title: Complexes of the uracil-DNA glycosylase inhibitor protein, Ugi, with Mycobacterium smegmatis and Mycobacterium tuberculosis uracil-DNA glycosylases.
abstract: Uracil, a promutagenic base, appears in DNA either by deamination of cytosine or by incorporation of dUMP by DNA polymerases. This unconventional base in DNA is removed by uracil-DNA glycosylase (UDG). Interestingly, a bacteriophage-encoded short polypeptide, UDG inhibitor (Ugi), specifically inhibits UDGs by forming a tight complex. Three-dimensional structures of the complexes of Ugi with UDGs from Escherichia coli, human and herpes simplex virus have shown that two of the structural elements in Ugi, the hydrophobic pocket and the beta1-edge, establish key interactions with UDGs. In this report the characterization of complexes of Ugi with UDGs from Mycobacterium tuberculosis, a pathogenic bacterium, and Mycobacterium smegmatis, a widely used model organism for the former, is described. Unlike the E. coli (Eco) UDG-Ugi complex, which is stable to treatment with 8 M urea, the mycobacterial UDG-Ugi complexes dissociate in 5-6 M urea. Furthermore, the Ugi from the complexes of mycobacterial UDGs can be exchanged by the DNA substrate. Interestingly, while EcoUDG sequestered Ugi into the EcoUDG-Ugi complex when incubated with mycobacterial UDG-Ugi complexes, even a large excess of mycobacterial UDGs failed to sequester Ugi from the EcoUDG-Ugi complex. However, the M. tuberculosis (Mtu) UDG-Ugi complex was seen when MtuUDG was incubated with M. smegmatis (Msm) UDG-Ugi or EcoUDG(L191G)-Ugi complexes. The reversible nature of the complexes of Ugi with mycobacterial UDGs (which naturally lack some of the structural elements important for interaction with the beta1-edge of Ugi) and with mutants of EcoUDG (which are deficient in interaction with the hydrophobic pocket of Ugi) highlights the significance of both classes of interaction in formation of UDG-Ugi complexes. Furthermore, it is shown that even though mycobacterial UDG-Ugi complexes dissociate in 5-6 M urea, Ugi is still a potent inhibitor of UDG activity in mycobacteria.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Narottam
authors.initials: N
authors.lastname: Acharya
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Kumar
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Umesh
authors.initials: U
authors.lastname: Varshney
mesh_terms: D000595:Amino Acid Sequence; D045647:DNA Glycosylases; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000378:metabolism*; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000378:metabolism*; D009699:N-Glycosyl Hydrolases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D011489:Protein Denaturation; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D051981:Uracil-DNA Glycosidase; D014508:Urea; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D014764:Viral Proteins; C027619:uracil-DNA glycosylase inhibitor protein, B. subtilis bacteriophage; D014508:Urea; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D051981:Uracil-DNA Glycosidase