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Crystal structure of a conserved protease that binds DNA: the bleomycin hydrolase, Gal6
L Joshua-Tor1, H E Xu, S A Johnston
1Divison of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.
Abstract:
Bleomycin hydrolase is a cysteine protease that hydrolyzes the anticancer drug bleomycin. The homolog in yeast, Gal6, has recently been identified and found to bind DNA and to act as a repressor in the Gal4 regulatory system. The crystal structure of Gal6 at 2.2 A resolution reveals a hexameric structure with a prominent central channel. The papain-like active sites are situated within the central channel, in a manner resembling the organization of active sites in the proteasome. The Gal6 channel is lined with 60 lysine residues from the six subunits, suggesting a role in DNA binding. The carboxyl-terminal arm of Gal6 extends into the active site cleft and may serve a regulatory function. Rather than each residing in distinct, separable domains, the protease and DNA-binding activities appear structurally intertwined in the hexamer, implying a coupling of these two activities.
Insights
Bleomycin hydrolase homolog Gal6, a yeast protease, binds DNA and represses gene activity. Its crystal structure reveals intertwined protease and DNA-binding functions within a hexameric complex.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biology
Background:
- Bleomycin hydrolase (BLMH) is a cysteine protease crucial for metabolizing the anticancer drug bleomycin.
- A yeast homolog, Gal6, has been identified with DNA-binding and gene repression roles in the Gal4 regulatory system.
Purpose of the Study:
- To elucidate the structural basis of Gal6's dual protease and DNA-binding functions.
- To understand the molecular mechanisms underlying Gal6's role in gene regulation.
Main Methods:
- X-ray crystallography was used to determine the structure of Gal6 at 2.2 A resolution.
- Structural analysis focused on the arrangement of active sites and DNA-binding surfaces.
Main Results:
- Gal6 forms a hexameric structure with a central channel.
- Papain-like active sites are located within this channel, similar to proteasome organization.
- The channel is rich in lysine residues, indicating a DNA-binding role.
- A carboxyl-terminal arm interacts with the active site cleft, suggesting regulation.
Conclusions:
- The protease and DNA-binding activities of Gal6 are structurally intertwined within the hexamer.
- This structural arrangement implies a functional coupling between enzymatic activity and DNA binding.
- Gal6's structure provides insights into the regulation of gene expression and drug metabolism.