Studies on carbohydrate binding to a lectin purified from Streptomyces sp

Proteolytic Processing, Maturation, and Unique Synteny of the Streptomyces Hemagglutinin SHA

SHA is an l-rhamnose- and d-galactose-binding lectin that agglutinates human group B erythrocytes and was first purified almost 50 years ago. Although the original SHA-producing Streptomyces strain was lost, the primary structure of SHA was more recently solved by mass spectrometry of the archived protein, which matched it to a similar sequence in the Streptomyces lavendulae genome. Using genomic and protein biochemical analyses, this study aimed to identify SHA-secreting Streptomyces strains to further investigate the expression and binding activities of these putative proteins. Of 67 strains genetically related to S. lavendulae, 17 secreted pro-SHAs in culture. Seven SHA homologues were purified to homogeneity and then subjected to liquid chromatography-high-resolution multistage mass spectrometry (LC-MS/MS) and hemagglutination (HA) assays. Processing of pro-SHAs occurred during and after purification, indicating that associated proteases converted pro-SHAs into mature SHAs with molecular masses and HA activities similar to that of the archived SHA. Previously, the SHA monomer was shown to have two carbohydrate binding sites. The present study, however, found no HA activity in pro-SHAs, suggesting that pro-SHAs have only one binding site. Genetically, the SHA gene resides in conserved syntenic regions. The published genomes of 1,234 Streptomyces strains were analyzed, revealing 18 strains with SHA genes, 16 of which localized to a unique syntenic region. The SHA syntenic region consists of ∼17 open reading frames (ORFs) and is specific to S. lavendulae-related strains. Notably, a lipoprotein gene excludes SHA from the synteny in some strains, suggesting that horizontal gene transfer events during the course of evolution shaped the distribution of SHA genes. IMPORTANCE Lectins are extremely useful molecules for the study of glycans and carbohydrates. Here, we show that homologous genes encoding the l-rhamnose- and d-galactose-binding lectins, SHAs, are present in multiple bacterial strains, genetically related to Streptomyces lavendulae. SHA genes are expressed as precursor pro-SHA proteins that are truncated and mature into fully active lectins with two carbohydrate binding sites, which exhibit hemagglutination activity for type B red blood cells. The SHA gene is located within a conserved syntenic region, hinting at specific but yet-to-be-discovered biological roles of this carbohydrate-binding protein for its soil-dwelling microbial producer.

Solvent Perturbation of Protein Structures - A Review Study with Lectins

Use of organic molecules as co-solvent with water, the ubiquitous biological solvent, to perturb the structure of proteins is popular in the research area of protein structure and folding. These organic co-solvents are believed to somehow mimic the environment near the cell membrane. Apart from that they induce non-native states which can be present in the protein folding pathway or those states also may be representative of the off pathway structures leading to amyloid formation, responsible for various fatal diseases. In this review, we shall focus on organic co-solvent induced structure perturbation of various members of lectin family. Lectins are excellent model systems for protein folding study because of its wide occurrence, diverse structure and versatile biological functions. Lectins were mainly perturbed by two fluoroalcohols - 2,2,2- trifluoroethanol and 1,1,1,3,3,3-hexafluoroisopropanol whereas glycerol, ethylene glycol and polyethylene glycols were used in some cases. Overall, all native lectins were denatured by alcohols and most of the denatured lectins have predominant helical secondary structure. But characterization of the helical states and the transition pathway for various lectins revealed diverse result.

Mass spectrometric revival of an l-rhamnose- and d-galactose-specific lectin from a lost strain of Streptomyces

Blood type B-specific Streptomyces sp. 27S5 hemagglutinin (SHA) was discovered and characterized in the 1970s. Although strain 27S5 has been lost, the purified SHA protein survived intact under frozen conditions and retained its activity. Using modern techniques, here we further characterized SHA. Fourier-transform ion cyclotron resonance MS analysis determined the average molecular mass of SHA as 13,314.67 Da. MS of digested SHA peptides, Streptomyces genomic database matching, and N-terminal sequencing solved the 131-residue amino acid sequence of SHA. We found that SHA is homologous to N-terminally truncated hypothetical proteins encoded by the genomes of Streptomyces lavendulae, Streptomyces sp. Mg1, and others. The gene of the closest homologue in S. lavendulae, a putative polysaccharide deacetylase (PDSL), encodes 68 additional N-terminal amino acids, and its C terminus perfectly matched the SHA sequence, except for a single Ala-to-Glu amino acid difference. We expressed recombinant SHA(PDSL-A108E) (rSHA) as an enzymatically cleavable fusion protein in Escherichia coli, and glycan microarray analyses indicated that refolded rSHA exhibits the blood type B- and l-rhamnose-specific characteristics of authentic SHA, confirming that rSHA is essentially identical with SHA produced by Streptomyces sp. 27S5. We noted that SHA comprises three similar domains, representing 70% of the protein, and that these SHA domains partially overlap with annotated clostridial hydrophobic with conserved W domains. Furthermore, examination of GFP-tagged SHA revealed binding to microbial surfaces. rSHA may be useful both for studying the role of SHA/clostridial hydrophobic with conserved W domains in carbohydrate binding and for developing novel diagnostics and therapeutics for l-rhamnose-containing microorganisms.

Purification and characterization of lectin from fruiting body of Ganoderma lucidum

A novel 114 kDa hexameric lectin was purified from the fruiting bodies of the mushroom Ganoderma lucidum. Biochemical characterization revealed it to be a glycoprotein having 9.3% neutral sugar and it showed hemagglutinating activity on pronase treated human erythrocytes. The lectin was stable in the pH range of 5-9 and temperature up to 50 degrees C. The hemagglutinating activity was inhibited by glycoproteins that possessed N-as well as O-linked glycans. Chemical modification of the G. lucidum lectin revealed contribution of tryptophan and lysine to binding activity. The thermodynamics of binding of bi- and triantennary N-glycans to G. lucidum lectin was studied by spectrofluorimetry. The lectin showed very high affinity for asialo N-linked triantennary glycan and a preference for asialo glycans over sialylated glycans. The binding was accompanied with a large negative change in enthalpy as well as entropy, indicating primarily involvement of polar hydrogen, van der Waals and hydrophobic interactions in the binding.

Identification of group B streptococcal antigen with lectin-bound polystyrene particles

The lectin of the tomato, Lycopersicon esculentum, or of the potato, Solanum tuberosum, can be passively coupled to amide-modified polystyrene spheres to be used as a detection reagent for the specific identification of group B streptococcal cultures grown in selective or nonselective Todd-Hewitt broth for 5 and 4 h, respectively. Agglutination occurred when the lectin reagents were allowed to react with either the cell suspension, clarified broth, or antigen extracts from group B streptococci grown in Todd-Hewitt broth. No agglutination occurred when these lectins were allowed to react with strains of serogroup A, C, D, F, or G streptococci. False-negative agglutination responses may occur with certain serotype of group B streptococci grown on Columbia sheep blood agar. A 20-min staining time permitted the specific labeling of fixed smears of group B streptococci with fluorescein-conjugated Lycopersicon lectin. The lectin from the solanaceous plant Datura stramonium did not agglutinate group B streptococci or other clinically significant streptococcal serogroups.

Characterization of the group-specific polysaccharide of group B Streptococcus

The group-specific polysaccharide of the group B Streptococcus was isolated by nitrous acid extraction followed by gel filtration on Sepharose 6B and chromatography on DEAE-Bio-Gel A. It was composed of rhamnose, galactose, N-acetylglucosamine, and glucitol phosphate. Mild periodate oxidation of the polysaccharide resulted in a rapid reduction in molecular weight, indicating that the glucitol was located in the backbone of the polymer. High-resolution 31P NMR showed the presence of a single type of phosphodiester bond in the molecule. Methylation analysis and several specific chemical degradations were done to determine sugar linkages. The basic structure of the group B polysaccharide consists of a backbone of 2-linked rhamnose, 2,4-linked rhamnose, and glucitol phosphate, and side chains of rhamnose(1----3)galactose(1----3)N-acetylglucosamine linked to the 4-position of a rhamnose in the backbone.