The tryptophan fluorescence of Tetracarbidium conophorum agglutinin II and a solution-based assay for the binding of a biantennary glycopeptide.

The plant lectin Tetracarbidium conophorum agglutinin II binds to glycoproteins and glycopeptides in a structurally specific manner [Animashaun et al., (1994) Glycoconjugate J. 11, 299-303]. We have characterized the steady-state and time-resolved fluorescence of the tryptophan residues of this lectin. The fluorescence (lambda[ex] = 295 nm, lambda[em] = 350 nm) decay is complex and can be described by four decay times with the following values: tau1 = 7.4 nsec, alpha1 = 0.22; tau2 = 2.9 nsec, alpha2 = 0.25: tau3 = 1.0 nsec, alpha3 = 0.34, tau4 = 0.2 nsec, alpha4 = 0.18. The addition of a biantennary glycopeptide (carbohydrate sequence [see text]) to the lectin results in a quench and an 8 nm blue shift of the emission spectrum. The effect is saturable, and is described by an association constant of 1.8 x 10(5) M(-1). The tryptophan fluorescence of Tetracarbidium conophorum agglutinin II may therefore be utilized to characterize thermodynamically the binding interactions between this lectin and complex glycoprotein.

The complex-type oligosaccharide binding lectin Datura stramonium agglutinin detects type II A muscle fibres in the branchial biceps from man and cat.

Complex-type oligosaccharides were detected in the sarcoplasm of muscle fibres from cat and human biceps using lectins and anticarbohydrate antibodies. The lectin Datura stramonium agglutinin strongly stained type II A fibres as identified by myosin ATPase activity after alkaline and acid preincubation. In contrast, all muscle fibres showed a moderate coarse granular staining after incubation with Tetracarpidum conophorum agglutinin and Telfairia occidentalis agglutinin which recognize tri-antennary complex glycans poorly bound by D. stramonium agglutinin. Strong sarcoplasmic staining in all muscle fibres was obtained after incubation with an antibody against branched N-acetyllactosamine structure while an antibody against binary 2 --> 3 sialyllactosamine glycans failed to detect the muscle fibres. Treatment of the muscle sections with sialidase prior to incubation with D. stramonium agglutinin did not influence the lectin staining pattern. Staining of blots from electrophoretically separated muscle proteins obtained by homogenization, solubilization and centrifugation of small muscle pieces showed D. stramonium agglutinin binding to a number of bands ranging from 200 kDa to 30 kDa. No D. stramonium agglutinin positive bands were observed in blots from separated mitochondrial proteins while blots from sarcoplasmic reticulum separated by electrophoresis stained many bands in the range from 200 kDa to 30 kDa. It may be concluded that all muscle fibres in human and cat biceps hold intracellular non-sialylated complex-type oligosaccharides and further, that a specific tri-antennary complex-type glycoform is strongly expressed in type II A fibres as recognized by D. stramonium agglutinin. These results indicate a different glycosylation of certain myofibrillar-associated proteins in muscle fibre types.

Characterization of isolectins in Tetracarpidium conophorum seeds (Nigerian walnut).

A lectin preparation obtained from Tetracarpidium conophorum (Nigerian walnut) by affinity chromatography of seed extracts on lactose-agarose has been shown to contain two components by gel filtration on Sephadex G150. The larger component Tetracarpidium conophorum agglutinin I (TCAI) is a disulphide-bonded 70 kDa homodimer whereas the second component TCAII is a 34 kDa monomeric protein. Amino terminal aminoacid sequencing shows identity in TCAI and TCAII for the first fifteen residues after which the sequences diverge. The N-terminal sequences of TCAI and TCAII show identity with sequences in the B-chains of ricin and Ricinus communis agglutinin I (RCAI) in eleven of the initial fifteen residues. Thereafter TCAI appears to be homologous to the ricin B chain whereas TCAII is more homologous with the B chain of RCAI. A limited screening of the carbohydrate-binding specificity of TCAII by affinity chromatography of defined oligosaccharides on TCAII Sepharose columns shows that the binding specificity reported earlier for affinity purified Tetracarpidium conophorum isolectins (Sato S, Animashaun T, Hughes RC (1991) J Biol Chem 266:11485-94) reflects the binding properties of TCAII which is the major isolectin in unfractionated lectin preparations.

Bowringia mildbraedii agglutinin: polypeptide composition, primary structure and homologies with other legume lectins.

The amino-acid sequences of the subunits of the lectin BMA from seeds of Bowringia mildbraedii have been determined. The data indicate that the lectin consists of a precursor polypeptide of approx. 29 kDa that is cleaved almost completely into two fragments of approx. 13.3 kDa (alpha subunit) and approx. 11.9 kDa (beta subunit), respectively. The beta subunit represents the N-terminal half of precursor polypeptides and is disulphide-linked in a beta beta dimer in the native (alpha beta)2 protein. BMA shows extensive amino-acid sequence homologies with known legume lectins. The site of post-translational proteolysis of the putative precursor occurs at a position similar to that identified in lectins obtained from other Sophoreae plants such as Sophora japonica and in Diocleae lectins such as Concanavalin A, but different from that of two chain lectins obtained from other tribes of the Papilionaceae.

Interactions of Bowringia mildbraedii agglutinin with complex- and hybrid-type glycans.

Affinity chromatography on Bowringia mildbraedii agglutinin (BMA) Sepharose of glycopeptides confirmed a previous report using oligosaccharides (Animashaun, T. and Hughes, R. C. (1989) J. Biol. Chem. 264,4657-4663) that high affinity binding requires the sequence Man alpha 1---2 Man alpha 1----6 Man alpha 1----6 Man beta 1----4. However, moderate binding was still exhibited by structures lacking this sequence provided the oligosaccharide core sequence Man alpha 1----3[Man alpha 1----6]Man beta 1----4GlcNAc was present. This moderate binding was not affected by substitution with N-acetylglucosamine at C2 and C4, respectively, of the Man alpha 1----3 and Man beta 1----4 residues and BMA Sepharose should prove to be a useful tool for the isolation of bisected or non-bisected hybrid-type glycans.

Carbohydrate-binding specificity of Tetracarpidium conophorum lectin.

The carbohydrate-binding specificity of a novel plant lectin isolated from the seeds of Tetracarpidium conophorum (Nigerian walnut) has been studied by quantitative hapten inhibition assays and by determining the behavior of a number of oligosaccharides and glycopeptides on lectin-Sepharose affinity columns. The Tetracarpidium lectin shows preference for simple, unbranched oligosaccharides containing a terminal Gal beta 1----4GlNAc sequence over a Gal beta 1----3GlcNAc sequence and substitution by sialic acid or fucose of the terminal galactose residue, the subterminal N-acetylglucosamine or more distally located sugar residues of oligosaccharides reduce binding activity. Branched complex-type glycans containing either Gal beta 1----4GlcNAc or Gal beta 1----3GlcNAc termini bind with higher affinity than simpler oligosaccharides. The lectin shows highest affinity for a tri-antennary glycan carrying Gal beta 1----4GlcNAc substituents on C-2 and C-4 of Man alpha 1----3 and C-2 of Man alpha 1----6 core residues. Bi- and tri-glycans lacking this branching pattern bind more weakly. Tetra-antennary glycans and mono- and di-branched hybrid-type glycans also bind weakly to the immobilized lectin. Therefore, Tetracarpidium lectin complements the binding specificities of well-known lectins such as Datura stramonium agglutinin, Phaseolus vulgaris agglutinin, and lentil lectin and will be a useful additional tool for the identification and separation of complex-type glycans.

The occurrence of Branhamella catarrhalis and other commensal Neisseriaceae in clinical sputum specimens in Lagos, Nigeria.

Branhamella catarrhalis and other commensal Neisseria species were isolated from 200 out of 500 sputum samples from patients with lower respiratory tract (LRT) infections at the Lagos University Teaching Hospital (LUTH). B. catarrhalis was isolated from 60 (12%). The isolation rates for other Neisseria species were as follows: N. mucosa from 45 (9%), N. sicca from 40 (8%), N. lactamica from 35 (7%), N. cinerea from 12 (2.4%) and N. subflava from 8 (1.6%). B. catarrhalis occurred in pure cultures in 15 (25%) of the 60 samples positive for this organism. Twenty (33%) out of the 60 N. catarrhalis isolates were beta-lactamase positive.

Bowringia milbraedii agglutinin. Specificity of binding to early processing intermediates of asparagine-linked oligosaccharide and use as a marker of endoplasmic reticulum glycoproteins.

We have purified a protein with hemagglutinating activity from the seeds of a West African legume, Bowringia milbraedii. The purified protein, designated BMA, has a native Mr = 38,000 on gel filtration and a subunit size of Mr = 16,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing or nonreducing conditions. Hemagglutination was inhibited most effectively by Man alpha 1----2 linked sugars. Affinity chromatography of oligosaccharides on BMA-Sepharose showed that Man alpha 1----2Man alpha 1----2Man alpha 1----3Man beta 1----4GlcNAcol (where GlcNAcol is N-acetylglucosaminitol) and Man alpha 1----2Man alpha 1----3Man beta 1----4GlcNAcol were retarded on the column, whereas Man alpha 1----3Man beta 1----4GlcNAcol did not bind. Oligomannosidic-type glycans obtained by treatment of [3H] mannose-labeled baby hamster kidney cells with endo-beta-N-acetylglucosaminidase H bound more strongly to BMA-Sepharose and required 10 or 200 mM methyl-alpha-mannoside for elution. Oligosaccharides bearing the sequence Man alpha 1----2Man alpha 1----6Man alpha 1----6Man, i.e. Man9GlcNAc and certain isomers of Man8GlcNAc and Man7GlcNAc, bound more tightly than other Man8 GlcNAc and Man7GlcNAc isomers lacking this sequence. Man6GlcNAc and Man5GlcNAc were weakly bound. These results suggest that BMA binds preferentially to glycoproteins that are subjected to early steps of oligosaccharide processing in the endoplasmic reticulum but not to glycoproteins that are exposed to more extensive processing by Golgi mannosidases. Staining of permeabilized cells with BMA-chromophore conjugates revealed a reticular cytoplasmic pattern consistent with a preferential visualization of the endoplasmic reticulum. BMA staining was less evident in the juxtanuclear regions that were stained brightly with wheat germ agglutinin, a lectin that binds preferentially to sialylated glycoproteins located in Golgi compartments.