Proteolytic Processing Patterns of Prosaposin in Insect and Mammalian Cells

Leonova, Tatyana; Qi, Xiaoyang; Bencosme, A; Ponce, Elvira; Sun, Ying; Grabowski, Gregory A.

doi:10.1074/jbc.271.29.17312

Cited by 86 publications

(69 citation statements)

References 38 publications

(30 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1C). PS is proteolytically processed into mature saposins in a stepwise fashion (28), and we found that the PS deletion mutants were processed as efficiently as the wild type, shown in Fig. 1D Immunofluorescence analysis of saposin expression in PSKO2.CD1d cells expressing wild-type PS or PS mutants lacking individual saposins.…”

Section: Resultsmentioning

confidence: 77%

Saposin B is the dominant saposin that facilitates lipid binding to human CD1d molecules

Yuan

Tsang

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

102

View full text Add to dashboard Cite

CD1d molecules bind lipid antigens in the endocytic pathway, and access to the pathway is important for the development of CD1d-restricted natural killer T (NKT) cells. Saposins, derived from a common precursor, prosaposin, are small, heat-stable lysosomal glycoproteins required for lysosomal degradation of sphingolipids. Expression of prosaposin is required for efficient lipid binding and recognition of human CD1d molecules by NKT cells. Despite high sequence homology among the four saposins, they have different specificities for lipid substrates and different mechanisms of action. To determine the saposins involved in promoting lipid binding to CD1d, we expressed prosaposin deletion mutants lacking individual saposins in prosaposin-negative, CD1d-positive cells. No individual saposin proved to be absolutely essential, but the absence of saposin B resulted in the lowest recognition of α-galactosylceramide by NKT cells. When recombinant exogenous saposins were added to the prosaposin-negative cells, saposin B was the most efficient in restoring CD1d recognition. Saposin B was also the most efficient in mediating α-galactosylceramide binding to recombinant plate-bound CD1d and facilitating NKT cell activation. Saposin B could also mediate lipid binding to soluble CD1d molecules in a T cell-independent assay. The optimal pH for saposin B-mediated lipid binding to CD1d, pH 6, is higher than that of lysosomes, suggesting that saposin B may facilitate lipid binding to CD1d molecules throughout the endocytic pathway.

show abstract

Section: Resultsmentioning

confidence: 77%

Saposin B is the dominant saposin that facilitates lipid binding to human CD1d molecules

Yuan

Tsang

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

102

View full text Add to dashboard Cite

show abstract

“…Intriguingly, it has been reported that a group of lipid transfer proteins, saposins, require proteolytic processing by CatD to obtain their functional properties (33,34). Four saposins (A, B, C, D) are generated by proteolysis from the common precursor protein prosaposin.…”

Section: Resultsmentioning

confidence: 99%

Peroxisome Proliferator-Activated Receptor γ-Regulated Cathepsin D Is Required for Lipid Antigen Presentation by Dendritic Cells

Nakken

Varga

Szatmári

et al. 2011

The Journal of Immunology

View full text Add to dashboard Cite

It is well established that dendritic cells (DCs) take up, process, and present lipid Ags in complex with CD1d molecules to invariant NKT cells. The lipid-activated transcription factor, peroxisome proliferator-activated receptor γ (PPARγ), has previously been shown to regulate CD1d expression in human monocyte-derived DCs, providing a link between lipid metabolism and lipid Ag presentation. We report that PPARγ regulates the expression of a lysosomal protease, cathepsin D (CatD), in human monocyte-derived DCs. Inhibition of CatD specifically reduced the expansion of invariant NKT cells and furthermore resulted in decreased maturation of saposins, a group of lipid transfer proteins required for lysosomal lipid Ag processing and loading. These results reveal a novel mechanism of lipid Ag presentation and identify CatD as a key component of this machinery and firmly place PPARγ as the transcriptional regulator linking lipid metabolism and lipid Ag processing.

show abstract

“…The organization of several SAPLIP elements within one precursor molecule is not a unique feature of naegleriapores, as saposins A-D and the surfactant-associated protein B also are proteolytically processed from a multipeptide molecule (12)(13)(14)(15). The processing of multiple antibacterial peptides from one large precursor molecule may constitute an efficient mode for the simultaneous synthesis of different effector molecules, thereby resulting in amplification of the antibacterial response and an expansion of the target cell spectrum.…”

Section: Discussionmentioning

confidence: 99%

Antimicrobial and Pore-forming Peptides of Free-living and Potentially Highly Pathogenic Naegleria fowleri Are Released from the Same Precursor Molecule

Herbst

Marciano‐Cabral

Leippe

2004

Journal of Biological Chemistry

View full text Add to dashboard Cite

The pore-forming polypeptides of Naegleria fowleri, naegleriapores A and B, are processed from separate multipeptide precursor structures. According to their transcripts, each precursor molecule appears to contain additional naegleriapore-like polypeptides, all of which share a structural motif of six invariant cysteine residues within their amino acid sequence. To identify the putative pronaegleriapore-derived peptides at the protein level, amoebic extracts were screened for small cysteine-rich polypeptides by fluorescently labeling their cysteine residues. Three novel naegleriapore isoforms derived from the precursor molecule of naegleriapore B were identified. Two of the isoforms were purified to homogeneity and tested for their biological activity. The pore-forming activity of the novel peptides was remarkably lower than that of the originally isolated naegleriapores, but both peptides killed bacteria by permeabilizing their cytoplasmic membranes. Collectively, these results indicate that naegleriapore isoforms with antibacterial and pore-forming activity are proteolytically released from the same precursor protein, presumably to generate a phylogenetically ancient complementary antimicrobial arsenal.Naegleria fowleri is a free-living amoeboflagellate of soil and freshwater habitats throughout the world. Although the trophozoites are able to fulfil their life cycle without the intervention of a parasitic stage, they can invade the human brain via the nasal mucosa and olfactory nerve and cause primary amoebic meningoencephalitis (1, 2). This disease is characterized by massive host tissue destruction indicating that the cytolytic activity of the amoebae is a major factor for their pathogenicity.In vitro, intact amoebae (1), as well as cell-free extracts thereof (3), lyse efficiently a variety of target cells. The amoebic cytolytic capacity has been attributed mainly to pore-forming molecules that have been identified more than a decade ago (4). Recently, we characterized at the molecular level naegleriapores A and B, proteins that potently display pore-forming activity that kills prokaryotic as well as eukaryotic target cells (5). According to the respective transcripts, both naegleriapores were processed from larger precursor structures, each of which contains several naegleriapore isoforms that share the structural motif of six invariant cysteine residues within their highly diverse amino acid sequences. The precursor molecule of naegleriapore A contains three isoforms, and that of naegleriapore B contains five isoforms (5). For convenience, the putative isoforms within the precursor molecules were designated according to their location on the precursor of naegleriapore A as A1-A3 and on that of naegleriapore B as B1-B5. Isoforms A2 and B1 represent proteins that have been isolated recently by us according to their pore-forming activity (5).As the existence, fate, and function of additional naegleriapores contained in the precursor molecules are unclear, we initiated a survey pursuant to their identificatio...

show abstract

Proteolytic Processing Patterns of Prosaposin in Insect and Mammalian Cells

Cited by 86 publications

References 38 publications

Saposin B is the dominant saposin that facilitates lipid binding to human CD1d molecules

Saposin B is the dominant saposin that facilitates lipid binding to human CD1d molecules

Peroxisome Proliferator-Activated Receptor γ-Regulated Cathepsin D Is Required for Lipid Antigen Presentation by Dendritic Cells

Antimicrobial and Pore-forming Peptides of Free-living and Potentially Highly Pathogenic Naegleria fowleri Are Released from the Same Precursor Molecule

Contact Info

Product

Resources

About