S layer protein of Clostridium tetani: purification and properties.

S layer protein of Clostridium tetani strain AO 174, a nontoxigenic derivative of strain Harvard A 47, was prepared from the cell walls by 4 M urea extraction and purified by DEAE-Sepharose CL-6B chromatography followed by a combination of anion-exchange chromatography and reverse-phase chromatography using an HPLC system. The molecular weight of the S layer protein was estimated to be 140 kilodaltons (kDa) by SDS-PAGE. The amino acid composition of the 140 kDa protein was very similar to those of S layer proteins from the other bacterial species: it was rich in acidic amino acid and lacked cysteine. Also, the protein was unique in its extremely low content of proline (0.02 to 0.03 mol%). Multiple isoelectric forms ranging from pH 4.0 to 4.5 were observed in the purified preparation. Immunodiffusion analysis showed that the 140 kDa protein was a common antigen to the three strains of C. tetani tested.     

Isoelectric point of an ion-penetrable membrane.

The surface potential of an ion-penetrable planar membrane is calculated for the case in which acidic and basic groups are present in the membrane. It is found that when both acidic and basic groups are not uniformly distributed in the direction normal to the membrane, the isoelectric point (the pH value at which the surface potential becomes zero) of the membrane varies with the electrolyte concentration, whereas if both groups are uniformly distributed, the isoelectric point is independent of the electrolyte concentration. As a simple example, we treat a membrane consisting of two layers, in which acidic groups are distributed in the outer layer and basic groups are in the inner layer. Simple equations determining the membrane surface potential as a function of pH and electrolyte concentration and the dependence of the isoelectric point on the electrolyte concentration are presented.     

Purification and characterization of S layer proteins from Clostridium difficile GAI 0714

The S layer of Clostridium difficile GAI0714 was shown to be composed of two proteins, of 32 kDa and 45 kDa, as determined by SDS-PAGE. The two proteins were extracted with 8 M-urea (pH 8.3) from a cell wall preparation and purified by DEAE-Sepharose CL-6B chromatography followed by HPLC gel filtration. When solubilized in 0.1 M-urea, both proteins appeared to exhibit dimeric forms, with respective molecular masses of about 61 kDa and 99 kDa, upon HPLC. Although the amino acid compositions of the two proteins differed from each other, both proteins had a high content of acidic amino acids, very low contents of histidine and methionine, and no cysteine. The 32 kDa protein exhibited multiple isoelectric forms (pI 3.7-3.9), whereas the 45 kDa protein had a single form (pI 3.3). Radioiodination and immunogold labelling revealed that both proteins were exposed evenly over the entire cell surface. Based on immunodiffusion analysis using monospecific antiserum raised to the individual proteins, there was no antigenic relationship between the two proteins. Furthermore, immunoblot analysis showed that the antigenicity of the 32 kDa protein appeared to be strain specific, whereas that of the 45 kDa protein appeared to be group specific.     

Electrochemical modification of vesicular stomatitis virus glycoprotein by host cell transformation

Electrochemical properties of the glycoprotein of vesicular stomatitis virus (VSV) grown in Rous sarcoma virus (RSV)-transformed cells was compared with that of its counterpart grown in nontransformed cells. In DEAE-Sephadex column chromatography, the glycoproteins of VSV derived from transformed cells appeared more heterogeneous and had a tendency to elute with higher concentrations of NaCl than those from nontransformed cells. In isoelectric focussing, the glycoproteins of VSVs derived from transformed and nontransformed cells appeared as multiple components differing in the isoelectric point, and the glycoproteins from virus from transformed cells had isoelectric points that were more acidic than their counterparts from nontransformed cells. These results show that the glycoprotein of VSV consists of populations of molecules differing in charge and their isoelectric points were shifted to the acidic side by host cell transformation.     

Fine structure and histochemistry of the epidermis of the fish Monopterus cuchia

An attempt is made to correlate fine structure with the histochemical reactions of the epidermis in the synbranchiform fish Monopterus cuchia. Three sources of mucus are identified. Superficial epithelial cells produce weakly acidic glycoprotein which is secreted at the surface as the external mucous layer or cuticle. Numerous large unicellular mucous glands have a secretion which is strongly acidic and sulphated, although the basal and peripheral parts of these cells, which contain most of the rough endoplasmic reticulum, react strongly for neutral glycoprotein; Golgi cisternae appear to be involved in a change of histochemical reaction from neutral to strongly acidic as the secretion is formed. A second, slender, type of mucous gland cell, not previously reported, gives a weaker reaction for sulphated acidic glycoprotein and has cytoplasm with numerous Golgi cisternae and free ribosomes, producing electron–dense secreted drops. Sacciform cells, with a protein–aceous secretion, have a characteristic fine structure with membranous "bubbles" at the surface of the cytoplasm. Ionocytes, sensor) cells and intrusive leucocytes have been identified in the epidermis.     

Characterization of neutrophil alkaline phosphatase-inducing factor (NAP-IF)

A factor, termed neutrophil alkaline phosphatase-inducing factor (NAP-IF), that has the capacity to increase the NAP activity of granulocytes was characterized by using two samples: cystic fluid (CF) and conditioned medium of a tumor cell line (T3M5). The molecular weight of NAP-IF was shown to be between 13,000 and 45,000, and its isoelectric point was between 5.5 and 6.2. It was sensitive to heat and proteolytic enzymes, but was resistant to DNase and RNase, suggesting that NAP-IF is an acidic protein or glycoprotein. These characteristics of NAP-IF seem to be similar to those of granulocyte-macrophage colony-stimulating factor (GM-CSF) that is also present in the CF. NAP-IF rich fractions obtained by isoelectric focusing from CF were also found to be rich in a subclass of GM-CSF: granulocyte-CSF (G-CSF). Furthermore, a high correlation was noted between the activities of G-CSF and NAP-IF (gamma = 0.798, P less than 0.005). These results suggest that the two activities, i.e., G-CSF and NAP-IF, may be attributable to an identical macromolecule.     

Characterization of the surface layer glycoprotein of Clostridium symbiosum HB25.

The cell surface of Clostridium symbiosum HB25 is covered by a squarely arranged surface layer (S-layer) glycoprotein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the sodium dodecyl sulfate-soluble whole-cell extract showed the presence of several high-molecular-weight protein bands in a narrow range (approximate Mr, 140,000) which, upon periodic acid-Schiff staining, gave a positive reaction. After proteolytic degradation of the purified S-layer glycoprotein, a single glycopeptide fraction was obtained by gel permeation chromatography. Hydrolysis, treatment with aqueous hydrofluoric acid, and 1H and 13C nuclear magnetic resonance studies showed that the glycoprotein glycan is a high-molecular-weight polymer (approximate Mr, 15,000) of tetrasaccharide repeating units with the component sugars N-acetylgalactosamine (GalNAc), N-acetylmannosamine (ManNAc), and N-acetylbacillosamine (BacNAc; 2-N-acetyl-4-amino-2,4,6-trideoxy glucose) linked by monophosphate diesters. The following structure is proposed: [----6)-alpha-D-ManpNAc-(1----4)-beta-D-GalpNAc-(1----3)-alpha-D-+ ++BacpNAc- (1----4)-alpha-D-GalpNAc-(1----PO3)----]n. The nuclear magnetic resonance data provided evidence for a charge interaction between the free amino group of BacNAc and the phosphate group of adjacent glycan chains. Since polycationic ferritin did not label the cell surface of intact cells, an electrostatic interaction can also be expected in vivo, leading to a charge-neutral outer surface, which is characteristic of all other S layers from members of the family Bacillaceae studied so far.     

Specific Lectin Binding to Beta1 Integrin and Fibronectin on the Apical Membrane of Madin-Darby Canine Kidney Cells

Although lectins have previously been used to identify specific cell types in the kidney and various other tissues, the proteins labeled were not identified. We hypothesized that fluorescently labeled lectins could provide a useful tool for direct labeling of membrane-associated glycoproteins. Protein fractions from Madin-Darby canine kidney (MDCK) cells were exposed to a panel of 16 fluorescently labeled lectins to identify suitable lectin-protein pairs. Peanut agglutinin (PNA) selectively bound a 220-240 kDa O-linked glycoprotein with a slightly acidic isoelectric point, while Sambucus nigra agglutinin (SNA) labeled a 130 kDa glycoprotein with a highly acidic isoelectric point. Both proteins were readily labeled by lectins applied to the apical surface of living confluent cells. The proteins were isolated by lectin affinity columns and identified by mass spectrometry. Peptides from the PNA-binding protein shared molecular weight and amino acid composition with fibronectin. Fragments of the SNA-binding protein showed amino-acid identity with peptides from beta1 integrin. The identities of these proteins were validated by Western blotting. Binding of PNA to a 220 kDa protein was inhibited by an anti-fibronectin antibody, and binding of a 130 kDa protein by SNA was diminished by an anti-beta1 integrin antibody. We conclude that PNA and SNA can be used as specific markers for fibronectin and beta1 integrin, respectively, in MDCK cells.     

Structure of the glycan chain from the surface layer glycoprotein of Clostridium thermohydrosulfuricum L77-66.

The thermophilic eubacterium Clostridium thermohydrosulfuricum L77-66 is covered by a crystalline surface layer composed of identical glycoprotein subunits which are arranged in a hexagonal lattice with centre-to-centre spacings of approx. 14.3 nm. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of cell wall preparations showed the presence of several broadened, carbohydrate-containing bands in a molecular mass range of 90 to 200 kDa. A total carbohydrate content of approx. 14% was determined in the purified surface layer glycoprotein. Chemical deglycosylation of this material by trifluoromethanesulfonic acid resulted in the disappearance of the complex banding pattern. Only a single band with a molecular mass of 82 kDa remained visible upon Coomassie staining. After proteolytic digestion of the surface layer glycoprotein a single glycopeptide fraction with an apparent molecular mass of approx. 25 kDa was obtained by gel filtration. Composition analysis, methylation, periodate oxidation and a combination of homonuclear and 1H-detected heteronuclear shift-correlated nuclear magnetic resonance experiments established the following structure for the glycan chain of the surface layer glycoprotein.     

Demonstration and characterization of the cell wall carbohydrate and protein antigens from Clostridium botulinum type E Saroma

Two different cell wall antigens, carbohydrate (CHO) and protein (P), from Clostridium botulinum type E Saroma were extracted with sodium dodecyl sulfate (SDS) and purified by chromatography on DEAE-Sepharose CL-6B and Sephadex G-75 or G-100. The CHO antigen was composed of glucose, galactose, glucosamine, galactosamine, alanine and phosphorus with a molar ratio of 1.5:1.5:0.25:0.25:1:1. The P antigen was an acidic protein with a molecular weight of 60 kDa, in which the major amino acids were aspartate, glutamate and serine, while the minor ones were cysteine and methionine. Thin sections of the intact or SDS-extracted cells of the organism demonstrated that the cell wall was composed of a two-layered structure, an inner layer about 20 nm thick and an outer layer about 10 nm, and by the extraction with SDS, the outer layer disappeared from the cell surface, leaving the inner layer. Immunogel diffusion tests demonstrated that either CHO antigen or P antigen was common among the nonproteolytic strains of C. botulinum.     

Structural analysis of precursor and product forms of type-common envelope glycoprotein D (CP-1 antigen) of herpes simplex virus type 1.

The type-common CP-1 antigen of herpes simplex virus type 1 (HSV-1) is associated in the infected cell with two components, a 52,000-molecular-weight glycoprotein (gp52 or pD) and a 59,000-molecular-weight glycoprotein (gp59 or D). The larger form (D) is also found in the virion envelope. It was postulated that pD is a precursor of D. We found that pD shared methionine and arginine tryptic peptides with D isolated from infected cell extracts. D isolated from infected extracts had the same trypric methionine peptide profile as D isolated from the virion envelope. Thus, processing of pD to D does not involve any major alterations in polypeptide structure. Furthermore, D did not share tryptic methionine peptides with the other major glycoproteins of HSV-1. Using [2-3H]mannose as a specific glycoprotein label, we found that pD, which is a basic protein (isoelectric point = 8.0) contained a 1,800-molecular-weight oligomannosyl core moiety and was processed by further glycosylation and sialyation to a more acidic and heterogeneous molecule D, which as a molecular weight of at least 59,000.     

Characterization and Ultrastructural Localization of Chitinases from Metarhizium anisopliae, M. flavoviride, and Beauveria bassiana during Fungal Invasion of Host (Manduca sexta) Cuticle

Extracellular chitinases have been suggested to be virulence factors in fungal entomopathogenicity. We employed isoelectric focusing and a set of three fluorescent substrates to investigate the numbers and types of chitinolytic enzymes produced by the entomopathogenic fungi Metarhizium anisopliae, Metarhizium flavoviride, and Beauveria bassiana. Each species produced a variety of N-acetyl-(beta)-d-glucosaminidases and endochitinases during growth in media containing insect cuticle. M. flavoviride also produced 1,4-(beta)-chitobiosidases. The endochitinases could be divided according to whether they had basic or acidic isoelectric points. In contrast to those of the other two species, the predominant endochitinases of M. anisopliae were acidic, with isoelectric points of about 4.8. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved the acidic chitinases of M. anisopliae into two major bands (43.5 and 45 kDa) with identical N-terminal sequences (AGGYVNAVYFY TNGLYLSNYQPA) similar to an endochitinase from the mycoparasite Trichoderma harzianum. Use of polyclonal antibodies to the 45-kDa isoform and ultrastructural immunocytochemistry enabled us to visualize chitinase production during penetration of the host (Manduca sexta) cuticle. Chitinase was produced at very low levels by infection structures on the cuticle surface and during the initial penetration of the cuticle, but much greater levels of chitinase accumulated in zones of proteolytic degradation, which suggests that the release of the chitinase is dependent on the accessibility of its substrate.     

Cellular localization and substrate specificity of isoelectric forms of human liver neuraminidase activity.

The four major isoelectric forms of human liver neuraminidase (with pI values between 3.4 and 4.8) have been isolated by preparative isoelectric focusing and characterized with regard to their substrate specificity using glycoprotein, glycopeptide, oligosaccharide and ganglioside natural substrates. All forms exhibited a rather broad linkage specificity and were capable of hydrolyzing sialic acid glycosidically linked alpha 2-3, alpha 2-6 and alpha 2-8, although differential rates of hydrolysis of the substrates were found for each form. The most acidic form 1 (pI 3.4) was most active on sialyl-lactose, whereas form 2 (pI 3.9) and 3 (pI 4.4) were most active on the more hydrophobic ganglioside substrates. Form 4 (pI 4.8) was most active on the low-Mr hydrophilic substrates (fetuin glycopeptide, sialyl-lactose). Each form was less active on the glycoprotein fetuin than on a glycopeptide derived from fetuin. Organelle-enriched fractions were prepared from fresh human liver tissue and neuraminidase activity on 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid was recovered in plasma membrane, microsomal, lysosomal and cytosolic preparations. Isoelectric focusing of the neuraminidase activity recovered in each of these preparations resulted in significantly different isoelectric profiles (number, relative amounts and pI values of forms) for each preparation. The differential substrate specificity of the isoelectric forms and the different isoelectric focusing profiles of neuraminidase activity recovered in subcellular-enriched fractions suggest that specific isoelectric forms with broad but defined substrate specificity are enriched at separate sites within the cell.     

Isolation, characterization, and in vitro assembly of the tetragonally arrayed layer of Bacillus sphaericus.

The tetragonally arranged cell wall layer (T-layer) of Bacillus sphaericus NTCC 9602 was isolated and characterized. Parallel studies were made on a spontaneous variant of the wild-type strain which had a T-layer subunit of altered molecular weight. A purification method for the T-layers was devised which involved separation of the cell walls from the cytoplasmic contents, urea dissociation of the T-layer from the cell walls, removal of soluble contaminants by differential centrifugation, and finally selective adsorption of uncleaved subunits to sacculi. The purified subunits retained the capacity to form an assembly in vitro with the same lattice parameters as that observed on whole cells or cell walls and could readsorb to the cell walls from which they had been extracted. Both the wild-type and the variant subunits behaved as single, homogeneous polypeptide chains. Carbohydrate assay and isoelectric point determinations revealed that both subunit types were acidic glycoproteins. Values obtained for thebuoyant density, isoelectric point, and extinction coefficient differed minimally; major differences were observed in the molecular weight and the characterisitc width of cylinders formed by in vitro-assembled T-layer of the wild-type and variant. Assembled T-layer was subject to alkaline or acid dissociation and in acid titration dissociated at its isoelectric point.     

Characterization of a novel ZP3-independent sperm-binding ligand that facilitates sperm adhesion to the egg coat

During mammalian fertilization, sperm adhere to the extracellular coat of the egg, or zona pellucida, in a species-specific manner. In mouse, evidence suggests that sperm recognize and bind to specific oligosaccharide ligands within the zona pellucida glycoprotein, ZP3, via beta1,4-galactosyltransferase I (GalT I), a lectin-like receptor on the sperm surface. Although in vitro experiments using isolated gametes lend support to this model, recent in vivo studies of genetically altered mice question whether ZP3 and/or GalT I are solely responsible for sperm-egg binding. In this regard, sperm from GalT I-null mice bind poorly to ZP3 and fail to undergo a zona-induced acrosome reaction; however, they still bind to the ovulated egg coat in vitro. In this report, we characterize a novel ZP3- and GalT I-independent mechanism for sperm adhesion to the egg coat. Results show that the ovulated zona pellucida contains at least two distinct ligands for sperm binding: a ZP3-independent ligand that is peripherally associated with the egg coat and facilitates gamete adhesion; and a ZP3-dependent ligand that is present in the insoluble zona matrix and is recognized by sperm GalT I to facilitate acrosomal exocytosis. The ZP3-independent ligand is not a result of contamination by egg cortical granules, nor is it the mouse homolog of oviduct-specific glycoprotein. It behaves as a 250 kDa, WGA-reactive glycoprotein with a basic isoelectric point, distinguishing it from the acidic glycoproteins that form the insoluble matrix of the egg coat. When eluted from isoelectric focusing gels, the acidic matrix glycoproteins possess sperm-binding activity for wild-type sperm, but not for GalT I-null sperm, whereas the basic glycoprotein retains sperm-binding activity for both wild-type and GalT I-null sperm. Thus, GalT I-null sperm are able to resolve gamete recognition into at least two distinct binding events, leading to the characterization of a novel, peripherally associated, sperm-binding ligand on the ovulated zona pellucida.     

Effect of BYDV Infection on the Cell Surface Glycoproteins in Common Wheat,Wheatgrass and Octoploid Wheat-Wheatgrass

Changes in the cell surface glycoproteins in common wheat 3B-2, Agropyron intermedium and octoploid wheat-wheatgrass Zhong 5 after the inoculation with barley yellow dwarf virus (BYDV) were sdudied using electron microscopy and ruthenium red staining. The results indicated that, after the inoculation with BYDV, different changes in cell surface glycoproreins were observed in the plant species with different levels of resistance. In A. intermediurn which is immune to BYDV, inoculation with BYDV did not cause significant change in cell surface glycoprotein layer. In cotoploid wheat-wheatgrass Zhong 5 which is highly resistent to BYDV, BYDV infection caused significant thickening in most cell surface glycoprotein layer. In common wheat 3B-2 which is susceptible to BYDV, BYDV infection did not cause thickening in cell surface glycoprotein layer, but in most cells, glycoproteins on the cell surface were partially peeled off or disappeared completely. Therefore, it is suggested that the glycoproteins on cell surface play certain roles in BYDV resistance. The phenomenon of the thickening of cell surface glycoprotein layer caused by BYDV infection was possibly a resistant reaction to the virus.     

Electron microscope observations on the carbohydrate-rich cell coat present at the surface of cells in the rat

Periodic acid-silver methenamine, a fairly specific technique for glycoprotein detection, was used to stain a variety of rat tissues, in the hope of confirming the existence of a carbohydrate-rich "cell coat" at the surface of mammalian cells. It was found that nearly all cells are coated by a thin layer of stained material. Around fibrocytes and migrating blood cells, the layer is uniform and merges with the ground substance. In the nervous system, cells and processes are surrounded with a layer whose density increases in synaptic clefts. Around epithelial cells, the layer outlines apical microvilli, follows lateral interspaces, and extends between cells and basement membrane. The layer is continuous with the middle plate of desmosomes and can be followed within the wide portion of terminal bars. In contrast, staining usually vanishes when two adjacent plasma membranes fuse to form tight junctions. These findings indicate that the stained layer is a "cell coat" located outside the plasma membrane. Since the cell coat is also stained by colloidal thorium, a technique for detection of acidic carbohydrates, this structure presumably contains not only glycoprotein(s) but also acidic residues. The carbohydrates may play a role in holding cells together and in controlling the interactions between cells and environment.     

Cloning of a recombinant complementary DNA to a baboon (Papio anubis) estradiol-dependent oviduct-specific glycoprotein.

The estradiol-dominated baboon oviduct synthesizes and secretes a glycoprotein (mol wt, 120,000) that binds to oocyte zona pellucida in vivo. This glycoprotein separates into two major isoelectric variants (pl 8.0 and 4.5) on two-dimensional electrophoretic gels. This study was undertaken to further characterize the steroid-controlled gene expression of this glycoprotein. A recombinant cDNA library was prepared to poly(A)+ RNA isolated from oviducts obtained from estradiol-treated baboons. The library was screened with a polyclonal antibody prepared against the acidic component (pl 4.5) of the glycoprotein. A single positive plaque was purified. Digestion of the recombinant plasmid with EcoRI revealed fragments of 230 and 1000 basepairs. The antibody used to screen the library was epitope selected against the fusion protein produced by the purified recombinant phage. The epitope-selected antibody, when incubated with Western blots of oviductal explant culture medium obtained from estradiol-treated baboons, recognized both the acidic and the basic variants of the glycoprotein. Northern blot hybridization with a 32P-labeled insert indicated that a single message of 2.8 kilobases was present in oviducts obtained from estradiol-treated baboons; no hybridization was detectable to RNA from oviducts obtained from progesterone-treated baboons. A mRNA of comparable size was also found in human, hamster, rabbit, and mouse oviduct tissue. In vitro translation of oviductal poly(A)+ RNA from an estradiol-treated baboon followed by immunoprecipitation with the polyclonal antibody against the acidic component indicated that the protein component of the oviductal glycoprotein had a mol wt of 66,000.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and Characterization of the Acidic Lectin from Winged Bean Seeds

Winged bean acidic lectin was purified by DEAE-Sephadex A-50 and affinity chromatography on N-acetylgalactosamine-agarose gel. The purified lectin was a glycoprotein homogeneous on polyacrylamide gel electrophoresis, isoelectric focusing, and gel filtration. The molecular weight of the lectin was 52,000 by gel filtration, and SDS-polyacrylamide gel electrophoresis gave a single component of molecular weight of 27,000. Its isoelectric point was 5.5. The acidic lectin was rich in acidic amino acids, and contained 2mol of methionine but no cystine. It also agglutinated both trypsinized and untreated human erythrocytes (types A, B, AB and O), but not rabbit erythrocytes. The hemagglutination was inhibited by d-galactose and related sugars. Modification of the acidic lectin with N-bromosuccinimide caused a concomitant loss of the hemagglutinating activity with oxidation of tryptophan residue. The acidic lectin was immunologically different from the purified winged bean basic lectin by double immunodiffusion using antiserum raised against the basic lectin.     

Biochemical properties of glycoproteins involved in lymphocyte recognition of high endothelial venules in man

Lymphocyte interactions with high endothelial venules (HEV) are important to the in vivo migration of normal and neoplastic lymphocyte populations. We have previously described an 85- to 95-kDa lymphocyte surface glycoprotein(s) defined by mAb Hermes-1, that is involved in the recognition of HEV by human lymphocytes: antibodies against distinct epitopes of the Hermes-1 Ag differentially inhibit lymphocyte binding to lymph node, mucosal, or synovial HEV. Here we characterize further the Hermes-1-defined glycoproteins. No well defined differences were observed between the Hermes-1 Ag immunoprecipitated from PBL and from mucosa- vs lymph HEV-specific cell lines. The Ag is an acidic (isoelectric point = 4.2) sulfated molecule bearing both O-linked and (3,4) N-linked oligosaccharide side chains. A subset of the Hermes-1-immunoprecipitated species is modified by covalent linkage to chondroitin sulfate, yielding a Mr of approximately 180 to 200 kDa. Pulse-chase labeling reveals a major precursor of 76 kDa that appears to be processed either to the 85- to 95-kDa form or, by addition of chondroitin sulfate, to a 180- to 200-kDa form. The potential role of these structural modifications, and particularly of chondroitin sulfate, in the function of the putative adhesion molecules is discussed.