PubMed · 15560123
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Lynne Lederman. 2004. Separation technologies. Supporting solutions.. https://doi.org/10.2144/04375tn01
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Tumor suppressor p53 forms a homo-tetramer through its COOH-terminal oligomerization domain and acts as a sequence-specific transcription factor. We have analysed the interrelation among the transcriptional activities, the structure and the cancer-related mutations in the oligomerization domain by using a comprehensive missense mutation library. Here, we examined the ability of 184 mutant p53s in the domain to form an oligomer by expressing these mutant p53s in yeast, and compared the data with the previous information. We showed that specific residues in the alpha-helix and the beta-strand of the oligomerization domain were critical for both oligomer formation and sequence-specific transactivation, and the activities were closely related. In particular, the alpha-helix was more sensitive to amino-acid substitutions than the beta-strand. We found identity in the interrelation between the two activities, that is, monomer mutants were transcriptionally inactive whereas dimer and tetramer mutants retained their transcriptional activities. In TP53 mutation databases, a small number of mutations have been reported in this domain. Surprisingly, most do not encode p53s defective in functional properties. These results indicate that, although oligomer formation is essential for p53 transactivation function, the inactivation of oligomer formation and therefore the inactivation of transactivation may not be essential for tumor suppression by p53 because they do not lead to oncogenic proteins.
Successive changes of solvent conditions can be used to dissociate and reassociate the triple-helical structure of (1,3)-beta-D-glucans. Ultramicroscopic techniques have revealed a blend of circular and other structures following renaturation. When this solvent exchange process is carried out in the presence of certain polynucleotides, the process creates a novel macromolecular complex. Here, we use size exclusion chromatography (SEC) to study such (1,3)-beta-D-glucan-polynucleotide complexes. Online multi-angle laser-light scattering (MALLS) and refractive index (RI) detectors allowed determination of molecular weight and radius of gyration of the molecules. An ultraviolet (UV) detector allowed specific detection of the polynucleotide. The poly-cytidylic acid (poly C) shifted to coelution with the linear fraction of the scleroglucan following the renaturation of poly C-scleroglucan blends, indicating that poly C is incorporated in linear, but not in circular, structures of scleroglucan. This conclusion was consistent with AFM topographs that revealed a decreased fraction of circular structures upon addition of poly C during the renaturation process. The combined information about radius of gyration (R(g)) and molecular weight (M(w)) allowed us to conclude that the poly C-scleroglucan complexes are more dense and have a higher persistence length than linear scleroglucan triple helixes. The experimentally determined mass per unit length was used as a basis for elucidating possible molecular arrangements within the poly C-scleroglucan complex.
The molecular dynamics of poly(L-lactide) (PLLA) biopolymer was characterized through analyses of 1H and 2H NMR line-shapes and spin-lattice relaxation times at different temperatures. At low temperatures (e.g. 90 K), the methyl group rotation is dominant leading to a significant reduction in the proton second moment. Fast methyl group reorientation occurs at ca. 130 K. In additional to the fast methyl group rotation, hydroxyl groups start to reorient as the temperature increases further, eventually leading to the breakdown of the segments of the biopolymer chains above its glass transition temperature Tg of 323 K. The analyses of the 2H NMR line-shapes indicate that both the methyl and hydroxyl reorientations can be described by the so-called cone model, in which the former has three equilibrium positions with theta(C-D) = 70.5 degrees and phi = 120 degrees while the latter one exhibits two equilibrium positions with theta(O-D) = 78 degrees and phi = 180 degrees .