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Figure 6.
Figure 6. Membrane and Genome Architecture
(A) (Left)
Slice through the PM2 electron density. The capsid is blue
(0.8σ), lipid headgroups cyan (0.25σ), acyl-chain region light
red (−1.3σ), and supercoiled DNA green (0.25σ). (Right)
Icosahedral electron density profile. Distances measured from
the particle center along the icosahedral 3-fold axis. IL and OL
mark the inner and outer membrane leaflets, respectively.
(B) Cartoon of PM2 membrane vesicle assembly. (1) Dimers of
protein P3 (magenta) and a monomer of protein P6 (gold) anchored
via transmembrane helices (data not shown) on a patch of
bacterial membrane. (2) Independent P3 dimers interact with
monomeric P6 forming the scaffold building block. (3) Three
building blocks come together by interaction of the P3 α1
helices to form a subassembly corresponding to an icosahedral
facet. (4) P6 molecules of two independent subassemblies
interact, facilitated by interaction with the supercoiled DNA
genome via P6 transmembrane helices (and possibly further
components such as P4). (5) This interaction generates a torque
across the membrane via the P6 helices (depicted as small
gold-colored rectangles), driving the curvature of the membrane.
(6) Recruitment of further P6-P3 subassemblies to the condensed
DNA genome leads to a correctly sized lipid vesicle coated with
P3 and P6, on which the outer protein capsid assembles.
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