Specificity of adenine binding to lima bean lectin

Abstract

The interactions between lima bean lectin (LBL) and adenine were examined using a series of synthetic purine analogs. Binding was sensitive to modification at most positions of the purine ring, suggesting a high degree of specificity for adenine binding. Methylation ofthe 6 NH2-group to MeNH-, Me2N- and Me3N+-analogs progressively decreased the binding affinity. Compounds lacking the 6 NH2-group were not bound. Methylation of adenine at N1, N3 or N7 also inhibited binding, indicating specific interactions with these ring nitrogens. In contrast to the previous report that N9-substituted adenines, nucleosides and nucleotides were not bound [Roberts, D. D. and Goldstein, I. J. (1983) J. Biol. Chem. 258, 13820], 9-methyl- and 9-benzyl-substituted adenines were bound to LBL with high affinity. Substitutions at C-2 and C-8 were tolerated and, in some cases, increased the affinity of binding to LBL. Heterotropic interactions between the adenine and 1,8-anilinonaphthalenesulphonate binding sites were also sensitive to modification of the purine ring. 2-Methylthioadenine and 4-aminopyrazolo[3,4-d]pyrimidine showed increased allosteric interaction with 1,8-anilinonaphthalenesulphonate binding, whereas several adenine analogs with a 9-p-nitrobenzyl substituent appeared to be negative effectors of 1,8-anilinonaphthalenesulphonate binding.