Purification of an alpha-L-fucoside-binding protein from Rhizobium lupini

Lectins associated with the bacterial cell surface of Rhizobium lupini strain LL13 were evidenced by erythrocyte agglutination, by aggregation of neoglycoprotein coated beads and by spectrofluorimetry using fluoresceinylated neoglycoproteins. At pH 5.0, a specific binding of the fluorescein-labelled neoglycoprotein bearing alpha-L-fucose was observed. The binding of this labelled neoglycoprotein is a saturable phenomenon and is inhibited by the same unlabelled neoglycoprotein. Extracts of R lupini obtained by disrupting a bacterial pellet through a French press were stabilized at pH 5.6 by gel filtration and purified to homogeneity by affinity chromatography on Agarose A4 substituted with alpha-L-fucose. A protein with a M(r) approximately 19,000 was specifically eluted from this affinity column with L-fucose. Isoelectric focusing of this sample yielded a single band with pI near 6.7. This protein specifically aggregated L-Fuc-BSA-coated microspheres. The results obtained in the present study indicate that we have purified from Rhizobium lupini strain LL13, a L-fucose binding protein as a lectin.

Plasmodium falciparum proteinases: cloning of the putative gene coding for the merozoite proteinase for erythrocyte invasion (MPEI) and determination of hydrolysis sites of spectrin by Pf37 proteinase

Numerous proteinase activities have been shown to be essential for the survival of Plasmodium falciparum. One approach to antimalarial chemotherapy, would be to block specifically one or several of these activities, by using compounds structurally analogous to the substrates of these proteinases. Such a strategy requires a detailed knowledge of the active site of the proteinase, in order to identify the best substrate for the proteinase. Aiming at developing such a strategy, two proteinases previously identified in our laboratory, were chosen for further characterization of their molecular structure and properties: the merozoite proteinase for erythrocytic invasion (MPEI), involved in the erythrocyte invasion by the merozoites, and the Pf37 proteinase, which hydrolyses human spectrin in vitro.

Dye-hydrophobic hapten conjugate/anti-dye antibody complex as immunogen: preparation of hydrophobic hapten-specific monoclonal antibodies

In order to induce the production of antibodies specific for small molecules, it is common to link them to a protein. However, when the small molecule is very hydrophobic it is extremely difficult to prepare such a conjugate. Here, we describe a simple way to obtain an antigenic conjugate under controlled conditions: in a first step a very hydrophobic hapten, cholanic acid, is linked to a dye, basilen blue, in organic solvent; in a second step the cholanic acid-basilen blue conjugate is dissolved in phosphate buffered saline and mixed with rabbit polyclonal anti-basilen blue antibodies previously raised in rabbits against basilen blue-key-hole limpet hemocyanin conjugate. Such a complex, which dissociates very slowly, appears to be a good immunogen in mice. Anti-cholanyl residue monoclonal antibodies were produced and characterized.

N-acetylglucosamine-binding proteins on Plasmodium falciparum merozoite surface

Plasmodium falciparum merozoite surface is specifically labelled with a neoglycoprotein bearing N-acetylglucosamine (GlcNAc) residues in a sugar-dependent manner, as shown by affinity cytochemistry in fluorescence and electron microscopy. To ascertain the nature of the sugar receptor, merozoite proteins were blotted and tested by a two-step method using biotinylated GlcNAc-bovine serum albumin (BSA) and streptavidin-peroxidase conjugate. Three parasite proteins were specifically revealed and designated as Pf 120, Pf 83 and Pf 45 GlcNAc-binding proteins. These proteins bind to a gel substituted with GlcNAc and are specifically eluted with 300 mM GlcNAc. Using a rabbit antiserum raised against Pf 83, the Pf 120 GlcNAc-binding protein, in addition to Pf 83, was labelled by Western blotting. Comparative analyses with an antibody against the Pf 83 MSP derived from the P. falciparum merozoite surface protein (Pf MSP) indicated that the Pf 83 GlcNAc-binding protein is not related to the fragment of the Pf MSP antigen. Similarly, the Pf 83 GlcNAc-binding protein is not related to the apical membrane antigen 1 (AMA 1) which also has the same molecular mass. Therefore the Pf 120, Pf 83 and Pf 45 GlcNAc-binding proteins which are located on the merozoite surface and recognize GlcNAc residues could be involved in the binding of merozoites to the glycoconjugates of the surface of the red blood cells.

Plasmodium falciparum proteinases and red blood cell invasion

Malarial proteinases of the erythrocytic life-cycle are used to design new inhibitors capable of blocking the parasite's development. The Merozoite Proteinase for Erythrocytic Invasion (MPEI) of Plasmodium falciparum, a neutral proteinase, and the acidic Pf37 proteinase acting on spectrin as substrate, are good candidates for this kind of strategy.

Sugar-dependent nuclear import of glycoconjugates from the cytosol

Large proteins (above 40 kDa) do not migrate from the cytosol to the nucleus except when they contain or are substituted with specific peptides called nuclear localization sequence. Accordingly fluorescein-labeled serum albumin, introduced into the cytosol upon electroporation, does not leave the cytosol. Conversely the same protein substituted with about 25 sugar residues migrate from the cytosol to the nucleus in a manner dependent on the nature of the sugar linked to serum albumin, on the temperature, and on the incubation time. Serum albumin substituted with glucose, fucose, or mannose residues enter the nucleus at 37 degrees C within 30 min while sugar-free serum albumin or serum albumin substituted with galactoside or 6-phosphomannoside residues do not. At 4 degrees C, all of those proteins stay in the cytosol. Thus, glycosylated proteins can enter the nucleus from the cytosol by making use of the sugars borne either by a new type of nuclear import or by making a complex with lectins acting as shuttle between cytosol and nucleus.

Sensitive, hydrosoluble, macromolecular fluorogenic substrates for human immunodeficiency virus 1 proteinase

Hydrosoluble macromolecular fluorogenic substrates specific for the human immunodeficiency virus 1 (HIV-1) proteinase have been prepared. The fluoresceinyl peptide Ftc-epsilon-Ahx-Ser-Phe-Asn-Phe-Pro-Gln-Ile-Thr-(Gly)n, corresponding to the first cleavage site of HIV-1 gag-pol native precursor was linked to a water-soluble neutral (Lys)n derivative. The epsilon-aminohexanoyl residue (epsilon-Ahx) and the glycyl sequence were added in order to improve the stability of the substrate and the accessibility of the cleavage site to the HIV-1 proteinase respectively. This macro-molecular peptidic-substrate conjugate is significantly more water-soluble than the free peptide itself on a substrate molar concentration basis. The assay is based on the quantitative precipitation of the polymeric material by adding propan-2-ol whereas the fluorescent peptide moiety released upon proteolysis remains soluble in the supernatant. The proteinase activity is assessed by measuring the fluorescence of the supernatant. This assay allows the detection of a few fmol of HIV-1 proteinase, even in the presence of cell culture media, plasma or cell lysate and it gives accurate results within a large proteinase concentration range. The hydrosoluble macromolecular substrate is also suitable for determining the HIV-1 proteinase activity using 96-well microplates, allowing us to test accurately and rapidly numerous enzyme samples and/or the potency of new proteinase inhibitors.

Specific gene transfer mediated by lactosylated poly-L-lysine into hepatoma cells

Plasmid DNA/glycosylated polylysine complexes were used to transfer in vitro a luciferase reporter gene into human hepatoma cells by a receptor-mediated endocytosis process. HepG2 cells which express a galactose specific membrane lectin were efficiently and selectively transfected with pSV2Luc/lactosylated polylysine complexes in a sugar dependent manner: i) HepG2 cells which do not express membrane lectin specific for mannose were quite poorly transfected with pSV2Luc/mannosylated polylysine complexes, ii) HeLa cells which do not express membrane lectin specific for galactose were not transfected with pSV2Luc/lactosylated polylysine complexes. The transfection efficiency of HepG2 cells with pSV2Luc/lactosylated polylysine complexes was greatly enhanced either in the presence of chloroquine or in the presence of a fusogenic peptide. A 22-residue peptide derived from the influenza virus hemagglutinin HA2 N-terminal polypeptide that mimics the fusogenic activity of the virus, was selected. In the presence of the fusogenic peptide, the luciferase activity in HepG2 cells was 10 fold larger than that of cells transfected with pSV2Luc/lactosylated polylysine complexes in the presence of chloroquine.

Oncogenes and expression of endogenous lectins and glycoconjugates

It is now well established that malignant transformation of eucaryotic cells is concomitant with typical alterations of glycosylation and the expression pattern of endogenous lectins. In parallel, oncogene transfection studies revealed a correlation between the expression of some of these genes, the transformed state and perhaps metastasis. These observations lead to the idea that oncogenes may control the expression of enzymes involved in the biosynthetic pathway of cell membrane glycoconjugates and the expression of endogenous lectins. Indeed, several contributions have shown that cells upon transfection with activated oncogenes of the ras family become invasive and/or metastatic and have their membrane glycoproteins modified. Information on the molecular mechanism of this postulated oncogene regulation is still lacking. Because of the diversity of the functions of oncogene-encoded proteins, further experiments dealing with other activated oncogenes may help in deciphering the regulation of expression of glycoconjugates and endogenous lectins together with their functions.

Characterization of membrane sugar-specific receptors in cultured high endothelial cells from mouse peripheral lymph nodes

The culture of specialized high endothelial cells (HEC) from lymphoid organs (peripheral lymph nodes (PLN) and Peyer's patches (PP)) was undertaken in order to study and characterize the cell surface molecules which are involved in lymphocyte recognition and allow homing. Cells were stimulated in vivo by a graft versus host (GVH) type of reaction before isolation and culture. The resulting adherent and growing cells were characterized as endothelial cells because of their typical aspect and their ability to produce angiotensin-converting enzyme and factor VIII-related antigen. They possess tissue-specific endothelial addressins. MECA 79 antigen is present on cells isolated from PLN while MECA 367 antigen is detected on cells from PP. Surface receptors for glycans were studied cytochemically using neoglycoproteins and fluorescence microscopy and quantified by flow cytometry experiments which showed that the specificity of sugar receptors depends upon endothelial cell origin. Indeed, sugar receptors for alpha-L-fucosyl residues were specifically expressed by endothelial cells from PLN. These receptors were inducible upon action of activated lymphocyte-conditioned medium. Further characterization of endothelial cells from peripheral lymph nodes indicates that they indeed mediate adhesion of lymphocytes in vitro. The role of protein-sugar interactions in this process was assessed by inhibition experiments performed with the help of neoglycoproteins. Best inhibitory effects were obtained when endothelial cells had been preincubated with alpha-L-fucosyl-BSA and when lymphoid cells were preincubated with beta-D-galactosyl-BSA. Concomitant inhibition assays indicate the participation of sugar specific receptors--endogenous lectins--on the surface of both endothelial and lymphoid cells to achieve recognition and adhesion.

Endocytosis of alpha 1-acid glycoprotein variants by human monocytic lineage cells

Human alpha 1-acid glycoprotein (AGP or orosomucoid) is a major glycoprotein of plasma. AGP can be separated on immobilized concanavalin A into three variants bearing none (AGP A), one (AGP B) or two (AGP C) biantennary glycans. In this paper, we show, using flow cytometry and confocal microscopy, that AGP C which is eluted from concanavalin A with mannose, binds to human monocytes, monocyte-derived macrophages as well as human promonocytic cell lines such as THP1 or U937. Conversely HL60, a promyelocytic cell line, does not express the surface AGP C binding protein. AGP C is internalized and degraded with an efficiency depending on the state of differentiation of these cells. In contrast, AGP A which is not recognized by concanavalin A, does not bind to any of these cells.

A SV-40 immortalized murine endothelial cell line from peripheral lymph node high endothelium expresses a new alpha-L-fucose binding protein

Endothelial cells from mouse peripheral lymph nodes were immortalized by cationic liposome-mediated transfection using a plasmid construct containing both the gene coding for the large T antigen of simian virus 40 and a geneticin resistance gene suitable for selection. A cell line (HECa10) was isolated on the basis of its capacity to specifically bind fucoside carrying glycoconjugates; these cells present the main characteristics of endothelial cells: production of angiotensin converting enzyme and of factor VIII-related antigen. Upon stimulation, they express E-selectin which binds oligosaccharides containing the Lewisx determinant (Fuc alpha 3[Gal beta 4 GlcNAc beta 3Gal beta) and the MECA 79 addressin which is characteristic for the peripheral lymph node high endothelium and is a L-selectin ligand. HECa10 cells, as well as peripheral lymph node high endothelial cells in primary culture, express a second fucoside binding protein which differs from E-selectin. Indeed, this new fucoside-binding protein is constitutively expressed on unstimulated cells while E-selectin is not. Furthermore, HECa10 cells mediate selective lymphoid cell adhesion in a selectin/addressin-dependent mechanism, mainly inhibited by MECA 79 antibody and, in a fucose-binding lectin-dependent manner, mainly inhibited by the specific neoglycoprotein.

C32 human melanoma cell endogenous lectins: characterization and implication in vesicle-mediated melanin transfer to keratinocytes

To optimize skin pigmentation in order to help body prevention against UV radiation, the mechanism of melanin pigment transfer from melanocytes to keratinocytes must be elucidated. Melanin transfer to keratinocytes requires specific recognition between keratinocytes and melanocytes or melanosomes. Cell surface sugar-specific receptor (membrane lectin) expression was studied in human C32 melanoma cells, an amelanotic melanoma, by flow cytometry analysis of neoglycoprotein binding as an approach to the molecular specificity. Sugar receptors on melanocytes are mainly specific for alpha-L-fucose. Their expression is enhanced upon treatment by the diacylglycerol analogue 1-oleoyl-2-acetylglycerol, which can induce melanin synthesis in amelanotic human melanoma cells in a dose-dependent manner. Flow cytometry analyses showed a small-sized population of vesicles distinguishable from large cells by their fluorescence properties upon neoglycoprotein binding. Sorting indicated that the small-sized subpopulation is composed of vesicles produced by melanocytic cells. Upon vesicle formation, a selective concentration of sugar receptors specific for 6-phospho-beta-D-galactosides appears in the resulting melanocytic vesicles. Vesicles are recognized and taken up by cultured keratinocytes and a partial inhibitory effect was obtained upon cell incubation in the presence of neoglycoproteins, indicating a possible participation of sugar receptors in this recognition. The validity for such a model to help in understanding the natural melanin transfer by melanosomes is confirmed by electron microscopy, which demonstrates the presence of melanin inside keratinocytic cells upon incubation with melanocytic vesicles.

Antileishmanial drug targeting through glycosylated polymers specifically internalized by macrophage membrane lectins

Antileishmanial chemotherapy is hampered by the location of the parasite within the phagolysosome of the macrophage, which restricts the bioavailability of many potentially useful antileishmanial drugs. In this study, the possibility of using antileishmanial drugs targeted to the infected macrophages by means of a chemical linkage to a neutral mannose-substituted poly-L-lysine carrier molecule was explored. The study was performed in an in vitro model with Leishmania donovani-infected murine macrophages. The antileishmanial activities of various synthetic constructs were compared with those of the free drugs and the pentavalent antimonial Pentostam, which was used as the positive control. The 50% effective dose of allopurinol riboside linked to the mannosylated poly-L-lysine was below 7.5 x 10(-6) M, while it was up to 3 x 10(-4) M for the free drug, indicating that the drug bound to the polymer was 50 times more active than the free drug. Control experiments with other constructs (e.g., allopurinol riboside linked to the mannose-free polymer) confirmed that the enhancement of activity was indeed achieved by means of the mannose homing device.

Drug targeting: synthesis and endocytosis of oligonucleotide-neoglycoprotein conjugates

Inhibition of gene expression by antisense oligonucleotides is limited by their low ability to enter cells. Knowing that sugar binding receptors, also called membrane lectins, efficiently internalize neoglycoproteins bearing the relevant sugar, 6-phosphomannose, for instance, oligonucleotides--substituted on their 5'-end with either a fluorescent probe or a radioactive label on the one hand, and bearing a thiol function on their 3'-end, on the other hand,--were coupled onto 6-phosphomannosylated proteins via a disulfide bridge. The oligonucleotide bound to 6-phosphomannosylated serum albumin is much more efficiently internalized roughly 20 times than the free oligonucleotide. Although most of the oligonucleotides are associated with vesicular compartments, oligonucleotides after releasing from the carrier by reduction of the disulfide bridge may find their way to reach the cytosol and then lead to an increase in the efficiency of the oligonucleotides.

Uptake by macrophages of a biotinylated oligo-alpha-deoxythymidylate by using mannosylated streptavidin

Streptavidin substituted with mannose residues increased by 20-fold the intracellular concentration of a biotinylated dodecakis(alpha-deoxythymidylate) in macrophages by comparison with the uptake of free oligodeoxynucleotide. Streptavidin, the bacterial homologue of the very basic avidin, which does not contain any carbohydrate moieties and is a neutral protein, was substituted with 12 mannose residues in order to be recognized and internalized by mannose-specific lectins on the surface of macrophages. A 3'-biotinylated and 5'-fluoresceinylated dodecakis (alpha-deoxythymidylate) was synthesized and bound onto mannosylated streptavidin. The conjugate was isolated, and by using flow cytometry, it was shown that the uptake of fluoresceinylated oligodeoxynucleotides bound to mannosylated streptavidin by macrophages is 20-fold higher than that of free oligodeoxynucleotides and that the uptake was competively inhibited by mannosylated serum albumin. Glycosylated streptavidin conjugates recognizing specific membrane lectins on different cells provide the possibility to target biotinylated antisense oligodeoxynucleotides and to increase the biological effect of these chemotherapeutic agents.

Purification of a glucose-binding protein from rat liver nuclei. Evidence for a role in targeting of nuclear mRNP to nuclear pore complex

A nuclear carbohydrate-binding protein with a molecular mass of 67 kDa (CBP67), which is specific for glucose residues, was purified to essential homogeneity from rat liver nuclear extracts. This protein could also be isolated from nuclear ribonucleoprotein (RNP) complexes by extraction in the presence of 0.6 M or 2 M NaCl, but it was absent in polysomal RNP complex. The binding of the purified protein, which has an isoelectric point of 7.3, to glucose-containing glycoconjugates depends on the presence of Ca2+ and Mg2+. Using closed nuclear envelope vesicles as a system to study nuclear transport of RNA, it was shown that both entrapped polysomal mRNA and nuclear RNA precursors are readily exported from the vesicles in an ATP-dependent manner. The transport was unidirectional and strongly promoted by the poly(A) segment attached to these RNAs. In contrast, nuclear RNP complexes entrapped into the vesicles together with glucose-conjugated bovine serum albumin or nucleoplasmin, or bird nest glycoprotein, were not exported into the extravesicular space. However, transport of nuclear RNP complexes could be achieved in the presence of glucose or after co-addition of a glucose-recognizing lectin from Pellina semitubulosa. In Western blots, radioiodinated CBP67 binds to an 80-kDa polypeptide both in isolated rat liver nuclear envelopes and pore-complex laminae. From these results we postulate that CBP67 may direct nuclear RNP complexes to the nuclear pore.

Activation of mouse macrophages by muramyl dipeptide coupled with an anti-macrophage monoclonal antibody

A rat IgG2a monoclonal antibody (mAb3A33) directed against the mouse Mac-1 antigen was conjugated with muramyl dipeptide (MDP) by using an intermediate polymer; under such conditions 75 MDP molecules were bound to one antibody molecule. A poly(L-lysine) polymer substituted with muramyl dipeptide and 3-(2-pyridyldithio)propionyl residues were prepared, the remaining lysine epsilon-amino groups were acylated with D-gluconolactone, leading to a neutral polymer; then a few polymer conjugates were coupled to mAb3A33 via a disulfide bridge. The binding capacity of the monoclonal antibody was preserved after conjugation with MDP-polymer molecules. Mouse peritoneal macrophages, incubated for 24 h with MDP-mAb3A33 conjugate became cytostatic against P815 mastocytoma cells, whereas unconjugated mAb3A33 and MDP-bound to a nonspecific rat IgG2a were ineffective. An enhancement of the cytostatic activity induced by MDP-mAb3A33 conjugate was obtained in the presence of gamma-IFN. These results show that several tens of MDP molecules can be linked to a macrophage-specific monoclonal antibody by using a neutral intermediate polymer without impairing the binding antibody capacity and that this type of MDP conjugate can efficiently activate macrophages and therefore could be the basis of the development of new antitumor therapy.

Characterization of two galactosidases extracted from wheat germ with a hydroalcoholic solvent

Alpha- and beta-D-galactosidases were characterized from a hydroalcoholic extract of wheat germ (Triticum vulgare). Kinetic constants (Vmax and KM) and the optimal pHs for the hydrolysis of p-nitrophenyl galactopyranosides by both enzymes were determined. These enzymes presented a high stability in hydroalcoholic medium and were inhibited by iodoacetamide and sodium p-hydroxy-mercuribenzoate.

Characterization of an Agrobacterium tumefaciens lectin

An Agrobacterium tumefaciens suspension induces a strong agglutination of aldehyde-fixed pig erythrocytes at pH 5.0. The agglutination is inhibited by some polysaccharides, such as fucoidin, and also when the pH is raised to 7.0. Lectins (sugar-binding proteins) associated with the bacterial cell wall of A. tumefaciens strain 84.5 were directly evidenced by spectrofluorimetry using fluoresceinylated neoglycoproteins. The specific binding of the fluorescein-labelled neoglycoprotein bearing alpha-L-fucoside residues was also optimal at pH 5.0. A lectin was purified by affinity chromatography on agarose substituted with alpha-L-fucopyranoside. Furthermore, the haemagglutination activity of this lectin was inhibited by polysaccharides isolated from poplar leaves.

Water-soluble macromolecular fluorogenic substrates for assaying proteinases: determination of pancreatic elastase activity

Water-soluble macromolecular fluorogenic substrates were synthesized in order to develop an easy specific proteinase assay. The validity of this method was tested with porcine pancreatic elastase by using its specific peptidic substrate Ala-Ala-Pro-Ala linked to a hydrosoluble polymer. The octapeptidic sequence FTC-epsilon Aca-Ala-Ala-Pro-Ala-Gly-Gly-Gly was linked to a water-soluble and neutral poly-L-lysine derivative. The aminocaproyl residue and the triglycyl sequence were added in order to improve the stability of the substrate, and the accessibility of the specific sequence Ala-Ala-Pro-Ala to elastase, respectively. The assay is based on the quantitative precipitation of the polymeric substrate in isopropanol while the released soluble fluorescent peptidic moiety is fluorometrically titrated in the supernatant.

Peptide derivatives specific for a Plasmodium falciparum proteinase inhibit the human erythrocyte invasion by merozoites

A specific proteinase of P. falciparum merozoites has been detected by using hydrosoluble fluorogenic peptidic substrates synthesized by classical peptide chemistry; their N-terminal end was acylated by a gluconoyl group that protects them from aminopeptidase degradation and increases their hydrosolubility, and their carboxylic end was substituted by a 3-amino-9-ethylcarbazole group. The sequence Val-Leu-Gly-Lys was found to be the most specific substrate. On this basis, reversible peptidic inhibitors were synthesized by substituting the C-terminal lysyl residue, at the proteolytic site, by different alkylamines and amino alcohols. The activity of these compounds, studied on the P. falciparum proteinase and in in vitro cultures, strongly suggests a specific effect of this peptidic sequence on the reinvasion process. The peptidic inhibitors do not impair the release of merozoites from schizonts, but selectively inhibit the invasion step leading to the formation of rings. Although the natural target of this enzyme is not yet known, these specific peptide inhibitors could lead to a new antimalarial approach.

Changes in the expression of lectins in human T lymphocyte membrane upon mitogenic stimulation

Surface lectins, specific for given sugar structures, are expressed on human T cells, as shown by flow cytofluorometry using F-neoglycoproteins bearing either beta- and alpha-D-galactosyl, beta-D-galactosyl 6-phosphate, or alpha-L-rhamnosyl groups, but not by F-neoglycoproteins bearing other sugar groups (such as alpha-D-mannosyl groups). After stimulation with Phaseolus vulgaris mitogen, the number of cells that bind beta-D-galactosyl 6-phosphate groups (6-P-beta-D-Galp lec+ cells) increased fourfold during the first five days; these cells are helper (CD4+) T cells. Conversely, cells that bind alpha-L-Rha groups belong to the T suppressor (CD8+) family and their number moderately increased. Upon stimulation by concanavalin A, the number of cells expressing the lectin recognizing alpha-L-Rha groups increased during the first two days and then decreased within the next two days. These results are discussed with regard to the implication of lymphocyte membrane lectins in the suppressor mechanism and in the homing process.

Characterization and isolation of an intracellular D-mannose-specific receptor from human promyelocytic HL60 cells

Most mammalian macrophages express D-mannose-specific receptor (membrane lectin, Mr 175,000) allowing endocytosis of their ligands, but cells of the monocytic lineage (HL60, U937, monocyte) lack this receptor. However, after permeabilization, promyelocytic, promonocytic cells and monocytes bound fluoresceinylated D-mannose-terminated neoglycoproteins as evidenced by flow cytometry. Under these conditions, confocal analysis confirmed the intracellular membrane localization of the labeling and the absence of nuclear binding. An intracellular D-mannose-specific receptor was isolated from the human promyelocytic cell line HL60, by affinity chromatography on 4-isothiocyanatophenyl alpha-D-mannopyranoside-substituted Affi-gel as a 60,000-Mr membrane protein requiring divalent cations for the ligand binding. Under the same conditions, mouse macrophages were shown to express a 175,000-Mr D-mannose-specific receptor but not the 60,000-Mr receptor.