Dataset Information

Glycosylphosphatidylinositol-anchor intermediates associate with triton-insoluble membranes in subcellular compartments that include the endoplasmic reticulum.

ABSTRACT: Glycosylphosphatidylinositol (GPI)-anchored proteins are resistant to solubilization with Triton X-100 at 4 degrees C, and they can be recovered in Triton-insoluble membranes (TIMs) that float to a characteristic buoyant density. Because the GPI structure itself has been shown to target GPI-anchored proteins to TIMs, we investigated the association of GPI-anchor intermediates with TIMs. GPI-anchor biosynthesis involves a pathway of some 10 steps that take place in the endoplasmic reticulum (ER). These intermediates include glucosaminyl-acylphosphatidylinositol [GlcN-(acyl)PI] and later mannosylated GPIs, denoted H6, H7 and H8, that are present not only in the ER but also in other cell compartments, including the plasma membrane. At least two-thirds of the GlcN-(acyl)PI in HeLa D cells and mannosylated GPIs in K562 cells were found in TIMs. Although previous reports have considered TIMs to be derived primarily from the plasma membrane, we recovered TIMs from subcellular fractions enriched in ER membranes. The ER marker calnexin and GPI-anchored proteins as well as N-acetylglucosaminyl-phosphatidylinositol and mannosylated GPIs were present in ER-TIMs. Interestingly, GlcN-PI and H7 were less enriched in ER-TIM than the other GPIs, suggesting that ER-TIMs might reflect a compartmentalization of the GPI-anchor biosynthetic pathway in the ER.

SUBMITTER: Sevlever D

PROVIDER: S-EPMC1220595 | biostudies-other | 1999 Nov

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Glycosylphosphatidylinositol (GPI)-anchored proteins are cell surface-localized proteins that serve many important cellular functions. The pathway mediating synthesis and attachment of the GPI anchor to these proteins in eukaryotic cells is complex, highly conserved, and plays a critical role in the proper targeting, transport, and function of all GPI-anchored protein family members. In this article, we demonstrate that MCD4, an essential gene that was initially identified in a genetic screen to isolate Saccharomyces cerevisiae mutants defective for bud emergence, encodes a previously unidentified component of the GPI anchor synthesis pathway. Mcd4p is a multimembrane-spanning protein that localizes to the endoplasmic reticulum (ER) and contains a large NH2-terminal ER lumenal domain. We have also cloned the human MCD4 gene and found that Mcd4p is both highly conserved throughout eukaryotes and has two yeast homologues. Mcd4p's lumenal domain contains three conserved motifs found in mammalian phosphodiesterases and nucleotide pyrophosphases; notably, the temperature-conditional MCD4 allele used for our studies (mcd4-174) harbors a single amino acid change in motif 2. The mcd4-174 mutant (1) is defective in ER-to-Golgi transport of GPI-anchored proteins (i.e., Gas1p) while other proteins (i.e., CPY) are unaffected; (2) secretes and releases (potentially up-regulated cell wall) proteins into the medium, suggesting a defect in cell wall integrity; and (3) exhibits marked morphological defects, most notably the accumulation of distorted, ER- and vesicle-like membranes. mcd4-174 cells synthesize all classes of inositolphosphoceramides, indicating that the GPI protein transport block is not due to deficient ceramide synthesis. However, mcd4-174 cells have a severe defect in incorporation of [3H]inositol into proteins and accumulate several previously uncharacterized [3H]inositol-labeled lipids whose properties are consistent with their being GPI precursors. Together, these studies demonstrate that MCD4 encodes a new, conserved component of the GPI anchor synthesis pathway and highlight the intimate connections between GPI anchoring, bud emergence, cell wall function, and feedback mechanisms likely to be involved in regulating each of these essential processes. A putative role for Mcd4p as participating in the modification of GPI anchors with side chain phosphoethanolamine is also discussed.

Project description:Erythrocyte shape and membrane integrity is imparted by the membrane skeleton, which can be isolated as a Triton X-100 insoluble structure that retains the biconcave shape of intact erythrocytes, indicating isolation of essentially intact membrane skeletons. These erythrocyte "Triton Skeletons" have been studied morphologically and biochemically, but unbiased proteome analysis of this substructure of the membrane has not been reported. In this study, different extraction buffers and in-depth proteome analyses were used to more fully define the protein composition of this functionally critical macromolecular complex. As expected, the major, well-characterized membrane skeleton proteins and their associated membrane anchors were recovered in good yield. But surprisingly, a substantial number of additional proteins that are not considered in erythrocyte membrane skeleton models were recovered in high yields, including myosin-9, lipid raft proteins (stomatin, flotillin1 and 2), multiple chaperone proteins (HSPs, protein disulfide isomerase and calnexin), and several other proteins. These results show that the membrane skeleton is substantially more complex than previous biochemical studies indicated, and it apparently has localized regions with unique protein compositions and functions. This comprehensive catalog of the membrane skeleton should lead to new insights into erythrocyte membrane biology and pathogenic mutations that perturb membrane stability. Biological significance Current models of erythrocyte membranes describe fairly simple homogenous structures that are incomplete. Proteome analysis of the erythrocyte membrane skeleton shows that it is quite complex and includes a substantial number of proteins whose roles and locations in the membrane are not well defined. Further elucidation of interactions involving these proteins and definition of microdomains in the membrane that contain these proteins should yield novel insights into how the membrane skeleton produces the normal biconcave erythrocyte shape and how it is perturbed in pathological conditions that destabilize the membrane.

Dataset Information

Glycosylphosphatidylinositol-anchor intermediates associate with triton-insoluble membranes in subcellular compartments that include the endoplasmic reticulum.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets