Th. Li et al., CARBOHYDRATE MINOR-GROOVE INTERACTIONS IN THE BINDING OF CALICHEAMICIN GAMMA-1(I) TO DUPLEX DNA, Journal of the American Chemical Society, 116(9), 1994, pp. 3709-3715
The sequence-specific DNA cleavage activity of calicheamicin gamma(1)(
I) was studied using a synthetic 20mer DNA substrate that contains a s
ingle TCCT.AGGA target site. The cleavage reaction was initiated by ad
dition of beta-mercaptoethanol, which, under conditions of calicheamic
in excess, results in burst kinetics. The burst amplitude was used to
obtain a K-D value of 135 nM for the calicheamicin-DNA interaction. Ca
licheamicin and calicheamicin oligosaccharide were allowed to compete
for binding, which provided a K-I value of 4.1 mu M for the oligosacch
aride-DNA interaction. Replacement of the iodo-substituted oligosaccha
ride by the corresponding bromo-, chloro-, fluoro-, methyl-, and hydro
gen-substituted compounds resulted in progressively weaker binding. Re
placement of guanine by inosine at the 5'-most but not the 3'-most pos
ition within the AGGA target sequence resulted in greatly diminished D
NA cleavage. These results suggest that for this target sequence there
is a critical interaction between the iodine substituent on the calic
heamicin oligosaccharide and the 5'-most guanine C2-NH2 group within t
he minor groove of the target DNA.