DNA packaging orders the membrane of bacteriophage PRD1.

Abstract

Bacteriophage PRD1 contains a linear dsDNA genome enclosed by a lipid membrane lying within a protein coat. Determination of the structure of the detergenttreated particle to 2 nm by cryo-electron microscopy and three-dimensional reconstruction has defined the position of the major coat protein P3. The coat contains 240 copies of trimeric P3 packed into positions of local 6-fold symmetry on a T = 25 lattice. The threedimensional structures of the PRD1 virion and a DNA packaging mutant to a resolution of 2.8 nm have revealed specific interactions between the coat and the underlying membrane. The membrane is clearly visible as two leaflets separated by 2 nm and spanned by transmembrane density. The size of the coat does not change upon DNA packaging. Instead, the number of interactions seen between the protein shell and the membrane and the order of the membrane components increase. Thus the membrane of PRD1 plays a role in assembly which is akin to that played by the nucleocapsid in other membrane viruses.

The structure of a thermophilic archaeal virus shows a double-stranded DNA viral capsid type that spans all domains of life

“…The structural organization of the STIV capsid is similar to other viruses with large T numbers such as human adenovirus (27,28), bacteriophage PRD1 (29,30), and the algal virus PBCV-1 (31). The predicted secondary structure of the STIV major capsid protein (see above) is predominately ␤-sheet.…”

Tale of two spikes in bacteriophage PRD1

“…This organization is similar to that of adenovirus, in which the hexameric and pentameric capsid proteins are called hexons and pentons, respectively. Furthermore, the PRD1 P3 fold is similar to that of adenovirus hexon (2,(5)(6)(7)(8). In addition, in both viruses, the stability of the capsid is secured by minor cementing proteins (9)(10)(11)(12), and the receptor-recognition complexes are composed of elongated spikes attached to the pentameric vertex proteins (3,(12)(13)(14)(15).…”

“…The capsid (70 nm in diameter) is composed mainly of one protein, the major capsid protein P3 (43 kDa), which forms pseudohexameric trimers. Two hundred forty copies of these trimers are organized on an icosahedral lattice with pseudo T ϭ 25 triangulation (2). The vertices of the icosahedral capsid lattice are occupied by the minor capsid protein P31 (14 kDa), which forms pentamers in solution (3,4).…”

“…The DNA genome is then translocated into the host cytoplasm (22). It has been suggested that because the viral membrane can form a tube, the tube could serve as a conduit for DNA delivery (2,(22)(23)(24). In addition, P2 seems to stabilize an otherwise labile vertex structure because P2-deficient particles are more prone to membrane-tube formation than wild-type (wt) particles (18).…”

“…The structure of PRD1 has been studied by using electron cryomicroscopy (cryo-EM) combined with three-dimensional (3D) image reconstruction (2,11,25) and, more recently, x-ray crystallography, thereby providing the first atomic insight into a lipid-containing virus (12,26). Both methods rely on icosahedral averaging to increase the signal and facilitate the structure determination.…”