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Structure of a lectin from Canavalia gladiata seeds: new structural insights for old molecules
Plínio Delatorre1 ,2, Bruno AM Rocha1 ,2, Emmanuel P Souza1, Taianá M Oliveira1, Gustavo A Bezerra1, Frederico BMB Moreno3, Beatriz T Freitas2, Tatiane Santi-Gadelha3, Alexandre H Sampaio1, Walter F Azevedo Jr4 ,5 and Benildo S Cavada1
1Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará, Ceará, Brazil2Departamento de Biologia, Universidade Regional do Cariri, Ceará, Brazil3Departamento de Biologia, Universidade Federal da Paraíba, Paraíba, Brazil4Departamento de Física, IBILCE, Universidade Estadual Paulista, São Paulo, Brazil5Faculdade de Biociências, PUCRS, Av. Ipiranga 6681, Zip Code 90619-900, Porto Alegre, RS, Brazil
Lectins are mainly described as simple carbohydrate-binding proteins. Previous studies have tried to identify other binding sites, which possible recognize plant hormones, secondary metabolites, and isolated amino acid residues. We report the crystal structure of a lectin isolated from Canavalia gladiata seeds (CGL), describing a new binding pocket, which may be related to pathogen resistance activity in ConA-like lectins; a site where a non-protein amino-acid, α-aminobutyric acid (Abu), is bound.
The overall structure of native CGL and complexed with α-methyl-mannoside and Abu have been refined at 2.3 Å and 2.31 Å resolution, respectively. Analysis of the electron density maps of the CGL structure shows clearly the presence of Abu, which was confirmed by mass spectrometry.
The presence of Abu in a plant lectin structure strongly indicates the ability of lectins on carrying secondary metabolites. Comparison of the amino acids composing the site with other legume lectins revealed that this site is conserved, providing an evidence of the biological relevance of this site. This new action of lectins strengthens their role in defense mechanisms in plants.
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