17 research outputs found
Structural Studies of the Integral Membrane Protein Human LTC4 Synthase by Electron Crystallography
Structure and function of the membrane protein human leukotriene C4 synthase
Issued as final reportUnited States. Department of Health and Human Service
Structural analysis of microsomal glutathione transferase 1 by electron crystallography
The goals of this project were the two-dimensional crystallization of the
membrane protein microsomal glutathione transferase 1 and the
three-dimensional structure determination by electron crystallography.
Microsomal glutathione transferase 1 is a homotrimeric membrane protein.
The enzyme plays an important role in the detoxication in liver, where
microsomal glutathione transferase 1 conjugates glutathione to a
multitude of hydrophobic electrophiles.
It was found that microsomal glutathione transferase 1 can be induced to
form twodimensional crystals. These crystals are grown by reconstitution
into phospholipid bilayers by detergent removal through dialysis. The
protein forms p21212 crystals after six days of dialysis when it is
reconstituted in the presence of three phospholipid molecules per protein
trimer. Fractional changes below this lipid-to-protein ratio result in a
p6 crystal type. The longevity of the crystals can be improved by
increasing the dialysis time to eight days. Grown at room temperature
(21º C and with an unusually high initial detergent concentration of 1%
Triton X-100, the two-dimensional crystals extend to at least 3-10 [my]m.
Furthermore, conclusions could be drawn about the rate-dependence of the
crystal formation.
Both of these crystal forms are ordered to beyond 3 Å resolution as
judged by electron diffraction of untilted specimens. Initially a
projection map of the p21212 crystals was calculated from images at a
resolution of 4 Å. [alpha]-helical secondary structure was apparent in
the center of the trimer, but an outer protein density belonging to each
monomer could not be identified.
An additional projection map of the p21212 crystal form was calculated of
images as well as electron diffraction patterns at a resolution of 3 Å,
which revealed an additional a-helical density in the outer protein
domains of the trimer as well as an unidentified density.
The protein packing in the projection map of the p6 unit cell, calculated
at 3 Å, showed identical elements of protein packing in both crystal
forms. By comparing the projection structures of both crystal types,
densities indicating ordered lipid headgroups or amino acid side chains
could be identified.
The three-dimensional structure of the p6 crystal form was calculated to
a resolution of 6 from electron diffraction patterns and images with tilt
angles to 60º. The three-dimensional map shows a right-handed
[alpha]-helical bundle. Three of the helices are nearly perpendicular to
the plane of the lipid bilayer and parallel to each other. The fourth
helix is highly tilted, and thus it could not be identified in the
projection map. The four helices could be assigned. The N- and C-terminal
extend into the lumen of the endoplasmic reticulum on the periphery of
the trimer. Helix 2 and helix 3 are connected by a short loop, which also
faces the lumenal side of the membrane. The helices 2-4 appear to be
important in the monomer-monomer contacts within the trimer.
Microsomal glutathione transferase 1 is a member of the MAPEG (Membrane
Associated Proteins in Eicosanoid and Glutathione metabolism)
superfamily. It was suggested that the [alpha]-helical bundle observed
for microsomal glutathione transferase 1 is representative of the
tertiary structures of other members of the MAPEG superfamily
Towards a General Protocol to Form Single-Layered 2D Crystal Sheets of Membrane Proteins for Electron Crystallography.
Assessing Two-dimensional Crystallization Trials of Small Membrane Proteins for Structural Biology Studies by Electron Crystallography
Structural Studies of the Integral Membrane Protein Human LTC4 Synthase by Electron Crystallography
The projection structure of the membrane protein microsomal glutathione transferase at 3 Å resolution as determined from two-dimensional hexagonal crystals
Modular-DNA Programmed Molecular Construction of “Fixed” of 2D and 3D-Au Nanoparticle Arrays
Specifically designed dimeric, planar
trimeric, tetrameric, pentameric,
and 3D hexameric assemblies of Au nanoparticles were constructed from
self-assembling DNA modules that contain disulfide groups, for attachment
to the nanoparticles, and covalently linked 2,5-bis(2-thienyl)pyrrole
(SNS) monomers. Treatment of these arrays with horseradish peroxidase
and H<sub>2</sub>O<sub>2</sub> (HRP/H<sub>2</sub>O<sub>2</sub>) results
in bond formation between the SNS monomers that cross-links or ligates
the DNA modules making the assemblies permanent (“fixed”)
Kinetically Controlled Overgrowth of Ag or Au on Pd Nanocrystal Seeds: From Hybrid Dimers to Nonconcentric and Concentric Bimetallic Nanocrystals
This article describes a systematic study of the nucleation
and
growth of Ag (and Au) on Pd nanocrystal seeds. By carefully controlling
the reaction kinetics, the newly formed Ag atoms could be directed
to selectively nucleate and then epitaxially grow on a specific number
(ranging from one to six) of the six faces on a cubic Pd seed, leading
to the formation of bimetallic nanocrystals with a variety of different
structures. In addition to changing the injection rate of precursor,
we also systematically investigated other reaction parameters including
the capping agent, reductant, and reaction temperature. Our results
suggest that the site-selective growth of Ag on cubic Pd seeds could
be readily realized by optimizing these reaction parameters. On the
basis of the positions of Pd seeds inside the bimetallic nanocrystals
as revealed by TEM imaging and elemental mapping, we could identify
the exact growth pathways and achieve a clear and thorough understanding
of the mechanisms. We have successfully applied the same strategy
based on kinetic control to cubic Pd seeds with different sizes and
octahedral Pd seeds of one size to generate an array of novel bimetallic
nanocrystals with well-controlled structures. With cubic Pd seeds
as an example, we have also extended this strategy to the Pd–Au
system. We believe this work will provide a promising route to the
fabrication of bimetallic nanocrystals with novel structures and properties
for applications in plasmonics, catalysis, and other areas