Purification and characterization of a sialic acid specific lectin from the hemolymph of the freshwater crab Paratelphusa jacquemontii

Isolation and characterization of a lectin-like chitinase from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii

A lectin was isolated from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii by affinity chromatography using mucin-sepharose matrix. The purity of the isolated lectin was confirmed in native gradient PAGE that showed a single protein band of ∼37.9 kDa. In SDS-PAGE also one band of ∼43.3 kDa molecular weight was observed that indicated the protein to be a monomer. The band from the SDS-PAGE gel was identified through mass spectrometry as chitinase 1. The purified chitinase (50 μg/ml) hemagglutinated rabbit RBCs and, mucin and glucose inhibited hemagglutination with minimum concentrations of 0.1 mg/ml and 100 mM, respectively. Bacterial agglutination with Gram -ve Vibrio harveyi, Aeromonas sobria and Escherichia coli was also observed by this protein. Thus, chitinase 1 showed lectin-like properties besides its chitin hydrolytic activity. In western blot with hepatopancreas sample, rabbit antiserum against chitinase 1 cross-reacted to two additional proteins namely, chitinase 1C and obstructor E (a chitin-binding protein, CBP), besides its specific reactivity. An indirect ELISA was developed with the antiserum to quantify chitinases/CBP in hepatopancreas and serum samples of M. rosenbergii. The assay was used in samples from juvenile prawns following V. harveyi challenge. At 72 h post-challenge, significantly higher levels of chitinases/CBP were quantified in the hepatopancreas of the challenged group (1.8 ± 0.2 mg/g tissue) compared to the control (1.2 ± 0.1 mg/g tissue). This study suggests that the chitinase 1 protein with lectin-like properties is possibly induced at the protein level and can be putatively involved in the innate immune response of M. rosenbergii.

Antimicrobial, anti-inflammatory and anti-arthritic activity of hemolymph lectin (NagLec) isolated from the freshwater crab, Oziotelphusanaga

Lectins are non-immune glycoproteins or proteins having a unique capacity to interact with carbohydrate ligands found on the surface of their host cells. In the present investigation, the lectin was purified from the hemolymph of freshwater crab, Oziotelphusa naga and its antimicrobial, anti-inflammatory and anti-arthritic activity was analysed. The preliminary characterization of the hemagglutinin was carried out to identify the erythrocyte and sugar specificity, optimum pH and temperature and cation dependency. The agglutinin was found to be highly specific to rabbit erythrocyte and inhibited by fetuin and α-lactose. Maximum hemagglutination activity was noted at pH 7.5-8 and temperature 20-40 °C. An O-acetyl sialic acid specific 75 kDa hemolymph lectin, designated as NagLec was isolated from the freshwater crab, Oziotelphusa naga by affinity chromatography on fetuin coupled Sepharose 4 B, with a purification fold of 185. The bacteria Staphylococcus aureus, Proteus mirabilis and fungus Candida albicans had the greatest zone of inhibition when treated with NagLec. The results of the Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) assays showed that the purified lectin inhibited the growth of Staphylococcus aureus at 0.031 and 0.065 μg/ml, which proved the bactericidal property of NagLec. NagLec generated alterations on the bacterial cells and led to protein leakage, which was dosage (24 and 48 μg/ml) and time dependent (10-40 min). COX and LOX enzyme was inhibited to 49.43% and 61.81% with 100 μg/ml concentration of NagLec respectively, demonstrating NagLec's ability to reduce inflammation. Furthermore, NagLec (500 μg) suppressed protein denaturation up to 77.12% whereas diclofenac sodium (a standard drug) was inhibited by 89.36%. The results indicate that NagLec, a sialic acid specific lectin isolated from the freshwater crab O. naga could be formulated as a nano drug in future owing to its antimicrobial, anti-inflammatory and anti-arthritic potential that could be targeted to specific pathogenic microbes and treat arthritis.

Characterization of a novel O-acetyl sialic acid specific lectin from the hemolymph of the marine crab, Atergatis integerrimus (Lamarck, 1818)

An O-acetyl sialic acid specific lectin was purified from the hemolymph of the marine crab Atergatis integerrimus by affinity chromatography using BSM (Bovine Submaxillary Mucin) coupled to cyanogen bromide activated Sepharose 4B and biospecific adsorption using formalinized buffalo erythrocytes. The purified AiL (Atergatis integerrimus lectin) showed an 1218 fold increase in specific activity when compared to the crude hemolymph agglutinin. The lectin, on non - denaturing PAGE showed a single band of 216 kDa and when subjected to SDS - PAGE, the lectin resolved into three subunits of molecular weight 70, 72 and 74 kDa. Physico chemical characterization revealed the lectin as pH and temperature sensitive, calcium dependent and sensitive to calcium chelators. Based on the calcium dependency of the lectin, AiL could be classified as a C-type lectin. The purified lectin agglutinated buffalo erythrocytes with greater avidity and was inhibited by the glycoproteins BSM, thyroglobulin, fetuin, PSM, and sugars raffinose, trehalose, l - fucose, α - Lactose, melibiose and GluNAc suggesting the affinity of the lectin to sialic acid. Reduction in HA with asialo buffalo erythrocytes and HAI titer with desialylated BSM, confirms the sialic acid specificity of the lectin. The reduction in HAI following de - O - acetylation confirms the specificity of the lectin for O - acetyl sialic acid. FTIR analysis confirms the purified lectin as a glycoprotein with spectral bands corresponding to amide bands and saccharides. Thus this study paves way to assess the therapeutic application of this lectin that could be targeted to modified sialic acid moieties that are expressed on the malignant cells and pathogenic microbes and also deduce the crystal structure of the lectin.

Immune response of anti-lectin Pjlec antibody in freshwater crab Paratelphusa jacquemontii

Sialic acid specific lectin Pjlec isolated from serum of the freshwater crab Paratelphusa jacquemontii served as an antigen for the production of immunoglobulin (Ig) in Balb/c mice sera. Enzyme-linked immunosorbent assay (ELISA) of mice anti-sera with Pjlec lectin affirmed the induction and production of antibody. Anti-Pjlec antibody was isolated from the antisera of mice by Protein A Sepharose affinity chromatography and checked for purity by immunoblot with lectin. Mass spectrometry (MS/MS) of papain digethe peptide sequence of antigen binding fragment (Fab) and fragment crystallizable (Fc). Coatingsted anti-Pjlec revealed of anti-Pjlec to the target cell, rabbit erythrocyte failed to enhance in vitro phagocytosis in the crab. However, inoculation of anti-Pjlec in the hemolymph of the crab elicited in vitro phagocytosis. Proteins in hemocyte lysate supernatant (HLS) were separated by electrophoresis failed to immunoblot with Pjlec or anti-Pjlec. Peptide sequences of trypsin digested lectin protein appeared homologous to deuterostome chordate. The protostome crab that lack the ability to synthesize sialic acid however bind to sialic acid a deuterostome sugar to suggest the complexity in innate immune system of invertebrates. The application of lectin and its antibody require further study on application of pathological conditions associated with alterations in sialylated cell surface.

Purification, characterization and functional analysis of the immune molecule lectin from the haemolymph of blue swimmer crab Portunus pelagicus and their antibiofilm properties

The present study reveals purification and characterization of immune molecule lectin from the haemolymph of blue swimmer crab Portunus pelagicus (Pp-Lec). The Pp-Lec was purified by affinity chromatography with mannose coupled sepharose CL-4B column and it exhibits single band with a molecular weight of 155 kDa in SDS-PAGE. The surface morphology of purified Pp-Lec displays the homogeneous nature of protein. A distinct peak with a retention time of 3.3 min was appeared in high performance liquid chromatography (HPLC) and X-ray diffraction (XRD) analysis expresses a single peak at 31.5° which shows the purity and crystalline nature of the protein respectively. Functional analysis of purified Pp-Lec exhibits encapsulation activity against sepharose beads and yeast agglutination activity against Saccharomyces cerevisiae. Moreover, the purified Pp-Lec has the ability to agglutinates with the human erythrocytes among tested and which was observed by light microscopy. In addition, purified Pp-Lec showed the broad spectrum of antibacterial activity against Gram-positive Bacillus pumulis, Bacillus thuringiensis, Enterococcus faecalis and Gram negative Citrobacter amalonaticus, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Proteus vulgaris, Citrobacter murliniae, Citrobacter freundii, Morganella morganii. Antibiofilm potential of purified Pp-Lec against selective Gram-negative bacteria showed the disruption of biofilm architecture at the concentration of 50 μg ml^-1.

Lectin activity in mycelial extracts of Fusarium species

Lectins are non-immunogenic carbohydrate-recognizing proteins that bind to glycoproteins, glycolipids, or polysaccharides with high affinity and exhibit remarkable ability to agglutinate erythrocytes and other cells. In the present study, ten Fusarium species previously not explored for lectins were screened for the presence of lectin activity. Mycelial extracts of F. fujikuroi, F. beomiformii, F. begoniae, F. nisikadoi, F. anthophilum, F. incarnatum, and F. tabacinum manifested agglutination of rabbit erythrocytes. Neuraminidase treatment of rabbit erythrocytes increased lectin titers of F. nisikadoi and F. tabacinum extracts, whereas the protease treatment resulted in a significant decline in agglutination by most of the lectins. Results of hapten inhibition studies demonstrated unique carbohydrate specificity of Fusarium lectins toward O-acetyl sialic acids. Activity of the majority of Fusarium lectins exhibited binding affinity to d-ribose, l-fucose, d-glucose, l-arabinose, d-mannitol, d-galactosamine hydrochloride, d-galacturonic acid, N-acetyl-d-galactosamine, N-acetyl-neuraminic acid, 2-deoxy-d-ribose, fetuin, asialofetuin, and bovine submaxillary mucin. Melibiose and N-glycolyl neuraminic acid did not inhibit the activity of any of the Fusarium lectins. Mycelial extracts of F. begoniae, F. nisikadoi, F. anthophilum, and F. incarnatum interacted with most of the carbohydrates tested. F. fujikuroi and F. anthophilum extracts displayed strong interaction with starch. The expression of lectin activity as a function of culture age was investigated. Most species displayed lectin activity on the 7th day of cultivation, and it varied with progressing of culture age.

Opsonic function of sialic acid specific lectin in freshwater crab Paratelphusa jacquemontii

The sialic acid specific humoral lectin, Pjlec of the freshwater crab Paratelphusa jacquemontii was investigated for its opsonin function with rabbit erythrocyte as target cell for phagocytosis by the crab's hemocyte. The untreated or trypsin treated erythrocyte induced lectin response after challenge however failed when treated with neuraminidase evidently indicating glycan dependency for elicited immune response. Our observation of in vitro phagocytosis of the erythrocyte untreated or coated with serum, clarified serum appeared to be recognized and engulfed by hemocytes but when coated with isolated lectin Pjlec, the response was elicited. Moreover, with trypsin treated erythrocyte the response remained unchanged but neuraminidase or O-glycosidase treatment eliminated the response reaction. This suggested the sialic acid specific reaction of lectin with the erythrocyte and was essential for recognition to allow the lectin Pjlec to act as an opsonin. The flowcytometry observation affirmed the enhancement of phagocytosis by Pjlec coated hemocyte. The efficiency of in vitro hemolysis of Pjlec coated erythrocyte with hemocyte when compared to untreated erythrocyte with or without hemocyte also established the opsonic function of the lectin. The mechanism of phagocytosis and induction were dependent on specific recognition of the erythrocyte by the multivalent binding site of the lectin protein, and the elicitation of the immune response was a function of the sialoglycan surface. The pathway of the challenge suggested that after entry of nonself recognition by lectin was followed by induction and activation of phagocytosis by opsonic binding of the lectin.

Characterization of a lectin from the craysfish Cherax quadricarinatus hemolymph and its effect on hemocytes

Lectins participate in the immune mechanisms of crustaceans. They have been considered as humoral receptors for pathogen-associated molecular patterns; however, some reports suggest that lectins could regulate crustacean cellular functions. In the present study, we purified and characterized a serum lectin (CqL) from the hemolymph of Cherax quadricarinatus by affinity chromatography and determined its participation in the regulation of hemocytes' oxidative burst. CqL is a 290-kDa lectin in native form, constituted by 108, 80, and 29-kDa subunits. It is mainly composed of glycine, alanine, and a minor proportion of methionine and histidine. It showed no carbohydrates in its structure. CqL is composed of several isoforms, as determined by 2D-electrophoresis, and shows no homology with any crustacean protein as determined by Lc/Ms mass spectrometry. CqL agglutinated mainly rat and rabbit erythrocytes and showed a broad specificity for monosaccharides such as galactose, glucose, and sialic acid, as well as for glycoproteins, such as porcine stomach and bovine submaxillary mucin and fetuin. It is a Mn(2+)-dependent lectin. CqL recognized 8% of crayfish granular hemocytes and increased 4.2-fold the production of hemocytes' superoxide anion in vitro assays when compared with non-treated hemocytes. This effect showed the same specificity for carbohydrates as hemagglutination; moreover, superoxide dismutase and diphenyleneiodonium chloride were effective inhibitors of CqL oxidative-activation. The CqL homoreceptor is a 120-kDa glycoprotein identified in the hemocytes lysate. Our results suggest that CqL participates actively in the regulation of the generation of superoxide anions in hemocytes using NADPH-dependent mechanisms.

Identification and analysis of o-acetylated sialoglycoproteins

5-N-acetylneuraminic acid, commonly known as sialic acid (Sia), constitutes a family of N- and O-substituted 9-carbon monosaccharides. Frequent modification of O-acetylations at positions C-7, C-8, or C-9 of Sias generates a family of O-acetylated sialic acid (O-AcSia) and plays crucial roles in many cellular events like cell-cell adhesion, proliferation, migration, etc. Therefore, identification and analysis of O-acetylated sialoglycoproteins (O-AcSGPs) are important. In this chapter, we describe several approaches for successful identification of O-AcSGPs. We broadly divide them into two categories, i.e., invasive and noninvasive methods. Several O-AcSias-binding probes are used for this purpose. Detailed methodologies for step-by-step identification using these probes have been discussed. We have also included a few invasive analytical methods for identification and quantitation of O-AcSias. Several indirect methods are also elaborated for such purpose, in which O-acetyl group from sialic acids is initially removed followed by detection of Sias by several approaches. For molecular identification, we have described methods for affinity purification of O-AcSGPs using an O-AcSias-binding lectin as an affinity matrix followed by sequencing using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF-TOF) mass spectroscopy (MS). In spite of special attention, loss of O-acetyl groups due to its sensitivity towards alkaline pH and high temperature along with migration of labile O-acetyl groups from C7-C8-C9 during sample preparation is difficult to avoid. Therefore there is always a risk for underestimation of O-AcSias.

Review: Immunity mechanisms in crustaceans

Crustacean aquaculture represents a major industry in tropical developing countries. As a result of high culture densities and increasing extension of aquaculture farms, the presence of diseases has also increased, inducing economic losses. Invertebrates, which lack adaptive immune systems, have developed defense systems that respond against antigens on the surface of potential pathogens. The defense mechanisms of crustaceans depend completely on the innate immune system that is activated when pathogen-associated molecular patterns are recognized by soluble or by cell surface host proteins, such as lectins, antimicrobial, clotting, and pattern recognition proteins, which, in turn, activate cellular or humoral effector mechanisms to destroy invading pathogens. This work is aimed at presenting the main characteristics of the crustacean proteins that participate in immune defense by specific recognition of carbohydrate containing molecules, i.e. glycans, glycolipids, glycoproteins, peptidoglycans, or lipopolysaccharides from Gram-negative and Gram-positive bacteria, viruses, or fungi. We review some basic aspects of crustacean effector defense processes, like agglutination, encapsulation, phagocytosis, clottable proteins, and bactericidal activity, induced by these carbohydrate-driven recognition patterns.

Evaluation of non-specific immune components from the skin mucus of olive flounder (Paralichthys olivaceus)

The innate immune system, particularly the external body surface, plays a frontier role in protecting fish under intensive aquaculture and at prolonged low temperatures from relevant infections due to inadequate adaptive immune responses. In the present study we aimed to understand the mucosal immunity of an economically important mariculture fish, olive flounder (Paralichthys olivaceus) by evaluating the immune components from its skin mucus. The activities of lysozyme (233.33+/-171.82 units mg(-1)), trypsin-like protease (42.84+/-1.249 units mg(-1)), alkaline phosphatase (0.376+/-0.005 units mg(-1)) and esterase (0.170+/-0.006 units mg(-1)) were detected in the skin mucus. Transferrin was identified by MALDI-TOF/MS analysis. ELISA and immunoblot assays using anti-flounder IgM monoclonal antibody showed the presence of a significant level (1.80+/-0.001, n=3) of monomer immunoglobulin M (IgM) with approximate molecular weight of 160 and 25 kDa under non-denaturing and denaturing states, respectively. Skin mucus showed strong antibacterial activity against tested fish pathogenic bacteria. In addition, skin mucus successfully agglutinated (HA titre 2(8)), but completely failed to haemolyse, rabbit erythrocytes. In conclusion, the major immune components of the skin mucus, identified in the present study, are possibly involved in the broad spectrum non-specific immunity of olive flounder.

A novel C-type lectin from abalone, Haliotis discus discus, agglutinates Vibrio alginolyticus

Owing to its specific binding to carbohydrates, lectins play important roles in pathogen recognition and clearance in invertebrate animals. In this study, a novel C-type lectin (designated CLHd) gene was isolated from abalone, Haliotis discus discus, cDNA library. The complete cDNA sequence of the CLHd gene is 508 base pairs in length, and encodes 151 amino acids. CLHd shares a highly conserved carbohydrate recognition domain with C-type lectins from mollusk and fish. The mRNA expressions of CLHd in healthy and bacterial-challenged abalones were examined using semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). CLHd mRNA transcription was up-regulated by Vibrio alginolyticus challenge and reached the maximum expression at 24h after the bacterial injection. To understand its biological activity, the recombinant CLHd gene was constructed and expressed in Escherichia coli. The recombinant CLHd specifically agglutinated V. alginolyticus at a concentration of 50microg/ml in a calcium-dependant way. Both the gene expression analysis and recombinant protein activity assay suggest that CLHd is an important immune gene involved in the recognition and elimination of pathogens in abalones.

Purification and characterisation of a natural lectin from the serum of the shrimp Litopenaeus vannamei

A natural lectin from the serum of the shrimp Litopenaeus vannamei was purified to homogeneity by a single-step affinity chromatography using fetuin-coupled agarose. The purified serum lectin (named LVL) showed a strong affinity for human A/B/O erythrocytes (RBC), mouse RBC, chicken RBC and its haemagglutinating (HA) activity was specifically dependent on Ca2+ and reversibly sensitive to EDTA. LVL inactive form had a molecular mass estimate of 172 kDa and was composed of two non-identical subunits (32 and 38 kDa) cross-linked by interchain disulphide bonds. Significant LVL activity was observed between pH 7 and 11. In HA-inhibition assays performed with several carbohydrates and glycoproteins, LVL showed a distinct and unique specificity for GalNAc/GluNAc/NeuAc which had an acetyl group, while glycoproteins fetuin and bovine submaxillary mucin (BSM) had sialic acid. Moreover, this agglutinin appeared to recognise the terminal N- and O-acetyl groups in the oligosaccharide chain of glycoconjugates. The HA activity of L. vannamei lectin was also susceptible to inhibition by lipopolysaccharides from diverse Gram-negative bacteria, which might indicate a significant in vivo role of this humoral agglutinin in the host immune response against bacterial infections.

A mushroom lectin from ascomycete Cordyceps militaris

A mushroom lectin has been purified from ascomycete Cordyceps militaris, which is one of the most popular mushrooms in eastern Asia used as a nutraceutical and in traditional Chinese medicine. This lectin, designated CML, exhibited hemagglutination activity in mouse and rat erythrocytes, but not in human ABO erythrocytes. SDS-PAGE of CML revealed a single band with a molecular mass of 31.0 kDa under both nonreducing and reducing conditions that was stained by silver nitrate, and a 31.4 kDa peak in a Superdex-200 HR gel-filtration column. The hemagglutination activity was inhibited by sialoglycoproteins, but not in by mono- or disaccharides, asialoglycoproteins, or de-O-acetylated glycoprotein. The activity was maximal at pH 6.0-9.1 and at temperatures below 50 degrees C. Circular dichroism spectrum analysis revealed that CML comprises 27% alpha-helix, 12% beta-sheets, 29% beta-turns, and 32% random coils. Its binding specificity and secondary structure are similar to those of a fungal lectin from Arthrobotrys oligospora. However, the N-terminal amino acid sequence of CML differs greatly from those of other lectins. CML exhibits mitogenic activity against mouse splenocytes.

Affinity Proteomic Approach for Identification of an IgA-like Protein in Litopenaeus vannamei and Study on Its Agglutination Characterization

An unknown protein reacted with anti-human IgA, namely, IgA-like protein, has been reported in shrimp, but information regarding its identification is not available. In the present study, an affinity proteomic strategy was applied to identify the IgA-like protein of shrimp Litopenaeus vannamei. The protein of 75 kDa was isolated and confirmed by affinity chromatography and Western blotting with goat anti-human IgA, respectively, and then identified as hemocyanin, a member of IgSF, by mass spectrometry. Moreover, our results showed that human IgA and L. vannamei hemocyanin could separately react with goat anti-human IgA or rabbit anti-shrimp affinity hemocyanin (a-hemocyanin). Further evidences indicated that the recombinant protein of the Ig-like conserved domain could react with anti-human IgA. Interestingly, our results indicated that L. vannamei hemocyanin could aggregate with eight species of shrimp pathogenic bacteria and four types of animal erythrocytes directly. These results indicate that L. vannamei hemocyanin, an IgA-like protein, has dual function of reaction with anti-human IgA as an antigen and of activity binding to bacteria and animal erythrocytes as an agglutinin, suggesting its characteristic role as an IgSF molecule. In addition, our approach suggests that affinity proteomics based on heterogeneous antibody can speed up the identification of Fossman antigens.

Purification, characterization and cDNA cloning of a novel lipopolysaccharide-binding lectin from the shrimp Penaeus monodon

In invertebrates, C-type lectin plays an important role in innate immunity by mediating the recognition of pathogens to host cells and clearing microinvaders. A few C-type lectins have been identified from shrimps, but none of their gene or protein sequences is known to date. In this paper, a C-type lectin (named PmLec) specific for bacterial lipopolysaccharide was purified from the serum of the shrimp Penaeus monodon. The binding of PmLec to lipopolysaccharide was mainly mediated through the O-antigen. PmLec had a strong hemagglutinating and bacterial-agglutinating activity as well as an opsonic effect that enhances hemocyte phagocytosis. The PmLec cDNA sequence was obtained from the cDNA library of P. monodon by polymerase chain reaction with the degenerated primer designed according to the amino-terminal residue sequence of purified PmLec. A 546-bp open reading frame was found to encode a putative protein comprising 182 amino acids and containing a preceding signal peptide of 17 amino acids. A C-type lectin domain existed in PmLec, but no glycosylation site was found. The recombinant PmLec protein expressed in Escherichia coli also showed the same agglutinating activity and opsonic effect as that of the native protein. This is the first report of a lectin cDNA from the shrimp. PmLec functions as a pattern-recognition protein and an opsonin in the shrimp, and it provides a clue to elucidate the role of lectin in the innate immunity of aquatic invertebrates at the molecular level.

The Streptococcus gordonii surface proteins GspB and Hsa mediate binding to sialylated carbohydrate epitopes on the platelet membrane glycoprotein Ibalpha

Platelet binding by Streptococcus gordonii strain M99 is dependent on expression of the cell wall-anchored glycoprotein GspB. This large cell surface protein is exported from the M99 cytoplasm via a dedicated transport system that includes SecA2 and SecY2. GspB is highly similar to Hsa, a protein expressed by S. gordonii Challis that has been characterized as a sialic acid binding hemagglutinin. In this study, we compared the contribution of GspB and Hsa to the adherence of S. gordonii to selected glycoproteins. Our results indicate that GspB can mediate binding to a variety of sialylated glycoproteins. GspB facilitates binding to carbohydrates bearing sialic acid in either alpha(2-3) or alpha(2-6) linkages, with a slight preference for alpha(2-3) linkages. Furthermore, GspB readily mediates binding to sialic acid residues on immobilized glycocalicin, the extracellular portion of the platelet membrane glycoprotein (GP) Ibalpha (the ligand binding subunit of the platelet von Willebrand factor receptor complex GPIb-IX-V). Although Hsa is required for the binding of S. gordonii Challis to sialic acid, most of the Hsa expressed by Challis is retained in the cytoplasm. The deficiency in export is due, at least in part, to a nonsense mutation in secA2. Hsa export can be enhanced by complementation with secA2 from M99, which also results in significantly greater binding to sialylated glycoproteins, including glycocalicin. The combined results indicate that GspB and Hsa contribute similar binding capabilities to M99 and Challis, respectively, but there may be subtle differences in the preferred epitopes to which these adhesins bind.