Glucose-mannose binding lectins isolated from Brazilian beans stimulate the autophosporylation of the insulin receptor in vitro

CAVADA, BENILDO; IGLESIAS, MARÍA MERCEDES; TRONCOSO, MARÍA FERNANDA; TEXEIRA, EH; TURYN, DANIEL; DOMINICI, FERNANDO

HORMONE AND METABOLIC RESEARCH

Georg Thieme Verlag Stuttgart

Lugar: Nueva York; Año: 2003 vol. 35 p. 125 - 127

0018-5043

Insulin binding results in the autophosphorylation of the insulin receptor (IR) and activation of the IR tyrosine kinase plays a key role in mediating the biological effects of insulin. Concanavalin A (ConA) binds to cell surface glycoproteins with a high specificity for gluco- and manno-pyranosides and has been shown to stimulate the phosphorylation of the IR. In this study, lectins isolated from seeds of plants belonging to the Dioclinae subtribe, Canavalia brasiliensis (ConBr), Dioclea virgata (Dv), Dioclea rostrata (Dr) y Cratylia floribunda (Cf), were able to stimulate the autophosphorylation of purified IRs in a dose-dependent manner. This  result is striking, considering their high amino acid sequence homology with ConA and identical specificity, Incubation with ConA (40 mg/ml) stimulated the autophosphorylation of purified IRs in 84 ± 12 %, ConBr and Dr lectins increased the autophosphorylation in 93 ± 18 and 92 ± 8 % respectively at concentrations of 4 mg/ml. Dv and Cf showed less potency and eficay, stimulating the autophosporylation in 48 ± 15 and 58 ± 11 % respectively at the higher concentration (400 mg/ml). Under the same conditions, incubation with insulin resulted in 5- to 7- fold stimulation of the IR phosphorylation. Neither Con-A nor any of the lectins investigated produced systematic inhibition of 125I insulin binding to purified Irs even when added to concentrations as high as 400 mg/ml. This finding suggests that these proteins may mimic the actions of insulin and thus be potentially useful as antidiabetic agents