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Selected AbstractsCrystal structures of the Arabidopsis thaliana proliferating cell nuclear antigen 1 and 2 proteins complexed with the human p21 C-terminal segmentPROTEIN SCIENCE, Issue 5 2009Wojciech Strzalka Abstract The proliferating cell nuclear antigen (PCNA) is well recognized as one of the essential cellular components of the DNA replication machinery in all eukaryotic organisms. Despite their prominent importance, very little biochemical and structural information about plant PCNAs is available, in comparison with that obtained from other eukaryotic organisms. We have determined the atomic resolution crystal structures of the two distinct Arabidopsis thaliana PCNAs (AtPCNA), both complexed with the C-terminal segment of human p21. Both AtPCNAs form homotrimeric ring structures, which are essentially identical to each other, including the major contacts with the p21 peptide. The structure of the amino-terminal half of the p21 peptide, containing the typical PIP box sequence, is remarkably similar to those observed in the previously reported crystal structures of the human and archaeal PCNA-PIP box complexes. Meanwhile, the carboxy-terminal halves of the p21 peptide in the plant PCNA complexes are bound to the protein in a unique manner, most probably because of crystal packing effects. A surface plasmon resonance analysis revealed high affinity between each AtPCNA and the C-terminal fragment of human p21. This result strongly suggests that the interaction is functionally significant, although no plant homologs of p21 have been identified yet. We also discovered that AtPCNA1 and AtPCNA2 form heterotrimers, implying that hetero-PCNA rings may play critical roles in cellular signal transduction, particularly in DNA repair. [source] Poly[diaqua(,-4,4,-bipyridine-,2N:N,)bis(,-cyanido-,2C:N)bis(cyanido-,C)nickel(II)copper(II)]: a metal,organic cyanide-bridged frameworkACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008Olha Sereda The structure of the title compound, [NiCu(CN)4(C10H8N2)(H2O)2]n or [{Cu(H2O)2}(,-C10H8N2)(,-CN)2{Ni(CN)2}]n, was shown to be a metal,organic cyanide-bridged framework, composed essentially of ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains (4,4,-bpy is 4,4,-bipyridine) linked by [Ni(CN)4]2, anions. Both metal atoms sit on special positions; the CuII atom occupies an inversion center, while the NiII atom of the cyanometallate sits on a twofold axis. The 4,4,-bpy ligand is also situated about a center of symmetry, located at the center of the bridging C,C bond. The scientific impact of this structure lies in the unique manner in which the framework is built up. The arrangement of the ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains, which are mutually perpendicular and non-intersecting, creates large channels running parallel to the c axis. Within these channels, the [Ni(CN)4]2, anions coordinate to successive CuII atoms, forming zigzag ,Cu,N[triple-bond]C,Ni,C[triple-bond]N,Cu, chains. In this manner, a three-dimensional framework structure is constructed. To the authors' knowledge, this arrangement has not been observed in any of the many copper(II),4,4,-bipyridine framework complexes synthesized to date. The coordination environment of the CuII atom is completed by two water molecules. The framework is further strengthened by O,H...N hydrogen bonds involving the water molecules and the symmetry-equivalent nonbridging cyanide N atoms. [source] From structure of the complex to understanding of the biologyACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2007Michael G. Rossmann The most extensive structural information on viruses relates to apparently icosahedral virions and is based on X-ray crystallography and on cryo-electron microscopy (cryo-EM) single-particle reconstructions. Both techniques lean heavily on imposing icosahedral symmetry, thereby obscuring any deviation from the assumed symmetry. However, tailed bacteriophages have icosahedral or prolate icosahedral heads that have one obvious unique vertex where the genome can enter for DNA packaging and exit when infecting a host cell. The presence of the tail allows cryo-EM reconstructions in which the special vertex is used to orient the head in a unique manner. Some very large dsDNA icosahedral viruses also develop special vertices thought to be required for infecting host cells. Similarly, preliminary cryo-EM data for the small ssDNA canine parvovirus complexed with receptor suggests that these viruses, previously considered to be accurately icosahedral, might have some asymmetric properties that generate one preferred receptor-binding site on the viral surface. Comparisons are made between rhinoviruses that bind receptor molecules uniformly to all 60 equivalent binding sites, canine parvovirus, which appears to have a preferred receptor-binding site, and bacteriophage T4, which gains major biological advantages on account of its unique vertex and tail organelle. [source] Theoretical CD spectrum calculations of the crown-ether aralkyl-ammonium salt complex,CHIRALITY, Issue 5 2002Armand Lázár Abstract Rotatory strengths of the ,-(1-naphtyl)-ethylammonium perchlorate (NEA)-phenazino-18-crown-6 ether molecular complex is determined theoretically by the coupled oscillator model and using ab initio random phase approximation (RPA) to describe local excitations on the chromophores. The computational results are compared to the experimental circular dichroism (CD) spectrum published previously. The good qualitative agreement between calculated and measured optical rotatory strengths allows one to assign the CD bands of the complex in a unique manner. Chirality 14:377,385, 2002. © 2002 Wiley-Liss, Inc. [source] | ||||||||||