The Tryptophan Fluorescence of Tetracarbidium conophorum Agglutinin II and a Solution-Based Assay for the Binding of a Biantennary Glycopeptide
1998
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 (λex = 295 nm, λem = 350 nm) decay is complex and can be described by four decay times with the following values: τ1 = 7.4nsec, α1 = 0.22; τ2 = 2.9 nsec, α2 = 0.25; τ3 = l.0 nsec, α3 = 0.34; τ4 = 0.2 nsec, α4 = 0.18. The addition of a biantennary glycopeptide \(\begin{array}{*{20}c} {Gal\beta (1 \to 4)GlcNAc\beta (1 \to 2)Man\alpha (1 \to 6)\neg } \\ {Man\beta (1 \to 4)GlcNAC\beta (1 \to 4)GlcAc\beta (1 \to )\begin{array}{*{20}c} {Glu - Nh_2 } \\ | \\ {Asn} \\ | \\ {COOH} \\ \end{array} } \\ {Gal\beta (1 \to 4)GlcNAc\beta (1 \to 2)Man\alpha (1 \to 3)} \\ \end{array} \) 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 1.8×105 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.
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