Análise de uma sequência de cDNA obtida das sementes de Swartzia grandiflora Bong. Benth que codifica uma lectina

Abstract

Swartzia grandiflora is a legume Swartzieae tribe, a basal taxon of Papilionoideae subfamily, poorly studied in relation to the occurrence and characterization of lectins. The main objective of this study was to obtain cDNA sequences encoding S. grandifloralectins and characterize the encoded structures. As a result, there wereobtained six unique cDNA sequences, encoding six distinct polypeptide chains, termed SGL-A and SGL-F. The primary structures of the proteins deduced from the cDNA sequence had 240 (SGL-A to D) and 244 (SGL-E and -F) amino acid residues. The calculated molecular weight ranged from ~ 26.6 (SGL-A) to ~ 26.9 kDa (SGL-F), whilst the pI predicted from the amino acid sequences varied from 5.22 (SGL-B) to 5.37 (SGL-A,- C and D). When the amino acid sequences were aligned and compared to each other by means of an identity matrix, it was possible to group them into two groups containing 4 (SGL-A to SGL-D, identity = 99.1%) and 2 ( SGL-E and SGL-F; identity = 99.5%) sequences, respectively. The average identity between the sequences of two groups was 53.2%. Considering the great identity between the amino acid sequences of a same group a representative sequence of each was chosen (SGL-A and SGL-E) for further analysis. Search for homologous sequences in the NCBI protein database revealed that SGL-A and SGL-E have similarity with lectins Fabaceae, but with ever higher percentage of identity to 50-51%. This suggests that lectins of S. grandiflora identified in this study constitute a distinct group from the legume lectins characterized to date. Comparisons with the bank of proteins with known three-dimensional structures (PDB) showed greater SGL-A identity (Bit score = 196, E-value = 7e-61, ID = 44%) with a lectin fromPlatypodiumelegans (tribe Dalbergieae) and SGL-E (Bit score = 179, E-value = 1e-54 = 47% identity) with the agglutinin (BMA) of Leucomphalos (Bowringia) mildbraedii (Sophoreae tribe). The alignment of the amino acids sequences SGL-A and SGL-E with such structures has allowed the hypothetical amino acid residues involved in binding divalent cations and the formation of the interaction site with carbohydrates were mapped in their primary structures. Models of three-dimensional structures of SGL-A and SGL-E were generated by comparative modeling using M4T method, and validated against stereochemical parameters. Structural models of both proteins presented in a folding beta barrel, comprising two antiparallel sheets, one with seven tapes and other tapes of five. This folding is characteristic of legume lectins. Molecular docking site directed suggested that D-galactose is a likely binder SGL-A, judging by the favorable total interaction energy (-76.2 kcal / mol) estimated for the protein-ligand complex.