Molecular cloning, expression, and cytokinin (6-benzylaminopurine) antagonist activity of peanut (Arachis hypogaea) lectin SL-I
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Isolation and purification of a α-methyl-mannoside specific lectin (SL-I) of peanut was reported earlier [Singh and Das (1994) Glycoconj J 11:282–285]. Native SL-I is a glycoprotein having ∼31 kDa subunit molecular mass and forms dimer. The gene encoding this lectin is identified from a 6-day old peanut root cDNA library by anti-SL-I antibody and N-terminal amino acid sequence homology to the native lectin. Nucleotide sequence derived amino acid sequence of the re-SL-I shows amino acid sequence homology with the N-terminal and tryptic digests’ amino acid sequence of the native SL-I (nSL-I). Presence of a putative glycosylation (QNPS) site and a hydrophobic adenine-binding (VLVSYDANS) site is also identified in SL-I. Homology modeling of the lectin suggests it to be an archetype of legume lectins. It is expressed as a ~30 kDa apoprotein in E. coli and has the carbohydrate specificity and secondary structure identical to its natural counterpart. The lectin SL-I inhibits cytokinin 6-benzylaminopurine (BA)-induced “delayed leaf senescence” and “cotyledon expansion”. Equilibrium dialysis revealed a single high-affinity binding site for adenine (7.6 × 10−6 M) and BA (1.09 × 10−5 M) in the SL-I dimer and thus suggesting that the cytokinin antagonist effect of SL-I is mediated by the direct interaction of SL-I with BA.
KeywordsPeanut lectin SL-I Gene expression Cytokinin 6-benzylaminopurine Cytokinin antagonist activity
native peanut stem lectin
- Con A
lima bean lectin
- WBA I and WBA II
winged bean basic- and acidic- agglutinin respectively
Phaseolus vulgaris erythroagglutinin
Pterocarpus angolensis man/glc specific seed lectin
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Authors gratefully acknowledge Dr. Souvik Maiti for his guidance in fluorescence studies. Authors also acknowledge the Director of IGIB for providing facilities to carry out this work.
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