Peptides show much promise as potent and selective drug candidates. Fusing peptides to a scaffold monoclonal antibody produces a conjugated antibody which has the advantages of peptide activity yet also has the pharmacokinetics determined by the scaffold antibody. However, the conjugated antibody often has poor binding affinity to antigens that may be related to unknown structural changes. The study of the conformational change is difficult by conventional techniques because structural fluctuation under equilibrium results in multiple structures co-existing. Here, we employed our two recently developed electron microscopy (EM) techniques: optimized negative-staining (OpNS) EM and individual-particle electron tomography (IPET). Two-dimensional (2D) image analyses and three-dimensional (3D) maps have shown that the domains of antibodies present an elongated peptide-conjugated conformational change, suggesting that our EM techniques may be novel tools to monitor the structural conformation changes in heterogeneous and dynamic macromolecules, such as drug delivery vehicles after pharmacological synthesis and development.
We have observed a glitch in the Crab pulsar (PSR B0531+21) in the 0.5–10 keV X-ray band with the X-Ray Pulsar Navigation-I (XPNAV-1) satellite. This glitch occurred around 2017 November 8. Observations at radio frequency by the Jodrell Bank observatory and the Lovell telescope have confirmed it to be the largest ever observed. We report the results of X-ray observation of this glitch. The measured rotation frequency increase of the Crab is Δν
0 = (14.3 ± 2.0) × 10−6 Hz, corresponding to a fractional increase of Δν
0/ν
0 = (0.48 ± 0.09) × 10−6. Two transient components in the rotation frequency change are detected: one is the short transient term of Δν
n1 = 6.6 × 10−6 Hz with a timescale of 38.6 days and the other is the very short one of Δν
n2 = −1.35 × 10−6 Hz with a timescale of 2.4 days. The step change in the rotation frequency derivative is determined to be
Hz s−1. We also examine the relationship between the persistent offset
and Δν
0, giving
. No significant X-ray flux changes are observed pre- and post-glitch.
The newly launched X-ray pulsar navigation-I (XPNAV-1) is an experimental satellite of China that is designed for X-ray pulsar observation. This paper presents the initial observation results and aims to recover the Crab pulsar's pulse profile to verify the Xray instrument's capability of observing pulsars in space. With the grazing-incidence focusing type instrument working at the soft X-ray band (0.5-10 keV), up to 162 segments of observations of the Crab pulsar are fulfilled, and more than 5 million X-ray events are recorded. Arrival times of photons are corrected to the solar system barycentre, and the 33 ms pulse period is sought out for Crab. Epoch folding of all the corrected photon times generates the refined pulse profile of Crab. The characteristic two-peak profile proves that the Crab pulsar has been clearly seen, so that the conclusion is made that XPNAV-1's goal of being capable of observing pulsars is achieved.
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