PubMed · 4275527
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R Grimaud. 1973. [Current data concerning corrosive esophagitis].. https://pubmed.ncbi.nlm.nih.gov/4275527/
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Human profilins are multifunctional, single-domain proteins which directly link the actin microfilament system to a variety of signalling pathways via two spatially distinct binding sites. Profilin binds to monomeric actin in a 1:1 complex, catalyzes the exchange of the actin-bound nucleotide and regulates actin filament barbed end assembly. Like SH3 domains, profilin has a surface-exposed aromatic patch which binds to proline-rich peptides. Various multidomain proteins including members of the Ena/VASP and formin families localize profilin:actin complexes through profilin:poly-L-proline interactions to particular cytoskeletal locations (e.g. focal adhesions, cleavage furrows). Humans express a basic (I) and an acidic (II) isoform of profilin which exhibit different affinities for peptides and proteins rich in proline residues. Here, we report the crystallization and X-ray structure determination of human profilin II to 2.2 A. This structure reveals an aromatic extension of the previously defined poly-L-proline binding site for profilin I. In contrast to serine 29 of profilin I, tyrosine 29 in profilin II is capable of forming an additional stacking interaction and a hydrogen bond with poly-L-proline which may account for the increased affinity of the second isoform for proline-rich peptides. Differential isoform specificity for proline-rich proteins may be attributed to the differences in charged and hydrophobic residues in and proximal to the poly-L-proline binding site. The actin-binding face remains nearly identical with the exception of five amino acid differences. These observations are important for the understanding of the functional and structural differences between these two classes of profilin isoforms.
Escherichia coli O157:H7, the causative agent of hemorrhagic colitis and hemolytic uremic syndrome, can survive in a highly acidic environment. The acid resistance of this organism, as measured by its ability to survive in low pH, depended on the density of the cells present during the assay. At low cell densities (</=2 x 10(7) ml(-1)), about 100% of the stationary phase cells survived in Luria broth pH 2.5 at 37 degrees C for at least 7 h. The same cultures at high cell densities (2-5 x 10(9) ml(-1)) were about 1000-fold more sensitive under identical conditions. Exponential phase cultures did not exhibit the cell density effect. The increased acid sensitivity at high cell densities was absent in the stationary phase cultures of a rpoS mutant (rpoS::pRR10) of an E. coli O157:H7 strain. Cell density dependent acid sensitivity of the stationary phase cultures was also observed in other enterohemorrhagic E. coli and Shigella strains. The increased acid sensitivity at high cell densities was absent in Gram-positive organisms.
A micellar electrokinetic capillary chromatography (MECC) method for the separation and determination of five components, glycyrrhizic acid (GA), glycyrrhetinic acid (GTA) and 3,4'-dimethoxy-5-hydroxychalone, fermononetin and isoliquiritigenin, in extracts of Glycyrrhiza uralensis Fisch root was developed. Migration behavior of these analytes was studied by the systematic examination of the borate and sodium dodecyl sulfate (SDS) concentrations in the run buffer. The optimum separation for these analytes was achieved using 10 mmol l(-1) of tetraborate and 25 mmol l(-1) of SDS as the running buffer, with 17 kV of applied voltage. All experiments were performed using a 50.0 cm (42.4 cm effective length)x75 microm I.D. of fused-silica capillary. The apparent pKa values of GA and GTA and the binding constants for the association between the above five analytes and SDS were calculated in this study. A comparison of the extraction efficiency for GA and GTA from Glycyrrhiza uralensis Fisch root was made using ethanol, distilled water and chloroform as extraction reagents, respectively. These results provided very useful information to select the proper solvent to extract the desired components in Glycyrrhiza uralensis Fisch. The MECC method established in this paper was employed to analysis the above five active components.