70 research outputs found
The robust assembly of small symmetric nano-shells
Highly symmetric nano-shells are found in many biological systems, such as
clathrin cages and viral shells. Several studies have shown that symmetric
shells appear in nature as a result of the free energy minimization of a
generic interaction between their constituent subunits. We examine the physical
basis for the formation of symmetric shells, and using a minimal model we
demonstrate that these structures can readily grow from identical subunits
under non equilibrium conditions. Our model of nano-shell assembly shows that
the spontaneous curvature regulates the size of the shell while the mechanical
properties of the subunit determines the symmetry of the assembled structure.
Understanding the minimum requirements for the formation of closed nano-shells
is a necessary step towards engineering of nano-containers, which will have far
reaching impact in both material science and medicine.Comment: 12 pages, 12 figure
Role of Genome in the Formation of Conical Retroviral Shells
Human immunodeficiency virus (HIV) capsid proteins spontaneously assemble
around the genome into a protective protein shell called the capsid, which can
take on a variety of shapes broadly classified as conical, cylindrical and
irregular. The majority of capsids seen in in vivo studies are conical in
shape, while in vitro experiments have shown a preference for cylindrical
capsids. The factors involved in the selection of the unique shape of HIV
capsids are not well understood, and in particular the impact of RNA on the
formation of the capsid is not known. In this work, we study the role of the
genome and its interaction with the capsid protein by modeling the genomic RNA
through a mean-field theory. Our results show that the confinement free energy
for a homopolymeric model genome confined in a conical capsid is lower than
that in a cylindrical capsid, at least when the genome does not interact with
the capsid, which seems to be the case in in vivo experiments. Conversely, the
confinement free energy for the cylinder is lower than for a conical capsid if
the genome is attracted to the capsid proteins as the in vitro experiments.
Understanding the factors that contribute to the formation of conical capsids
may shed light on the infectivity of HIV particles.Comment: 22 pages, 7 figures in J. Phys. Chem. B, 201
Impact of a non-uniform charge distribution on virus assembly
Many spherical viruses encapsulate their genome in protein shells with
icosahedral symmetry. This process is spontaneous and driven by electrostatic
interactions between positive domains on the virus coat proteins and the
negative genome. We model the effect of the icosahedral charge distribution
from the protein shell instead of uniform using a mean-field theory. We find
that the non-uniform charge distribution strongly affects the optimal genome
length, and that it can explain the experimentally observed phenomenon of
overcharging of virus and virus-like particles
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