PLANT UREASES: A NOVEL GROUP OF MULTIFUNCTIONAL PROTEINS WITH INSECTICIDAL PROPERTIES

CARLINI, C.R.(1), FOLLMER, C. (1), PIRES-ALVES, M. (1), FERREIRA DA SILVA, C.T. (1),

(1)Departamento de.Biofísica, IB, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91.501-907.

Plants produce a wide array of substances including proteins, such as lectins, chitinases, enzyme inhibitors, ribosome-inactivating proteins, etc, in response to a multitude of predators and pathogens. Canatoxin (CNTX)-like proteins and urease constitute a novel group of multifunctional proteins with a putative role in plant defense against insect predation and phytopathogenic fungi. CNTX is a neurotoxic protein (184 kDa) from jackbeans (Canavalia ensiformis), lethal to mice and rats by intraperitoneal route, but inactive if given orally. CNTX is also lethal when ingested by a group of insects with cathepsin-based digestion, in which the protein is proteolitically “activated” to give a 10 kDa entomotoxic peptide. Determination of partial aminoacid sequence indicated a high homology with urease found in the same seed. RT-PCR applied to mRNA isolated from C. ensiformis tissues confirmed the presence of two genes sharing 86% similarity. Further studies have shown that canatoxin is a Zn/Ni hybrid isoform of urease with about 40% of its ureolytic activity. As described for CNTX, urease also displayed platelet aggregating activity, interaction with glycoconjugates, and entomotoxic effects.  Studies with p-hydroxy-mercuribenzoate, a classical inhibitor of ureases, suggested at least two distinct domains involved in the biological properties of the proteins, as it abolished the ureolytic activity of both isoenzymes without interfering in their interaction with glycoconjugates or the effects on platelets. Our data thus indicate that canatoxin and urease belong to a novel group of multifuncional plant proteins related to defense against insect predation.

Supported by CNPq, PRONEX and FAPERGS

CORRESPONDENCE TO:

CARLINI, C.R., Departamento de Biofísica, IB, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91.501-907, Brasil, Email: ccarlini@vortex.ufrgs.br