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

CAVADA BS; IGLESIAS MM; TRONCOSO MF; TEIXEIRA EH; TURYN D; DOMINICI FP

HORMONE AND METABOLIC RESEARCH

GEORG THIEME VERLAG KG

Año: 2003 vol. 35 p. 125 - 127

0018-5043

The insulin receptor (IR) is a heterotetrameric glycoprotein consisting of two extracellular 130 kDa a-subunits containing insulin-binding sites and two 95 kDa b-subunits having tyrosine kinase activity in their intracellular domains. Ligand binding results in the autophosphorylation of tyrosine residues in several regions of the intracellular b-subunit and the activation of the IR kinase activity towards intracellular substrates. Activation of the IR tyrosine kinase plays a key role in mediating the biological effects of insulin. Indeed, several substances that can mimic many actions of insulin are capable of activating the IR kinase. Concanavalin A (ConA), the lectin from Canavalia ensiformis (Jack bean) seeds 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 b-subunit both in a cell-free system and in intact hepatoma cells without inhibition of insulin binding. We have recently isolated lectins from beans of the plants Canavalia brasiliensis, Dioclea virgata, Dioclea rostrata, and Cratylia floribunda that belong to the same subtribe than ConA and show a very high degree of sequence conservation with this protein. Interestingly, these lectins are able to induce the same biological effects that ConA, such as stimulation of lymphocyte proliferation and stimulation of histamine release by rat peritoneal mast cells, but they differ in potency and efficiency. The present study was performed to investigate the potential insulin-like effect of the lectins from Canavalia brasiliensis, Dioclea virgata, Dioclea rostrata, and Cratylia floribunda. To that end we have analyzed their effect on the autophosphorylation of the IR purified from rat liver membranes in comparison to ConA and insulin.