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Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO3 interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices.

An unexplored physical mechanism which produces a magnetoelectric effect in ferroelectric-ferromagnetic multilayers is studied based on first-principles calculations. Its origin is a change in bonding at the ferroelectric-ferromagnet interface that alters the interface magnetization when the electric polarization reverses. Using Fe/BaTiO3 multilayers as a representative model, we show a sizable difference in magnetic moments of Fe and Ti atoms at the two interfaces dissimilar by the orientation of the local electric dipole moments. The predicted magnetoelectric effect opens a new direction to control magnetic properties of thin-film layered structures by electric fields.

We perform an ab initio study of spin-polarized tunneling in epitaxial Co/SrTiO(3)/Co magnetic tunnel junctions with bcc Co(001) electrodes. We predict a large tunneling magnetoresistance in these junctions, originating from a mismatch in the majority- and minority-spin bands both in bulk bcc Co and at the Co/SrTiO(3)/Co interface. The intricate complex band structure of SrTiO(3) enables efficient tunneling of the minority d electrons which causes the spin polarization of the Co/SrTiO(3)/Co interface to be negative in agreement with experimental data. Our results indicate that epitaxial Co/SrTiO(3)/Co magnetic tunnel junctions with bcc Co(001) electrodes are a viable alternative for device applications.

The folding of the extracellular serine protease, alpha-lytic protease (alphaLP; EC 3.4.21.12) reveals a novel mechanism for stability that appears to lead to a longer functional lifetime for the protease. For alphaLP, stability is based not on thermodynamics, but on kinetics. Whereas this has required the coevolution of a pro region to facilitate folding, the result has been the optimization of native-state properties independent of their consequences on thermodynamic stability. Structural and mutational data lead to a model for catalysis of folding in which the pro region binds to a conserved beta-hairpin in the alphaLP C-terminal domain, stabilizing the folding transition state and the native state. The pro region is then proteolytically degraded, leaving the active alphaLP trapped in a metastable conformation. This metastability appears to be a consequence of pressure to evolve properties of the native state, including a large, highly cooperative barrier to unfolding, and extreme rigidity, that reduce susceptibility to proteolytic degradation. In a test of survival under highly proteolytic conditions, homologous mammalian proteases that have not evolved kinetic stability are much more rapidly degraded than alphaLP. Kinetic stability as a means to longevity is likely to be a mechanism conserved among the majority of extracellular bacterial pro-proteases and may emerge as a general strategy for intracellular eukaryotic proteases subject to harsh conditions as well.

alpha-Lytic protease (alphaLP), an extracellular bacterial protease, is synthesized with a large amino-terminal pro-region that is essential for its folding in vivo and in vitro. In the absence of the pro-region, the protease folds to an inactive, partially folded state, designated 'I'. The pro-region catalyses protease folding by directly stabilizing the folding transition state (>26kcal mol(-1)) which separates the native state 'N' from I. Although a basic tenet of protein folding is that the native state of a protein is at the minimum free energy, we show here that both the I and fully unfolded states of alphaLP are lower in free energy than the native state. Native alphaLP is thus metastable: its apparent stability derives from a large barrier to unfolding. Consequently, the evolution of alphaLP has been distinct from most other proteins: it has not been constrained by the free-energy difference between the native and unfolded states, but instead by the size of its unfolding barrier.

The nature of how human gammadelta T cells are normally generated is not clear. We have used an RT-PCR assay and DNA sequencing to identify and compare delta-encoded TCRs (TCRDs) that are generated de novo in the fetal gut, liver, and thymus and to determine when, where, and how the TCRD repertoire is established during normal embryonic development. Rearranged TCRDV genes are first expressed outside of the thymus in the liver and primitive gut between 6 and 9 wk gestation. Although DV1Rs and/or DV2Rs predominated, differences in the pattern of TCRDV gene rearrangement and transcription in each tissue during ontogeny were identified. Specific, DV2-encoded TCRs are highly conserved throughout ontogeny in the tissues from the same and between genetically distinct donors. Although the thymic and intestinal gammadelta T cell repertoires partially overlap early in development, they diverge and become nonoverlapping during the second trimester, and the generation of the intestinal gammadelta T cell repertoire is characterized by differences in the processing of DV1Rs and DV2Rs. Whereas the structural diversity of DV1Rs progressively increases during gut development up to birth, DV2Rs have limited structural diversity throughout ontogeny. Together, our findings provide evidence for the ability of different fetal tissues to support the development of gammadelta T cells.