3 research outputs found
Epitaxial growth of topological insulator Bi2Se3 film on Si(111) with atomically sharp interface
Atomically sharp epitaxial growth of Bi2Se3 films is achieved on Si (111)
substrate with MBE (Molecular Beam Epitaxy). Two-step growth process is found
to be a key to achieve interfacial-layer-free epitaxial Bi2Se3 films on Si
substrates. With a single-step high temperature growth, second phase clusters
are formed at an early stage. On the other hand, with low temperature growth,
the film tends to be disordered even in the absence of a second phase. With a
low temperature initial growth followed by a high temperature growth,
second-phase-free atomically sharp interface is obtained between Bi2Se3 and Si
substrate, as verified by RHEED (Reflection High Energy Electron Diffraction),
TEM (Transmission Electron Microscopy) and XRD (X-Ray Diffraction). The lattice
constant of Bi2Se3 is observed to relax to its bulk value during the first
quintuple layer according to RHEED analysis, implying the absence of strain
from the substrate. TEM shows a fully epitaxial structure of Bi2Se3 film down
to the first quintuple layer without any second phase or an amorphous layer.Comment: 20 pages, 7 figure
Understanding the Structure–Function Relationship of Lysozyme Resistance in Staphylococcus aureus by Peptidoglycan O‑Acetylation Using Molecular Docking, Dynamics, and Lysis Assay
Lysozyme is an important component
of the host innate defense system.
It cleaves the β-1,4 glycosidic bonds between <i>N</i>-acetylmuramic acid and <i>N</i>-acetylglucosamine of bacterial
peptidoglycan and induce bacterial lysis. Staphylococcus
aureus (S. aureus),
an opportunistic commensal pathogen, is highly resistant to lysozyme,
because of the O-acetylation of peptidoglycan by <i>O</i>-acetyl transferase (<i>oatA</i>). To understand the structure–function
relationship of lysozyme resistance in S. aureus by peptidoglycan O-acetylation, we adapted an integrated approach
to (i) understand the effect of lysozyme on the growth of S. aureus parental and the <i>oatA</i> mutant
strain, (ii) study the lysozyme induced lysis of exponentially grown
and stationary phase of both the S. aureus parental and <i>oatA</i> mutant strain, (iii) investigate
the dynamic interaction mechanism between normal (de-O-acetylated)
and O-acetylated peptidoglycan substrate in complex with lysozyme
using molecular docking and molecular dynamics simulations, and (iv)
quantify lysozyme resistance of S. aureus parental and the <i>oatA</i> mutant in different human
biological fluids. The results indicated for the first time that the
active site cleft of lysozyme binding with O-acetylated peptidoglycan
in S. aureus was sterically hindered
and the structural stability was higher for the lysozyme in complex
with normal peptidoglycan. This could have conferred reduced survival
of the S. aureus <i>oatA</i> mutant in different human biological fluids. Consistent with this
computational analysis, the experimental data confirmed decrease in
the growth, lysozyme induced lysis, and lysozyme resistance, due to
peptidoglycan O<i>-</i>acetylation in S.
aureus