Structural studies on peanut lectin
Mande, S.C.; Raghunathan, S.; Salunke, D.M.; Khan, M.I.; Swamy, M.J.; Surolia, A.; Vijayan, M.
Indian Journal of Biochemistry and Biophysics 25(1-2): 166-171
1988
ISSN/ISBN: 0301-1208 PMID: 3181973 Document Number: 322169
The anti-T lectin from peanut (Arachis hypogaea) is a tetrameric protein of Mr 110,000 with four apparently identical subunits. The protein crystallises in an orthorhombic form at neutral pH whereas two monoclinic and one triclinic forms grow at acidic pH. All the forms contain four subunits in the crystal asymmetric unit, although one of the monoclinic forms gave evidence for internal symmetry in the tetrameric protein. Rotation function studies using X-ray diffraction data up to a resolution of 4.5 .ANG. from the orthorhombic form and chemical cross-linking experiments followed by sodium dodecyl sulphate gel electrophoresis, indicate that the tetrameric molecule is a dimer of a dimer with 222 (D2) symmetry. Following reports that peanut lectin is related to other legume lectins by circularly permuted sequence homology, the available amino acid sequence of the lectin has been compared with those of concanavalin A, pea lectin and favin. Peanut lectin is homologous to each of the other three lectins to the extent of about 40%. The metal binding site is conserved in the four proteins, whereas considerable variation exists in the carbohydrate binding region. Glycines which have conformations appropriate for D residues in the other three lectins, remain glycines in peanut lectin also. The results of the sequence comparison suggest that peanut lectin has an overall three-dimensional structure similar to that of concanavalin A, pea lectin and favin, although differences in detail are expected. This conclusion is supported by the preliminary results of cross rotation function studies between peanut lectin and concanavalin A currently being carried out at 4.5 .ANG. resolution. Attempts at complete structure solution using molecular replacement are in progress.