Flexibility at Gly-194 is required for DNA cleavage and relaxation activity of Escherichia coli DNA topoisomerase I.
The proposed mechanism of type IA DNA topoisomerase I includes conformational changes by the single enzyme polypeptide to allow binding of the G strand of the DNA substrate at the active site, and the opening or closing of the "gate" created on the G strand of DNA to the passing single or double DNA strand(s) through the cleaved G strand DNA. The shifting of an alpha helix upon G strand DNA binding has been observed from the comparison of the type IA DNA topoisomerase crystal structures. Site-directed mutagenesis of the strictly conserved Gly-194 at the N terminus of this alpha helix in Escherichia coli DNA topoisomerase I showed that flexibility around this glycine residue is required for DNA cleavage and relaxation activity and supports a functional role for this hinge region in the enzyme conformational change.
Cheng
Bokun
B
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595, USA.
Feng
Jingyang
J
Gadgil
Sharvari
S
Tse-Dinh
Yuk-Ching
YC
D004264:DNA Topoisomerases, Type I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology; D005998:Glycine; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D004264:DNA Topoisomerases, Type I; D005998:Glycine