Disease relevance of OCH1

• A series of influenza virus hemagglutinin (HA) epitope-tagged fusion proteins was constructed in which invertase is appended to the Golgi-luminal carboxy terminus of full-length Och1p [1].

High impact information on OCH1

• At steady state, de novo-synthesized and TGN-generated HA epitope-tagged Och1p reside in a compartment with a buoyant density identical to that of wild-type Och1p and distinct from that of the vacuole or the TGN [1].
• The Och1p-Kex2p site-invertase fusion protein is cleaved with a half-time of 5 min, and the process proceeds to completion [1].
• To analyze the mechanism of integral membrane protein localization in the early Golgi apparatus of Saccharomyces cerevisiae, we have used Och1p, a cis-Golgi mannosyltransferase [1].
• Finally, och1 null cells that express an Ochlp fusion construct known to rapidly encounter the TGN glycosylate invertase to the same extent as wild-type cells, indicating that they have phenotypically wild-type Och1p activity [1].
• Subcellular fractionation revealed that > 90% of the alpha 1,6 mannose-modified fusion protein colocalized with the ER (Wbp1p) and not with the Golgi Och1p-containing compartment or other membrane fractions [2].

Biological context of OCH1

• We have cloned the OCH1 gene by complementation of temperature sensitive (ts) phenotype for growth [3].
• The OCH1 gene disruptant is not lethal but ts for cell growth, and lacks mannose outer chains [3].
• Most interestingly, Hpocr1Delta showed a severe defect in the O-linked glycosylation of extracellular chitinase, representing HpOCR1 as a novel member of the OCH1 family implicated in both N- and O-linked glycosylation [4].
• Our studies reveal that the Skn7p HSF-like DNA binding domain interacts with a cis-acting element identified upstream of OCH1 that is distinct from the previously defined HSE-like Skn7p binding site [5].
• Cloning, sequencing and disruption of NGD29 showed that it is a non lethal gene and identical to OCH1 [6].

Anatomical context of OCH1

• Our results suggest that the blocking of vesicle transport by a loss of the Trs130p function causes some defect in the cell wall mannoproteins, which leads to the elevated expression of OCH1 through the Skn7p function, to compensate for the defect [7].
• The Saccharomyces cerevisiae Och1p is required for the initiation of the mannose outer chain elongation of cell wall mannoproteins [7].
• In vitro translation/translocation analysis revealed that the large C-terminal region of the OCH1 protein is located at the lumenal side of microsomal membranes with some sugar modification, indicating a type II membrane topology [3].
• The OCH1 protein was detected in yeast membrane fractions as four forms of 58-66 kDa, which correspond to the size of a glycoprotein containing four N-linked sugar chains the length of which is almost the same or slightly larger than the inner core (Man8GlcNAc2) formed in the endoplasmic reticulum (ER) [3].
• We find that Och1p does not cycle via endosomes during its normal itinerary suggesting that Och1p engages in intra-Golgi cycling only [8].

Associations of OCH1 with chemical compounds

• The Saccharomyces cerevisiae OCH1 gene encodes an alpha-1,6-mannosyltransferase that initiates the polymannose outer chain elongation of N-linked glycans [9].
• OCH1 encodes a novel membrane bound mannosyltransferase: outer chain elongation of asparagine-linked oligosaccharides [3].
• The eukaryotic two-component histidine kinase Sln1p regulates OCH1 via the transcription factor, Skn7p [5].
• Man8GlcNAcOH that involves an open sugar ring by reduction of reducing terminal GlcNAc residue did not serve as an acceptor for Och1p [10].
• These results contrast the far simpler glycan profile found in Saccharomyces cerevisiae alg3-1 och1, indicating diverging Golgi processing in these two closely related yeasts [11].

Other interactions of OCH1

• A 93-amino acid stretch of Csg1p shows 29% identity with the alpha-1, 6-mannosyltransferase encoded by OCH1 [12].
• In this study, we attempted to gain an understanding of the relationship between the defect in the Trs130p function and the elevated expression of OCH1 [7].
• We suggest that transcriptional control of OCH1 by cdc4(bon) is through Swi4, because cdc4(bon) cannot activate the OCH1-lacZ reporter in a strain deleted for SWI4 [9].
• The HOC1 gene (Homologous to OCH1) is predicted to encode a type II integral membrane protein that strongly resembles Och 1p, an alpha-1,6-mannosyltransferase [13].
• Subcellular fractionation experiments indicated that the fractionation pattern of Rer1p was similar to that of an early Golgi protein, Och1p [14].

Analytical, diagnostic and therapeutic context of OCH1

• Mannosyltransferase activity of OCH1 gene product (Och1p) was measured on HPLC by using pyridylaminated Man8GlcNAc2 (Man8GlcNAc2-PA) as an acceptor and the reaction product was observed at the retention time corresponding to Man9GlcNAc2-PA [10].

References