4bil
From Proteopedia
Threading model of the T7 large terminase within the gp8gp19 complex
Structural highlights
FunctionTERL_BPT7 The terminase large subunit acts as an ATP driven molecular motor necessary for viral DNA translocation into empty capsids and as an endonuclease that cuts the viral genome at a unique and precise dsDNA sequence to initiate and to end a packaging reaction (By similarity). The terminase lies at a unique vertex of the procapsid and is composed of two subunits, a small terminase subunit involved in viral DNA recognition (packaging sequence), and a large terminase subunit possessing endonucleolytic and ATPase activities (By similarity). Both terminase subunits heterooligomerize and are docked on the portal protein to form the packaging machine (PubMed:23632014). The terminase large subunit exhibits endonuclease activity and cleaves the viral genome concatemer (By similarity). Once the DNA is packaged, the terminase detaches from the portal and gets replaced by the tail to finish maturation of the virion (PubMed:23632014).[HAMAP-Rule:MF_04147][1] Publication Abstract from PubMedDuring bacteriophage morphogenesis DNA is translocated into a preformed prohead by the complex formed by the portal protein, or connector, plus the terminase, which are located at an especial prohead vertex. The terminase is a powerful motor that converts ATP hydrolysis into mechanical movement of the DNA. Here, we have determined the structure of the T7 large terminase by electron microscopy. The five terminase subunits assemble in a toroid which encloses a channel wide enough to accommodate dsDNA. The structure of the complete connector/terminase complex is also reported, revealing the coupling between the terminase and the connector forming a continuous channel. The structure of the terminase assembled into the complex showed a different conformation when compared to the isolated terminase pentamer. To understand in molecular terms the terminase morphological change we generated the terminase atomic model based on the crystallographic structure of its phage T4 counterpart. The docking of the threaded model in both terminase conformations showed that the transition between the two states can be achieved by rigid body subunit rotation in the pentameric assembly. The existence of two terminase conformations and its possible relation to the sequential DNA translocation may shed light into the molecular bases of the packaging mechanism of bacteriophage T7. Large terminase conformational change induced by connector binding in bacteriophage T7.,Dauden MI, Martin-Benito J, Sanchez-Ferrero JC, Pulido-Cid M, Valpuesta JM, Carrascosa JL J Biol Chem. 2013 Apr 30. PMID:23632014[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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