RESUMO
The crystal structure of kinetin dihydrogenphosphate has been determined at 115 and 293 K. Kinetin dihydrogenphosphate undergoes a polymorphic phase transition at 291.1 K. In both phases the crystal belongs to the triclinic system with the symmetry described by the space group P\bar 1. In the low-temperature phase, the unit cell is doubled along the a axis. There is a dynamic equilibrium between different tautomeric forms of the adenine residue, determined by the distribution of H atoms within the network of hydrogen bonds.
Assuntos
Cinetina/química , Cristalografia por Raios X , Citocininas/química , Modelos Moleculares , Estrutura Molecular , Reguladores de Crescimento de Plantas/químicaRESUMO
We analyzed a tertiary structure of systemin, the first identified polypeptide plant hormone, using two-dimensional NMR spectroscopy. From these data and molecular dynamics calculations we concluded that the peptide can adopt a Z-like-beta-sheet structure, which has previously been found in many specific DNA-binding proteins. Using DNA-cellulose affinity chromatography, we showed that systemin binds strongly to DNA. We suggest that the specific systemin-DNA interaction, particularly in a promoter region of the proteinase inhibitors, could effect gene expression and thus explain the biological activity of systemin.
Assuntos
Proteínas de Ligação a DNA/química , DNA/metabolismo , Peptídeos/química , Proteínas de Plantas/química , Inibidores de Proteases/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Cromatografia de Afinidade , Gráficos por Computador , Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica de Plantas , Lactoferrina/metabolismo , Solanum lycopersicum/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Fragmentos de Peptídeos/metabolismo , Peptídeos/metabolismo , Peptídeos/farmacologia , Proteínas de Plantas/metabolismo , Proteínas de Plantas/farmacologia , Dobramento de Proteína , Estrutura Secundária de Proteína , Estrutura Terciária de ProteínaRESUMO
Polymerization of actin by increasing the ionic strength leads to a quenching of almost all 1H NMR signals. Surprisingly, distinct signals with relatively small line widths can still be observed in actin filaments (F-actin) indicating the existence of mobile, NMR visible residues in the macromolecular structure. The intensity of the F-actin spectrum is much reduced if one replaces Mg2+ with Ca2+, and a moderate reduction of the signal intensity can also be obtained by increasing the ionic strength. These results can be explained in a two-state model of the actin promoters with a M- (mobile) state and a I- (immobile) state in equilibrium. In the M-state a number of residues in the actin promoter are mobile and give rise to observable NMR signals. This equilibrium is shifted towards the I-state specifically by replacing Mg2+ with Ca(2+)-ions and unspecifically by addition of monovalent ions such as K+. The binding of phalloidin to its high-affinity site in the filaments does not influence the equilibrium between M- and I-state. Phalloidin itself is completely immobilized in F-actin, its exchange with the solvent being slow on the NMR time scale.
Assuntos
Actinas/química , Músculos/química , Animais , Sítios de Ligação , Cálcio/química , Magnésio/química , Espectroscopia de Ressonância Magnética , Modelos Químicos , Concentração Osmolar , Faloidina/química , Polímeros , Coelhos , ViscosidadeRESUMO
We studied the interaction of wheat germ 5S rRNA with synthetic polypeptides whose amino acid sequences were similar to that of the second zinc finger of Xenopus laevis transcriptional factor IIIA (TFIIIA). The results clearly show that in addition to weak 5S rRNA binding activity (data not shown), these two 30 amino acid long polypeptides hydrolyse some phosphodiester bonds of wheat germ 5S rRNA. The cleavage pattern of plant 5S rRNA is very specific and the cuts occur only after the pyrimidine residues. The same properties of these peptides were furthermore observed for E. coli tRNA(Phe). We found that the digestion specificity of both the zinc finger peptides is very similar to that of a pancreatic ribonuclease (RNase A).
