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Structure of P22 Large terminase nuclease domainStructure of P22 Large terminase nuclease domain
Structural highlights
Publication Abstract from PubMedPackaging of viral genomes into preformed procapsids requires the controlled and synchronized activity of an ATPase and a genome-processing nuclease, both located in the large (L) terminase subunit. In this paper, we have characterized the structure and regulation of bacteriophage P22 L-terminase (gp2). Limited proteolysis reveals a bipartite organization, consisting of an N-terminal ATPase core flexibly connected to a C-terminal nuclease domain. The 2.02 A crystal structure of P22 headful nuclease obtained by in drop proteolysis of full length L-terminase (FL-L-terminase) reveals a central seven-stranded beta-sheet core that harbors two magnesium ions. Modeling studies with DNA suggest the two ions are poised for two-metal ion-dependent catalysis, but the nuclease DNA-binding surface is sterically hindered by a loop-helix (L1-alpha2) motif, which is incompatible with catalysis. Accordingly, the isolated nuclease is completely inactive in vitro, while it exhibits endonucleolytic activity in the context of FL-L-terminase. Deleting the auto-inhibitory L1-alpha2 motif (or just the loop L1) restores nuclease activity to a level comparable to FL-L-terminase. Together, these results suggest that the activity of P22 headful nuclease is regulated by an intramolecular cross-talk with the N-terminal ATPase domain. This cross-talk allows for precise and controlled cleavage of DNA that is essential for genome-packaging. Structure of p22 headful packaging nuclease.,Roy A, Cingolani G J Biol Chem. 2012 Jun 19. PMID:22715098[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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