EPR OF BLEOMYCIN MODEL COMPLEX

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The binding of Mn to apo lectins is required for their biological functionas carbohydrate-binding proteins. A previous ESEEM study of the Mn site of the lectin from Conavalia ensiformis (Con A) not only demonstrated histidine ligation, but also water ligands that were not resolved in the crystal structure of Con A. Lectins from Dioclea, like those from Conavalia, also binds carbohydrates with high specificity, but with a very different G. A crystal structure of a Dioclea lectin shows an identical carbohydrate-binding site to that of Con A. The difference in the thermodynamics of carbohydrate-binding of the two classes of lectins may be the result of difference in solvent packing that is not resolved in the crystal structure. EPR of five Dioclea lectins (D. rostrata, D. guianensis, D. violacea, D. virgata, D. grandiflora) and one from Cratylia floribunda are compared to those from Conavalia (C. brasiliensis, C. bonariensis and C. ensiformis [Con A]). All except D. rostrata and Cratylia floribunda, exhibit an EPR spectrum similar to that of Con A. ESEEM studies are being conducted to examine the Mn site of these lectins and compared to that of Con A in order to investigate the possibility that difference in water ligation plays a role in the different thermodynamics of carbohydrate-binding of the two classes of lectins.