Thermodynamic and kinetic analysis of porphyrin binding to Trichosanthes cucumerina seed lectin

Abstract

The interaction of several metallo-porphyrins with the galactose-specific lectin from Trichosanthes cucumeirna (TCSL) has been investigated. Difference absorption spectroscopy revealed that significant changes occur in the Soret band region of the porphyrins upon binding to TCSL and these changes have been monitored to obtain association constants (K a ) and stoichiometry of binding (n ). The dimeric lectin binds two porphyrin molecules and the presence of the specific saccharide lactose did not affect porphyrin binding significantly, indicating that the sugar and the porphyrin bind at different sites. The K a values obtained for the binding of different porphyrins with TCSL at 25 8C were in the range of 2 Â 10 3 25 Â 10 5 M 21 . Association constants for meso-tetra(4-sulphonatophenyl)porphyrinato copper(II) (CuTPPS), a porphyrin bearing four negative charges and meso-tetra(4-methylpyridinium)porphyrinato copper(II) (CuTMPyP), a porphyrin with four positive charges, were determined at several temperatures; from the temperature dependence of the association constants, the thermodynamic parameters change in enthalpy (DH8) and change in entropy (DS8) associated with the binding process were estimated. The thermodynamic data indicate that porphyrin binding to TCSL is driven largely by a favourable entropic contribution; the enthalpic contribution is very small, suggesting that the binding process is governed primarily by hydrophobic forces. Stopped-flow spectroscopic measurements show that binding of CuTMPyP to TCSL takes place by a single-step process and at 20 8C, the association and dissociation rate constants were 1.89 Â 10 4 M 21 : s 21 and 0.29 s 21, respectively.

Rapid affinity-purification and physicochemical characterization of pumpkin (Cucurbita maxima) phloem exudate lectin

“…In order to characterize the cucurbit seed lectins in greater detail, we initiated a long-term programme in the mid-1990s and reported on the purification, physicochemical characterization and carbohydrate-binding specificity of three new lectins from the seeds of Cucurbitaceae species, namely SGSL [Trichosanthes anguina (snake gourd) seed lectin], TCSL (Trichosanthes cucumerina seed lectin) and TDSL (Trichosanthes dioica seed lectin), and characterized the carbohydrate-binding properties of MCL in greater detail [12][13][14][15][16][17][18][19][20][21][22][23][24]. Additionally, the interactions of several water-soluble porphyrins with SGSL, TCSL and MCL were also investigated [25][26][27].…”

Thermodynamic analysis of porphyrin binding to Momordica charantia (bitter gourd) lectin

“…Therefore, we initiated a long‐term program to investigate the interaction of water‐soluble porphyrins with lectins. In the initial studies, we characterized the interaction of several free‐base and metalloporphyrins with plant lectins such as concanavalin A (ConA), pea lectin, jack fruit ( Artocarpus integrifolia ) agglutinin (jacalin), snake gourd ( Trichosanthes anguina ) seed lectin (SGSL) and Trichosanthes cucumerina seed lectin (TCSL) [15–18].…”

Thermodynamic studies on the interaction of water-soluble porphyrins with the glucose/mannose-specific lectin from garden pea (Pisum sativum)

“…Detailed thermodynamic analysis of porphyrin binding to two Cucurbitaceae seed lectins, namely TCSL and MCL indicated that while the TCSL-porphyrin interaction is primarily stabilized by entropic factors (18) binding of porphyrins to MCL is mediated by strong enthalpic forces, with negative contribution from entropy of binding (19). Single-crystal X-ray diffraction studies on the interaction of H 2 TSPP with different lectins, viz., Con A, jacalin and peanut agglutinin (PNA) have revealed distinctly different modes of interaction between the lectin and the porphyrin (4, 20 -22).…”