title: A novel zinc snap motif conveys structural stability to 3-methyladenine DNA glycosylase I.
abstract: The Escherichia coli 3-methyladenine DNA glycosylase I (TAG) is a DNA repair enzyme that excises 3-methyladenine in DNA and is the smallest member of the helix-hairpin-helix (HhH) superfamily of DNA glycosylases. Despite many studies over the last 25 years, there has been no suggestion that TAG was a metalloprotein. However, here we establish by heteronuclear NMR and other spectroscopic methods that TAG binds 1 eq of Zn2+ extremely tightly. A family of refined NMR structures shows that 4 conserved residues contributed from the amino- and carboxyl-terminal regions of TAG (Cys4, His17, His175, and Cys179) form a Zn2+ binding site. The Zn2+ ion serves to tether the otherwise unstructured amino- and carboxyl-terminal regions of TAG. We propose that this unexpected "zinc snap" motif in the TAG family (CX(12-17)HX(approximately 150)HX(3)C) serves to stabilize the HhH domain thereby mimicking the functional role of protein-protein interactions in larger HhH superfamily members.
authors.affiliation: Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA.
authors.forename: Keehwan
authors.initials: K
authors.lastname: Kwon
authors.forename: Chunyang
authors.initials: C
authors.lastname: Cao
authors.forename: James T
authors.initials: JT
authors.lastname: Stivers
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology; D001665:Binding Sites; D003035:Cobalt; D017124:Conserved Sequence; D003545:Cysteine / Q000378:metabolism; D045647:DNA Glycosylases; D004260:DNA Repair; D004926:Escherichia coli / Q000201:enzymology; D006639:Histidine / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D013054:Spectrophotometry, Atomic; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism; D016335:Zinc Fingers
chemical_list: D003035:Cobalt; D006639:Histidine; C021565:3-methyladenine-DNA glycosylase; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D015032:Zinc; D003545:Cysteine