2 research outputs found
Hepatitis B Virus Capsid Completion Occurs through Error Correction
Understanding capsid assembly is
important because of its role
in virus lifecycles and in applications to drug discovery and nanomaterial
development. Many virus capsids are icosahedral, and assembly is thought
to occur by the sequential addition of capsid protein subunits to
a nucleus, with the final step completing the icosahedron. Almost
nothing is known about the final (completion) step because the techniques
usually used to study capsid assembly lack the resolution. In this
work, charge detection mass spectrometry (CDMS) has been used to track
the assembly of the <i>T</i> = 4 hepatitis B virus (HBV)
capsid in real time. The initial assembly reaction occurs rapidly,
on the time scale expected from low resolution measurements. However,
CDMS shows that many of the particles generated in this process are
defective and overgrown, containing more than the 120 capsid protein
dimers needed to form a perfect <i>T</i> = 4 icosahedron.
The defective and overgrown capsids self-correct over time to the
mass expected for a perfect <i>T</i> = 4 capsid. Thus, completion
is a distinct phase in the assembly reaction. Capsid completion does
not necessarily occur by inserting the last building block into an
incomplete, but otherwise perfect icosahedron. The initial assembly
reaction can be predominently imperfect, and completion involves the
slow correction of the accumulated errors
Chemical and Physical Transformations of Aluminosilicate Clay Minerals Due to Acid Treatment and Consequences for Heterogeneous Ice Nucleation
Mineral dust aerosol is one of the
largest contributors to global
ice nuclei, but physical and chemical processing of dust during atmospheric
transport can alter its ice nucleation activity. In particular, several
recent studies have noted that sulfuric and nitric acids inhibit heterogeneous
ice nucleation in the regime below liquid water saturation in aluminosilicate
clay minerals. We have exposed kaolinite, KGa-1b and KGa-2, and montmorillonite,
STx-1b and SWy-2, to aqueous sulfuric and nitric acid to determine
the physical and chemical changes that are responsible for the observed
deactivation. To characterize the changes to the samples upon acid
treatment, we use X-ray diffraction, transmission electron microscopy,
and inductively coupled plasma–atomic emission spectroscopy.
We find that the reaction of kaolinite and montmorillonite with aqueous
sulfuric acid results in the formation of hydrated aluminum sulfate.
In addition, sulfuric and nitric acids induce large structural changes
in montmorillonite. We additionally report the supersaturation with
respect to ice required for the onset of ice nucleation for these
acid-treated species. On the basis of lattice spacing arguments, we
explain how the chemical and physical changes observed upon acid treatment
could lead to the observed reduction in ice nucleation activity