2 research outputs found
Expression, Purification, and Solid-State NMR Characterization of the Membrane Binding Heme Protein Nitrophorin 7 in Two Electronic Spin States
The
nitrophorins (NPs) comprise a group of NO transporting ferriheme <i>b</i> proteins found in the saliva of the blood sucking insect Rhodnius prolixus. In contrast to other nitrophorins
(NP1–4), the recently identified membrane binding isoform NP7
tends to form oligomers and precipitates at higher concentrations
in solution. Hence, solid-state NMR (ssNMR) was employed as an alternative
method to gain structural insights on the precipitated protein. We
report the expression and purification of <sup>13</sup>C,<sup>15</sup>N isotopically labeled protein together with the first ssNMR characterization
of NP7. Because the size of NP7 (21 kDa) still provides a challenge
for ssNMR, the samples were reverse labeled with Lys and Val to reduce
the number of crosspeaks in two-dimensional spectra. The two electronic
spin states with <i>S</i> = 1/2 and <i>S</i> =
0 at the ferriheme iron were generated by the complexation with imidazole
and NO, respectively. ssNMR spectra of both forms are well resolved,
which allows for sequential resonance assignments of 22 residues.
Importantly, the ssNMR spectra demonstrate that aggregation does not
affect the protein fold. Comparison of the spectra of the two electronic
spin states allows the determination of paramagnetically shifted cross
peaks due to pseudocontact shifts, which assists the assignment of
residues close to the heme center
Size and Compositional Effects on Contrast Efficiency of Functionalized Superparamagnetic Nanoparticles at Ultralow and Ultrahigh Magnetic Fields
Magnetic resonance imaging (MRI) systems at ultralow
and ultrahigh
field have been developed for biomedical imaging. We synthesized and
functionalized superparamagnetic (SPM) nanoparticles (NPs) and studied
the spin–lattice (<i>T</i><sub>1</sub>) and spin–spin
(<i>T</i><sub>2</sub>) relaxation time of protons in water
surrounding these NPs at ultralow and at ultrahigh magnetic fields.
In these fields, size and compositional effects of SPM NPs were observed
contributing to the spin–lattice (<i>r</i><sub>1</sub>) and spin–spin (<i>r</i><sub>2</sub>) relaxivities
as well as <i>r</i><sub>2</sub>/<i>r</i><sub>1</sub> ratios. These results reveal the relationship between magnetic characteristics
of SPM NPs and relaxation behavior of water proton at ultralow or
ultrahigh field