High impact information on SUR1

• CCC1 was previously identified by complementation of a Ca2+-sensitive (csg1) mutant [1].
• Thus, Csg2 has several regulatory functions for Csg1 and Csh1, including stability, transport, and gene expression [2].
• One of the yeast complex sphingolipids, mannosylinositol phosphorylceramide (MIPC), is produced by the redundant inositol phosphorylceramide (IPC) mannosyltransferases Csg1 and Csh1 [2].
• Regulation of the Transport and Protein Levels of the Inositol Phosphorylceramide Mannosyltransferases Csg1 and Csh1 by the Ca2+-binding Protein Csg2 [2].
• We also demonstrated that Ca(2+) stimulates IPC-to-MIPC conversion, because of a Csg2-dependent increase in Csg1 levels [2].

Biological context of SUR1

• Here we show that open reading frame YBR161w, renamed CSH1, is functionally homologous to CSG1 and that deletion of both genes abolishes MIPC and M(IP)2C synthesis without affecting protein mannosylation [3].
• Loss of Csg1p and Csh1p has no effect on clathrin- or AP-3 adaptor-mediated protein transport from the Golgi to the vacuole [3].
• Suppression of cls2 was observed even after introduction of a single-copy plasmid harboring BCL21 [4].
• Analyses using Deltacsg1 and Deltacsh1 cells in the Deltaipt1, Deltasur2, or Deltascs7 genetic background demonstrated that Csh1p has a different substrate specificity from Csg1p [5].
• This gene displays non-allelic complementation of the Ca(2+)-sensitive phenotype conferred by the csg1 mutation [6].

Anatomical context of SUR1

• Increased osmolarity of the growth medium increases the Ca2+ tolerance of csg1 and csg2 mutant cells, suggesting that altered cell wall synthesis causes Ca(2+)-induced death [7].
• Further identification of the glycosylated residues suggests that both Csg1 and Csh1 exhibit membrane topology with their C termini in the cytosol and their mannosyltransferase domains in the lumen [2].

Associations of SUR1 with chemical compounds

• To confirm this hypothesis, a C. albicans gene homologue for the Saccharomyces cerevisiae SUR1 gene was identified and named MIT1 as it coded for GDP-mannose:inositol-phospho-ceramide mannose transferase [8].
• To better understand the molecular basis of the Ca(2+)-induced growth defect in IPC-C-overaccumulating cells, we searched for genes whose overexpression restored Ca(2+) tolerance in a mutant lacking the IPC mannosyltransferases Csg1p and Csh1p [9].
• Csg1p and Csg2p have been shown to be involved in the synthesis of mannosylinositol phosphorylceramide (MIPC) from inositol phosphorylceramide [5].

Physical interactions of SUR1

• We also revealed that Csg2p interacts with both Csg1p and Csh1p [5].

Regulatory relationships of SUR1

• Increased expression of CCC2 or increased Cu2+ concentration in the growth medium enhances the Ca2+ tolerance of csg1 mutants, suggesting that accumulation of IPC-C renders csg1 cells Ca2+ sensitive [7].
• BCL21 suppresses the cls2 disruption mutation, indicating that the multicopy suppression does not require the Cls2p [4].

Other interactions of SUR1

• Here we demonstrate that SUR1/CSG1 is both genetically and biochemically related to CSG2 [7].
• Ten mutants were obtained, ranged amongst four complementation groups, named SUR1, SUR2, SUR3 and SUR4 [10].
• A 93-amino acid stretch of Csg1p shows 29% identity with the alpha-1, 6-mannosyltransferase encoded by OCH1 [7].

References