Over 23,000 isoprenoid compounds have been identified so far. They are known to play various important roles in cellular machinery, and all of them are synthesized through prenyldiphosphate compounds. These compounds are sub-classified into two families, cis- and trans-prenyldiphosphates, based on their geometric isomerism. Each isomer is synthesized by cis- and trans-prenyltransferases, respectively. This paper describes the structure and the reaction mechanism of a cis-prenyltransferase, undecaprenyl diphosphate synthase (UPP synthase), in comparison with those of trans-prenyltransferases. Despite the chemical similarity of the cis- and trans- reactions, the structures and the substrate recognition modes are quite different between each enzyme family.
TransLesion Synthesis (TLS) is a DNA damage tolerance mechanism that allows continued DNA synthesis, even in the presence of damaged DNA templates. In response to DNA damage, TLS polymerases are recruited to replication forks via interactions with ubiquitinated Proliferating Cell Nuclear Antigen (PCNA) involving PCNA-interacting protein box (PIP-box) and ubiquitin-binding domains (UBDs). We now report the first crystal structures of human PCNA in complex with three TLS polymerase peptides containing the non-canonical PIP-box. TLS polymerases interact with PCNA in different ways, both from one another and from canonical PIP-box peptides. Furthermore, we discuss these TLS polymerases interact with ubiquitinated PCNA.
Crystal structures of the phase-change recording material, GeTe-Sb2Te3, pseudo-binary compounds have been investigated over a decade using synchrotron radiation and the large Debye-Scherrer camera installed at SPring-8’s BL02B2 beamline. These compounds can be crystallized into metastable single phase with NaCl-type structure, for instance, by instantaneous laser irradiation; however, they are transformed into stable phases with long period trigonal structures characterized by the chemical formula, (GeTe)n(Sb2Te3)m (n, m; integer) after sufficient heat treatments. These stable phases can be described as structure with cubic close-packing periodicity (…ABCABC…) where the stacking rules of the Ge/Sb and Te layers are different from each other.
Almost impurity- and defect-free barium titanate (BaTiO3) nanoparticles with various sizes from 20 to 430 nm were prepared using 2-step thermal decomposition method. The powder dielectric measurement method indicated that the dielectric permittivity of BaTiO3 particles with a particle size of 140 nm exhibited a dielectric maximum of 5,000. Nano-structures of BaTiO3 nanoparticles were analyzed using a composite structure model. It was found that BaTiO3 nanoparticles had a composite structure consisting of (i) inner tetragonal core, (ii) gradient lattice strain layer (GLSL) and (iii) surface cubic layer. The crystal structure of each region didn’t depend on particle size while the volume fraction of the GLSL and the surface cubic layer increased with decreasing the particle size. These results suggested that the size effect of BaTiO3 nanoparticles originated from the composite structure.