scholarly journals The chaperone-binding activity of the mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

Cell Reports ◽  
2021 ◽  
Vol 35 (1) ◽  
pp. 108936
Author(s):  
Sandra Backes ◽  
Yury S. Bykov ◽  
Tamara Flohr ◽  
Markus Räschle ◽  
Jialin Zhou ◽  
...  
Keyword(s):  
Binding Activity ◽  
Induced Stress ◽  
Surface Receptor ◽  
Chaperone Binding

scholarly journals The mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

2020 ◽  
Author(s):  
Sandra Backes ◽  
Yury S. Bykov ◽  
Markus Räschle ◽  
Jialin Zhou ◽  
Svenja Lenhard ◽  
...  
Keyword(s):  
Mitochondrial Membrane ◽  
Surface Protein ◽  
Mitochondrial Proteins ◽  
Outer Mitochondrial Membrane ◽  
Induced Stress ◽  
Precursor Proteins ◽  
Surface Receptor ◽  
Chaperone Binding

SummaryMost mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers. Using in vivo methods and high content screens, we revisited the question of Tom70 function and considerably expanded the set of Tom70-dependent mitochondrial proteins. We demonstrate that the crucial activity of Tom70 is its ability to recruit cytosolic chaperones to the outer membrane. Indeed, tethering an unrelated chaperone-binding domain onto the mitochondrial surface complements most of the defects caused by Tom70 deletion. Tom70-mediated chaperone recruitment reduces the proteotoxicity of mitochondrial precursor proteins, in particular of hydrophobic inner membrane proteins. Thus, our work suggests that the predominant function of Tom70 is to tether cytosolic chaperones to the outer mitochondrial membrane, rather than to serve as a mitochondria-specifying targeting receptor.

Sialylation of the Sialic Acid Binding Lectin Sialoadhesin Regulates Its Ability to Mediate Cell Adhesion

Blood ◽  
1999 ◽  
Vol 93 (4) ◽  
pp. 1245-1252 ◽  
Author(s):  
Yvonne C. Barnes ◽  
Tim P. Skelton ◽  
Ivan Stamenkovic ◽  
Dennis C. Sgroi
Keyword(s):  
Sialic Acid ◽  
Inhibitory Effect ◽  
Binding Activity ◽  
Cell Surface Receptor ◽  
Common Mechanism ◽  
Specific Cell ◽  
Sialic Acid Binding ◽  
Surface Receptor ◽  
Mediate Cell

The macrophage-specific cell surface receptor sialoadhesin, which is a member of the newly recognized family of sialic acid binding lectins called siglecs, binds glycoprotein and glycolipid ligands containing a2-3–linked sialic acid on the surface of several leukocyte subsets. Recently, the sialic acid binding activity of the siglec CD22 has been demonstrated to be regulated by sialylation of the CD22 receptor molecule. In the present work, we show that desialylation of in vivo macrophage sialylconjugates enhances sialoadhesin-mediated lectin activity. Herein, we show that receptor sialylation of soluble sialoadhesin inhibits its binding to Jurkat cell ligands, and that charge-dependent repulsion alone cannot explain this inhibition. Furthermore, we show that the inhibitory effect of sialic acid is partially dependent on the presence of an intact exocyclic side chain. These results, in conjunction with previous findings, suggest that sialylation of siglecs by specific glycosyltransferases may be a common mechanism by which siglec-mediated adhesion is regulated.

scholarly journals Carbohydrate recognition in the peripheral nervous system: a calcium-dependent membrane binding site for HNK-1 reactive glycolipids potentially involved in Schwann cell adhesion.

1993 ◽  
Vol 121 (2) ◽  
pp. 397-408 ◽  
Author(s):  
L K Needham ◽  
R L Schnaar
Keyword(s):  
Nervous System ◽  
Cell Adhesion ◽  
Schwann Cell ◽  
Binding Site ◽  
Peripheral Nervous System ◽  
Specific Binding ◽  
Binding Activity ◽  
Cell Surface Receptor ◽  
Calcium Dependent ◽  
Surface Receptor

The carbohydrate determinants recognized by the HNK-1 antibody are potential cell-cell recognition ligands in the peripheral nervous system (PNS). The HNK-1 reactive sulfoglucuronylneolacto (SGNL) glycolipids specifically support Schwann cell adhesion, suggesting the presence of a cell surface receptor specific for SGNL-oligosaccharides. We directly probed PNS membranes for receptors complementary to SGNL determinants using a synthetic radioligand consisting of radioiodinated serum albumin derivatized with multiple SGNL-oligosaccharides. A high-affinity, saturable, calcium-dependent binding site for this ligand was found in PNS myelin membranes. Binding activity was carbohydrate-specific (most potently inhibited by SGNL-lipids compared to other glycolipids) and PNS-specific (absent from comparable central nervous system membranes). The SGNL-specific binding activity on PNS membranes reported here may be involved in peripheral myelination or myelin stabilization.

scholarly journals The hyaluronate receptor is associated with actin filaments.

1987 ◽  
Vol 105 (3) ◽  
pp. 1395-1404 ◽  
Author(s):  
B E Lacy ◽  
C B Underhill
Keyword(s):  
Actin Filaments ◽  
Binding Activity ◽  
Dnase I ◽  
Cell Surface Receptor ◽  
Insoluble Residue ◽  
3T3 Cells ◽  
Whole Cells ◽  
Surface Receptor ◽  
Swiss 3T3 ◽  
Triton X

The cell-surface receptor for hyaluronate is an integral membrane glycoprotein of Mr 85,000 (Underhill, C. B., A. L. Thurn, and B. E. Lacy, 1985, J. Biol. Chem., 260:8128-8133) that is thought to mediate many of the effects that hyaluronate has on cell behavior, such as migration, angiogenesis, and phagocytosis. To determine if the receptor is associated with the underlying cytoskeleton, Swiss 3T3 cells were extracted with a solution of Triton X-100, which solubilized most of the cellular components, but which left behind an insoluble residue containing the cytoskeleton. This detergent-insoluble residue was found to contain the bulk of the hyaluronate-binding activity, suggesting that the receptor might indeed be associated with the cytoskeleton. To further define the cytoskeletal element with which the receptor interacts, 3T3 cells were extracted with Triton X-100 under a variety of different ionic conditions. In each case, the amount of hyaluronate-binding activity in the detergent-insoluble residue was related to the amount of actin present, but not to either tubulin or vimentin. In addition, the recovery of hyaluronate-binding activity was dramatically enhanced (to 100% in most cases) if the cells were extracted in the presence of phalloidin, a drug that stabilizes actin filaments. However, the recovery of binding activity was dramatically decreased when whole cells were treated with cytochalasin B before extraction, and when extracted cells were treated with DNase I, which promotes the depolymerization of actin filaments. In addition, preincubating an extract of SV-40-transformed Swiss 3T3 cell membranes with DNase I caused a change in the elution profile of the receptor as judged by molecular-sieve chromatography. Presumably this decrease in the size of the receptor is due to the loss of associated actin filaments. The results of these experiments strongly suggest that the receptor for hyaluronate is associated either directly or indirectly with cytosolic actin filaments.

scholarly journals BRAFV600E mutation, TIMP-1 upregulation, and NF-κB activation: closing the loop on the papillary thyroid cancer trilogy

2011 ◽  
Vol 18 (6) ◽  
pp. 669-685 ◽  
Author(s):  
Alessandra Bommarito ◽  
Pierina Richiusa ◽  
Elvira Carissimi ◽  
Giuseppe Pizzolanti ◽  
Vito Rodolico ◽  
...  
Keyword(s):  
Thyroid Cancer ◽  
Mapk Pathway ◽  
Surface Membrane ◽  
Binding Activity ◽  
Common Mutation ◽  
Papillary Thyroid ◽  
Akt Phosphorylation ◽  
Surface Receptor ◽  
Closing The Loop ◽  
Apoptotic Activity

BRAFV600E is the most common mutation found in papillary thyroid carcinoma (PTC). Tissue inhibitor of metalloproteinases (TIMP-1) and nuclear factor (NF)-κB have been shown to play an important role in thyroid cancer. In particular, TIMP-1 binds its receptor CD63 on cell surface membrane and activates Akt signaling pathway, which is eventually responsible for its anti-apoptotic activity. The aim of our study was to evaluate whether interplay among these three factors exists and exerts a functional role in PTCs. To this purpose, 56 PTC specimens were analyzed for BRAFV600E mutation, TIMP-1 expression, and NF-κB activation. We found that BRAFV600E mutation occurs selectively in PTC nodules and is associated with hyperactivation of NF-κB and upregulation of both TIMP-1 and its receptor CD63. To assess the functional relationship among these factors, we first silenced BRAF gene in BCPAP cells, harboring BRAFV600E mutation. We found that silencing causes a marked decrease in TIMP-1 expression and NF-κB binding activity, as well as decreased invasiveness. After treatment with specific inhibitors of MAPK pathway, we found that only sorafenib was able to increase IκB-α and reduce both TIMP-1 expression and Akt phosphorylation in BCPAP cells, indicating that BRAFV600E activates NF-κB and this pathway is MEK-independent. Taken together, our findings demonstrate that BRAFV600E causes upregulation of TIMP-1 via NF-κB. TIMP-1 binds then its surface receptor CD63, leading eventually to Akt activation, which in turn confers antiapoptotic behavior and promotion of cell invasion. The recognition of this functional trilogy provides insight on how BRAFV600E determines cancer initiation, progression, and invasiveness in PTC, also identifying new therapeutic targets for the treatment of highly aggressive forms.

scholarly journals Identification of diphtheria toxin receptor and a nonproteinous diphtheria toxin-binding molecule in Vero cell membrane.

1988 ◽  
Vol 107 (2) ◽  
pp. 511-519 ◽  
Author(s):  
E Mekada ◽  
Y Okada ◽  
T Uchida
Keyword(s):  
Cell Membrane ◽  
Vero Cell ◽  
Diphtheria Toxin ◽  
Vero Cells ◽  
Binding Activity ◽  
Membrane Preparation ◽  
Toxin Binding ◽  
Surface Receptor ◽  
Toxin Receptor ◽  
Cell Membrane Preparation

Two substances possessing the ability to bind to diphtheria toxin (DT) were found to be present in a membrane fraction from DT-sensitive Vero cells. One of these substances was found on the basis of its ability to bind DT and inhibit its cytotoxic effect. This inhibitory substance competitively inhibited the binding of DT to Vero cells. However this inhibitor could not bind to CRM197, the product of a missense mutation in the DT gene, and did not inhibit the binding of CRM197 to Vero cells. Moreover, similar levels of the inhibitory activity were observed in membrane fractions from DT-insensitive mouse cells, suggesting the inhibitor is not the DT receptor which is specifically present in DT-sensitive cells. The second DT-binding substance was found in the same Vero cell membrane preparation by assaying the binding of 125I-labeled CRM197. Such DT-binding activity could not be observed in membrane preparation from mouse L cells. From competition studies using labeled DT and CRM proteins, we conclude that this binding activity is due to the surface receptor for DT. Treatment of these substances with several enzymes revealed that the inhibitor was sensitive to certain RNases but resistant to proteases, whereas the DT receptor was resistant to RNase but sensitive to proteases. The receptor was solubilized and partially purified by chromatography on CM-Sepharose column. Immunoprecipitation and Western blotting analysis of the partially purified receptor revealed that a 14.5-kD protein is the DT receptor, or at least a component of it.

scholarly journals Structure-function studies on human retinol-binding protein using site-directed mutagenesis

1994 ◽  
Vol 300 (2) ◽  
pp. 437-442 ◽  
Author(s):  
A Sivaprasadarao ◽  
J B Findlay
Keyword(s):  
Cell Surface ◽  
Specific Binding ◽  
Binding Protein ◽  
Specific Interaction ◽  
Binding Activity ◽  
Site Directed Mutagenesis ◽  
Retinol Binding Protein ◽  
Cell Surface Receptor ◽  
Directed Mutagenesis ◽  
Surface Receptor

Retinol-binding protein (RBP) transports vitamin A in the plasma. It consists of eight anti-parallel beta-strands (A to H) that fold to form an orthogonal barrel. The loops connecting the strands A and B, C and D, and E and F form the entrance to the binding site in the barrel. The retinol molecule is found deep inside this barrel. Apart from its specific interaction with retinol, RBP is involved in two other molecular-recognition properties, that is it binds to transthyretin (TTR), another serum protein, and to a cell-surface receptor. Using site-directed mutagenesis, specific changes were made to the loop regions of human RBP and the resultant mutant proteins were tested for their ability to bind to retinol, to TTR and to the RBP receptor. While all the variants retained their ability to bind retinol, that in which residues 92 to 98 of the loop E-F were deleted completely lost its ability to interact with TTR, but retained some binding activity for the receptor. In contrast, the double mutant in which leucine residues at positions 63 and 64 of the loop C-D were changed to arginine and serine respectively partially retained its TTR-binding ability, but completely lost its affinity for the RBP receptor. Mutation of Leu-35 of loop A-B to valine revealed no apparent effect on any of the binding activities of RBP. However, substitution of leucine for proline at position 35 markedly reduced the affinity of the protein for TTR, but showed no apparent change in its receptor-binding activity. These results demonstrate that RBP interacts with both TTR and the receptor via loops C-D and E-F. The binding sites, however, are overlapping rather than identical. RBP also appears to make an additional contact with TTR via its loop A-B. A further implication of these results is that RBP, when bound to TTR, cannot bind simultaneously to the receptor. This observation is consistent with our previously proposed mechanism for delivery of retinol to target tissues [Sivaprasadarao and Findlay (1988) Biochem. J. 255, 571-579], according to which retinol delivery involves specific binding of RBP to the cell-surface receptor, an interaction that triggers release of retinol from RBP to the bound cell rather than internalization of retinol-RBP complex.

scholarly journals Characterization and purification of proteins which bind high-density lipoprotein. A putative cell-surface receptor

1991 ◽  
Vol 279 (3) ◽  
pp. 633-641 ◽  
Author(s):  
H M Bond ◽  
G Morrone ◽  
S Venuta ◽  
K E Howell
Keyword(s):  
Cell Surface ◽  
High Density Lipoprotein ◽  
Gel Filtration ◽  
Density Lipoprotein ◽  
Binding Activity ◽  
Exchange Chromatography ◽  
High Density ◽  
Cell Surface Receptor ◽  
Binding Ability ◽  
Surface Receptor

High-density lipoprotein (HDL) is shown by ligand blotting to bind membrane-associated polypeptides with sizes of 60, 100 and 210 kDa. Binding was concentration-dependent and competed by excess unlabelled HDL. All the major apolipoproteins of HDL, apoA-I, apoA-II and apoA-IV, bound independently. The 100 kDa and 210 kDa HDL-binding activities were purified from membranes of Hep3B tumour cells by ion-exchange chromatography and gel filtration. The binding activities at 100 kDa and 210 kDa co-purified. After treatment with disulphide-reducing reagent, the 210 kDa band was no longer present and an increase was observed in the amount and binding ability of the 100 kDa polypeptide. The 100 kDa binding protein labelled at the cell surface with 125I could be immunoprecipitated after cross-linking to cell-surface-bound HDL. It is proposed that this HDL-binding activity, a putative cell-surface receptor for HDL, exists totally or in part as a high-molecular-mass complex composed of 100 kDa subunits.

Sialylation of the Sialic Acid Binding Lectin Sialoadhesin Regulates Its Ability to Mediate Cell Adhesion

Blood ◽  
1999 ◽  
Vol 93 (4) ◽  
pp. 1245-1252 ◽  
Author(s):  
Yvonne C. Barnes ◽  
Tim P. Skelton ◽  
Ivan Stamenkovic ◽  
Dennis C. Sgroi
Keyword(s):  
Sialic Acid ◽  
Inhibitory Effect ◽  
Binding Activity ◽  
Cell Surface Receptor ◽  
Common Mechanism ◽  
Specific Cell ◽  
Sialic Acid Binding ◽  
Surface Receptor ◽  
Mediate Cell

Abstract The macrophage-specific cell surface receptor sialoadhesin, which is a member of the newly recognized family of sialic acid binding lectins called siglecs, binds glycoprotein and glycolipid ligands containing a2-3–linked sialic acid on the surface of several leukocyte subsets. Recently, the sialic acid binding activity of the siglec CD22 has been demonstrated to be regulated by sialylation of the CD22 receptor molecule. In the present work, we show that desialylation of in vivo macrophage sialylconjugates enhances sialoadhesin-mediated lectin activity. Herein, we show that receptor sialylation of soluble sialoadhesin inhibits its binding to Jurkat cell ligands, and that charge-dependent repulsion alone cannot explain this inhibition. Furthermore, we show that the inhibitory effect of sialic acid is partially dependent on the presence of an intact exocyclic side chain. These results, in conjunction with previous findings, suggest that sialylation of siglecs by specific glycosyltransferases may be a common mechanism by which siglec-mediated adhesion is regulated.

scholarly journals Role of Aromatic Amino Acids in Receptor Binding Activity and Subunit Assembly of the Cytolethal Distending Toxin of Aggregatibacter actinomycetemcomitans

2008 ◽  
Vol 76 (7) ◽  
pp. 2812-2821 ◽  
Author(s):  
Linsen Cao ◽  
Georges Bandelac ◽  
Alla Volgina ◽  
Jonathan Korostoff ◽  
Joseph M. DiRienzo
Keyword(s):  
Amino Acids ◽  
Receptor Binding ◽  
Aromatic Amino Acids ◽  
Aggregatibacter Actinomycetemcomitans ◽  
Binding Activity ◽  
Cell Surface Receptor ◽  
Periodontal Pathogen ◽  
Cytolethal Distending Toxin ◽  
Receptor Binding Activity ◽  
Surface Receptor

ABSTRACT The periodontal pathogen Aggregatibacter actinomycetemcomitans produces a cytolethal distending toxin (Cdt) that inhibits the proliferation of oral epithelial cells. Structural models suggest that the CdtA and CdtC subunits of the Cdt heterotrimer form two putative lectin domains with a central groove. A region of CdtA rich in heterocyclic amino acids (aromatic patch) appears to play an important role in receptor recognition. In this study site-specific mutagenesis was used to assess the contributions of aromatic amino acids (tyrosine and phenylalanine) to receptor binding and CdtA-CdtC assembly. Predominant surface-exposed aromatic residues that are adjacent to the aromatic patch region in CdtA or are near the groove located at the junction of CdtA and CdtC were studied. Separately replacing residues Y105, Y140, Y188, and Y189 with alanine in CdtA resulted in differential effects on binding related to residue position within the aromatic region. The data indicate that an extensive receptor binding domain extends from the groove across the entire face of CdtA that is oriented 180° from the CdtB subunit. Replacement of residue Y105 in CdtA and residues Y61 and F141 in CdtC, which are located in or at the periphery of the groove, inhibited toxin assembly. Taken together, these results, along with the lack of an aromatic amino acid-rich region in CdtC similar to that in CdtA, suggest that binding of the heterotoxin to its cell surface receptor is mediated predominantly by the CdtA subunit. These findings are important for developing strategies designed to block the activity of this prominent virulence factor.

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