Crystal structure of human V-1 in the apo form

V-1, also known as myotrophin, is a 13 kDa ankyrin-repeat protein that binds and inhibits the heterodimeric actin capping protein (CP), which is a key regulator of cytoskeletal actin dynamics. The crystal structure of V-1 in complex with CP revealed that V-1 recognizes CP via residues spanning several ankyrin repeats. Here, the crystal structure of human V-1 is reported in the absence of the specific ligand at 2.3 Å resolution. In the asymmetric unit, the crystal contains two V-1 monomers that exhibit nearly identical structures (Cα r.m.s.d. of 0.47 Å). The overall structures of the two apo V-1 chains are also highly similar to that of CP-bound V-1 (Cα r.m.s.d.s of <0.50 Å), indicating that CP does not induce a large conformational change in V-1. Detailed structural comparisons using the computational program All Atom Motion Tree revealed that CP binding can be accomplished by minor side-chain rearrangements of several residues. These findings are consistent with the known biological role of V-1, in which it globally inhibits CP in the cytoplasm.

Atom Motion in Solids Following Nuclear Transmutation

Following nuclear decay, a daughter atom in a solid will "stay in place" if the recoil energy is less than the threshold for displacement. At high temperature, it may subsequently undergo long-range diffusion or some other kind of atomic motion. In this paper, motion of 111Cd tracer probe atoms is reconsidered following electron-capture decay of 111In in the series of In3R phases (R= rare-earth). The motion produces nuclear relaxation that was measured using the method of perturbed angular correlation. Previous measurements along the entire series of In3R phases appeared to show a crossover between two diffusional regimes. While relaxation for R= Lu-Tb is consistent with a simple vacancy diffusion mechanism, relaxation for R= Nd-La is not. More recent measurements in Pd3R phases demonstrate that the site-preference of the parent In-probe changes along the series and suggests that the same behavior occurs for daughter Cd-probes. The anomalous motion observed for R= Nd-La is attributed to "lanthanide expansion" occurring towards La end-member phases. For In3La, the Cd-tracer is found to jump away from its original location on the In-sublattice in an extremely short time, of order 0.5 ns at 1000 K and 1.2 ms at room temperature, a residence time too short to be consistent with defect-mediated diffusion. Several scenarios that can explain the relaxation are presented based on the hypothesis that daughter Cd-probes first jump to neighboring interstitial sites and then are either trapped and immobilized, undergo long-range diffusion, or persist in a localized motion in a cage.

Atoms, Molecules, Crystals and Semiconductor Devices

Properties of matter and of electronic devices are described, starting with Bohr’s model of the hydrogen atom. Motion of electrons in a periodic potential is shown to allow energy ranges with free motion separated by energy ranges where no propagating states are possible. Metals and semiconductors are described via Schrodinger’s equation in terms of their structure and their electrical properties. Energy gaps and effective masses are described. The semiconductor pn junction is described as a circuit element and as a photovoltaic device. We now extend Schrodinger’s method to more familiar matter, in the form of atoms, molecules and semiconductors. The solar cell, that produces electrical energy from Sunlight, in fact requires a sophisticated understanding of the semiconductor PN junction.

Hydrogen energy-level shifts induced by the atom motion: Crossover from the Lamb shifts to the motion-induced shifts

When the hydrogen atom moves, the proton current generates a magnetic field which interacts with the hydrogen electron. A simple analysis shows that for the hydrogen velocity [Formula: see text] the dominant interaction between the hydrogen momentum and the electron is of order of [Formula: see text], where [Formula: see text] is the fine structure constant, v is the atom velocity, c is the speed of light and m is the electron mass. Using the Bethe–Salpeter equation, the two velocity-dependent operators of this order are derived. As is well known, the degeneracy of the energy levels with the same principal quantum number, n, and the same quantum number of the total angular momentum, j, but the different orbital angular momenta [Formula: see text] is removed by the radiative corrections (the Lamb shift) that are proportional to [Formula: see text]. It is shown that the velocity-dependent perturbation interactions remove this degeneracy as well. There is, however, an important difference between the Lamb shifts and the energy-level shifts induced by the atom motion. The Lamb shift is the diagonal correction to the energy separately for each of the degenerate states. The velocity-dependent perturbation interactions result in the off-diagonal energy corrections between the mutually degenerate states. The joint effect of these two perturbations, which are essentially different in their origin, is analyzed. Given their order of magnitude, the crossover from the Lamb shifts to the motion-induced shifts should occur at the atom velocity [Formula: see text], where [Formula: see text] is a numerical factor dependent on n and j. An experiment using the orbital motion of the Earth is proposed to test the developed theory.