)-associated degradation (ERAD), a quality control pathway that rids misfolded proteins.