Small terminase couples viral DNA binding to genome-packaging ATPase activity |
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Authors: | Ankoor Roy Anshul Bhardwaj Pinaki Datta Gabriel C Lander Gino Cingolani |
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Institution: | Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 233 South 10th Street, Philadelphia, PA 19107, USA. |
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Abstract: | Packaging of viral genomes into empty procapsids is powered by a large DNA-packaging motor. In most viruses, this machine is composed of a large (L) and a small (S) terminase subunit complexed with a dodecamer of portal protein. Here we describe the 1.75?? crystal structure of the bacteriophage P22 S-terminase in a nonameric conformation. The structure presents a central channel ~23?? in diameter, sufficiently large to accommodate hydrated B-DNA. The last 23 residues of S-terminase are essential for binding to DNA and assembly to L-terminase. Upon binding to its own DNA, S-terminase functions as a specific activator of L-terminase ATPase activity. The DNA-dependent stimulation of ATPase activity thus rationalizes the exclusive specificity of genome-packaging motors for viral DNA in the crowd of host DNA, ensuring fidelity of packaging and avoiding wasteful ATP hydrolysis. This posits?a model for DNA-dependent activation of genome-packaging motors of general interest in virology. |
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