Csg1p and Newly Identified Csh1p Function in Mannosylinositol Phosphorylceramide Synthesis by Interacting with Csg2p

Abstract

Csg1p and Csg2p have been shown to be involved in the synthesis of mannosylinositol phosphorylceramide (MIPC) from inositol phosphorylceramide. YBR161w, termed CSH1 here, encodes a protein that exhibits a strong similarity to Csg1p. To examine whether Csh1p also functions in MIPC synthesis, we performed a [ 3 H]dihydrosphingosine labeling experiment. ⌬csg1 cells exhibited only a reduction in the synthesis of mannosylated sphingolipids compared with wild-type cells, whereas the ⌬csg1 ⌬csh1 double deletion mutant exhibited a total loss. These results indicated that Csg1p and Csh1p have redundant functions in MIPC synthesis. Analyses using ⌬csg1 and ⌬csh1 cells in the ⌬ipt1, ⌬sur2, or ⌬scs7 genetic background demonstrated that Csh1p has a different substrate specificity from Csg1p. We also revealed that Csg2p interacts with both Csg1p and Csh1p. Deletion of the CSG2 gene reduced the Csg1p activity and abolished the Csh1p activity. These results suggested that two distinct inositol phosphorylceramide mannosyltransferase complexes, Csg1p-Csg2p and Csh1p-Csg2p, exist.

Alteration of complex sphingolipid composition and its physiological significance in yeast Saccharomyces cerevisiae lacking vacuolar ATPase

“…The increase in the MIPC levels was clearly observed after 5 h but not 1 h after the replacement. The Rf values of IPC-D and MIPC-A on the TLC plate overlapped under these experimental conditions (Uemura et al, 2003). Thus, we examined the complex sphingolipid composition with deletion of CCC2, which is required for the synthesis of D-type complex sphingolipids .…”

“…1). MIPC is formed through the addition of mannose to IPC, which is catalysed by two homologous IPC mannosyltransferases, Sur1 and Csh1, and Csg2 functions as a regulatory subunit for both Sur1 and Csh1 Uemura et al, 2003;Zhao et al, 1994) ( Fig. 1).…”

“…In addition, fluorescence recovery after photobleaching (FRAP) analysis revealed that loss of SCS7 and/or SUR2 affects the lateral diffusion of membrane proteins (Uemura et al, 2014). Loss of MIPC synthesis causes supersensitivity to Ca 2+ (Uemura et al, 2003;Zhao et al, 1994), rapid cell death under nitrogen starvation (Yamagata et al, 2013), and impairment of a specific endosomal trafficking pathway and cell integrity (Tani & Kuge, 2010, 2012Morimoto & Tani, 2015). In addition, MIPC regulates the activity of aminophospholipid flippases via Fpk1 and Fpk2 kinases, and phospholipid asymmetry in plasma membranes (Roelants et al, 2010).…”

Regulation of the Transport and Protein Levels of the Inositol Phosphorylceramide Mannosyltransferases Csg1 and Csh1 by the Ca2+-binding Protein Csg2

“…MIPC synthesis is catalyzed by either of two homologous IPC mannosyltransferases, Csg1 and Csh1, which prefer different IPC species as substrates (12,13). Cells carrying a double mutation, ⌬csg1 ⌬csh1, are sensitive to external Ca 2ϩ (5,12,14), suggesting a role for the GSLs in cellular stress response.…”

HOR7, a Multicopy Suppressor of the Ca2+-induced Growth Defect in Sphingolipid Mannosyltransferase-deficient Yeast

“…MIPC production requires the IPC mannosyltransferases Csg1p and Csh1p (8 -10) as well as an EF-Ca 2ϩ -binding domain-containing membrane protein, Csg2p (11). Csg2p interacts with Csg1p and Csh1p (9), but its precise role in MIPC production is unclear. Although Csg1p and Csh1p contain a region of homology with the yeast ␣-1,6-mannosyltransferase Och1p, Csg2p does not share this sequence and is not absolutely required for MIPC synthesis, suggesting that Csg2p serves a regulatory rather than a catalytic function.…”