3J7X: Capsid Expansion Mechanism Of Bacteriophage T7 Revealed By Multi-state Atomic Models Derived From Cryo-em Reconstructions

Many dsDNA viruses first assemble a DNA-free procapsid, using a scaffolding protein-dependent process. The procapsid, then, undergoes dramatic conformational maturation while packaging DNA. For bacteriophage T7 we report the following four single-particle cryo-EM 3D reconstructions and the derived atomic models: procapsid (4.6-A resolution), an early-stage DNA packaging intermediate (3.5 A), a later-stage packaging intermediate (6.6 A), and the final infectious phage (3.6 A). In the procapsid, the N terminus of the major capsid protein, gp10, has a six-turn helix at the inner surface of the shell, where each skewed hexamer of gp10 interacts with two scaffolding proteins. With the exit of scaffolding proteins during maturation the gp10 N-terminal helix unfolds and swings through the capsid shell to the outer surface. The refolded N-terminal region has a hairpin that forms a novel noncovalent, joint-like, intercapsomeric interaction with a pocket formed during shell expansion. These large conformational changes also result in a new noncovalent, intracapsomeric topological linking. Both interactions further stabilize the capsids by interlocking all pentameric and hexameric capsomeres in both DNA packaging intermediate and phage. Although the final phage shell has nearly identical structure to the shell of the DNA-free intermediate, surprisingly we found that the icosahedral faces of the phage are slightly ( approximately 4 A) contracted relative to the faces of the intermediate, despite the internal pressure from the densely packaged DNA genome. These structures provide a basis for understanding the capsid maturation process during DNA packaging that is essential for large numbers of dsDNA viruses.
PDB ID: 3J7XDownload
MMDB ID: 123754
PDB Deposition Date: 2014/8/12
Updated in MMDB: 2014/11
Experimental Method:
electron microscopy
Resolution: 3.8  Å
Source Organism:
Similar Structures:
Biological Unit for 3J7X: 420-meric
Molecular Components in 3J7X
Label Count Molecule
Proteins (420 molecules)
Major Capsid Protein 10A(Gene symbol: T7p45)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB