STUDIES ON THE PORE FORMATION MECHANISM OF β-CRYSTALLINE POLYPROPYLENE UNDER STRETCHING

The pore formation mechanism of β-crystalline polypropylene under stretching was investigated. The porosity of the samples increases rapidly with stretching, having a maximum at draw ratios around 2 and then decreases monotonically. An abrupt formation process of initial micropores at very low draw ratios was evidenced by in situ SAXS measurements. At the same time the phase transition from β-crystal to α-crystal proceeds slowly in the whole deformation process up to large draw ratios around 5. Comparative studies of α-and β-crystalline polypropylene samples before stretching indicate that in addition to difference in crystal forms the α-and β-crystalline polypropylene samples exhibit quite different morphological features. There are a lot of interfaces in β-crystalline polypropylene samples, which may have a lower density value and can be easily etched by argon ions and penetrated by small molecules. It was concluded from these experimental facts that the pore formation and crystal transition are two independent phenomena during the deformation of β-crystalline polypropylene samples, and phase transition from β-crystal to α-crystal could hardly be the origin of pore formation. A defect initiation mechanism was proposed to understand the pore formation behavior of β-crystalline polypropylenes.

MULTIPLE MELTING BEHAVIOR OF β-CRYSTALLINE PHASE POLYPROPYLENE

Differential scanning calorimetry and X-ray diffraction experiments on β-nucleated polypropylene were made on the samples crystallized at different temperatures and processed by injection molding. The crystal perfection was shown to vary with crystallization temperature. The observed multiple peaks could be related to a ill-phase with defective inclination of the chains, a recrystallized or original β_2-phase of more perfect inclination, and the α-phase. Injection molded samples could be analyzed from the established DSC interpretation.

Structure and interactions in α-crystallin probed through thiol group reactivity

a-Crystallin is the major structural protein of eye lens of vertebrates. In human lens, the ratio of aA-crystallin to aB-crystallin was found to be 3:1. aA-Crystallin contains two cysteine residues at positions 131 and 142, which are at the junction between the a-crystallin domain and the C-terminal tail. We used the accessibility of the thiol groups by Ellman’s reagent (DTNB) as a tool to gain information about the various structural perturbations of hinge region of a-crystallin and during the binding with substrates. In the native condition, the cys-142 though reacted quite fast was not fully exposed. Several reagents were used to see the accessibility of cys-131. Rate constant for cys-131 was increased gradually with increase in the concentration of reagents. The bindings of substrates are affected by the accessibility of thiol indicating that the substrates bind to the hinge region of a-crystallin. By blocking of cys-142, it was observed that the accessibility of one thiol depends on the other thiol, and they are not independent. The hinge region of a-crystallin is very important as substrate binding site and from this study we have got various structural information about that region.

Comparative Studies of the Carbohydrate of Human Gamma-Crystallins from Fetal and Adult Lenses with Agglutinins

Using gel chromatography of Sephadex G-75 superfine connectedwith Sephadex G-50 fine column,three human γ- crystallins(γ1,γ2,γ3)couldbe obtained.Seven agglutinins(LCA,SBA,DBA,PNA,BSL,RCA and UEA)were used to detect the sugar of sub-γ-crystallins,which had been transferredto nitrocellulose membrane and finally stained with ABC reagents and the sub-strate of HPR.These results suggested that γ2-and γ3-crystallin contain sugar,but γ1-crystallin has no sugar.There is a decrease of carbohydrate of γ2 and γ3as...

Potassium Iodide and Acrylamide Fluorescence Quenching Studies on Gamma-Crystallins of Human Lenses in Development and Aging

γ_1-γ_2-and γ_3-crystallin(corresponding to γs-,γC-and γD- crys-tallin respectively)of human fetal,2 year and 20^+ year old lenses areseparated by Sephadex gel chromatography.lodide and acrylamide are usedto quench the tryptophane fluorescence of sub-γ-crystalline fractions and Ksvand fa values are calculated.The results show that iodide has no clear quench-ing effects on all γ-crystallins,the quenching effects of acrylamide on the tryp-tophan fluorescences of γ1-γ2-and γ3-crystallin from lenses of the ...

视网膜α-crystallins在增生性视网膜疾病中的研究进展

α-crystallins是小分子热休克蛋白家族(small-molecule heat shock protein,sHSP)的重要成员,包括αA-crystallin和αB-crystallin,在各类组织细胞中具有细胞保护和分子伴侣功能。近年来,多项研究发现,视网膜组织α-crystallins可利用自身特性通过各种途径参与增生性视网膜病的血管新生、上皮/内皮细胞间质化等过程。本文主要介绍α-crystallins,尤其是αB-crystallin调节增生性视网膜疾病发展的分子机制,探讨其潜在的临床应用价值。

Identification of the preferentially targeted proteins by carbamylation during whole lens incubation by using radio-labelled potassium cyanate and mass spectrometry

AIMTo attempt to identify the primary targets of carbamylation in bovine lenses incubated under physiological condition.

Computer construction and analysis of protein models of the mutant γD-crystallin gene

Background γD-crystallin plays an important role in human cataract formation. Being highly stable, γD-crystallin proteins are composed of two domains. In this study we constructed and analyzed protein models of the mutant γD-crystallin gene, which caused a special fasciculiform congenital cataract affecting a large Chinese family. Methods γD-crystallin protein structure was predicted by Swiss-Model software using bovine γD-crystallin as a template and Prospect software using human βb2-crystallin as a template. The models were observed with a Swiss-Pdb viewer.Results The mutant γD-crystallin structure predicted by the Swiss-Model software showed that proline23 was an exposed surface residue and P23T change made a decreased hydrogen bond distance between threonine23 and asparagine49. The mutant γD-crystallin structure predicted by the Prospect software showed that the P23T change exerted a significant effect on the protein’s tertiary structure and yielded hydrogen bonds with aspartic acid21, asparagine24, asparagine49 and serine74.Conclusion The mutant γD-crystallin gene has a significant effect on the protein’s tertiary structure, supporting that alteration of γ-crystallin plays an important role in human cataract formation.

Cataract-causing mutation S228P promotes βB1-crystallin aggregation and degradation by separating two interacting loops in C-terminal domain

β/γ-Crystallins are predominant structural proteins in the cytoplasm of lens fber cells and share a similar fold composing of four Greek-key motifs divided into two domains. Numerous cataract-causing mutations have been identified in various β/γ-crystallins, but the mech- anisms underlying cataract caused by most mutations remains uncharacterized. The S228P mutation in βB1- crystallin has been linked to autosomal dominant con- genital nuclear cataract. Here we found that the S228P mutant was prone to aggregate and degrade in both of the human and E. coli cells. The intracellular S228P aggregates could be redissolved by lanosterol. The S228P mutation modified the refolding pathway of βB1- crystallin by affecting the formation of the dimeric intermediate but not the monomeric intermediate. Compared with native βBl-crystallin, the refolded S228P protein had less packed structures, unquenched Trp fluorophores and increased hydrophobic exposure. The refolded S228P protein was prone to aggregate at the physiological temperature and decreased the protective effect of βB1-crystallin on βA3-crystallin. Molecular dynamic simulation studies indicated that the mutation decreased the subunit binding energy and modified the distribution of surface electrostatic potentials. More importantly, the mutation separated two interacting loops in the C-terminal domain, which shielded the hydrophobic core from solvent in native βB1-crystallin. These two interacting loops are highly conserved in both of the N- and C-terminal domains of all β/γ-crys- tallins. We propose that these two interacting loops play an important role in the folding and structural stability of β/γ-crystallin domains by protecting the hydrophobic core from solvent access.

Characterization of three transcripts encoding small heat shock proteins expressed in the codling moth, Cydia pomonella （Lepidoptera： Tortricidae）

Codling moth is a major pest of apples and pears worldwide. Increasing knowledge of how this insect responds to environmental stress will improve field and postharvest control measures used against it. The small heat shock proteins （sHsps） play a maj or role in cellular responses to environmental stressors. A degenerate oligonucleotide primer, designed against the conserved α-crystallin domain, was used in 3＇ rapid amplification of complementary DNA （cDNA） ends reactions to amplify transcripts encoding sHsps expressed in the codling moth cell line, Cp169, subjected to heat shock. Three full-length cDNAs were cloned from Cp169 cells that contained open reading frames encoding sHsps. The cDNA for CpHsp 19.8 was 795 bp encoding 177 amino acids. The cDNA for CpHsp 19.9 was 749 bp encoding 175 amino acids. The cDNA for CpHsp22.2 was 737 bp encoding 192 amino acids. Analysis of the protein sequences of the three CpHsps indicated the presence of 83 amino acids with homology to the α-crystallin domain. For each of the CpHsps, the α-crystallin domain was surrounded by divergent N- and C-terminal regions, consistent with the conserved structural features of sHsps. Real-time polymerase chain reaction, used to determine the expression patterns of each of the sHsps in different developmental stages of codling moth revealed the presence of transcripts in all stages tested. Consistent with characteristics of other sHsps, expression of CpHsp transcripts were greatly enhanced when insects were subjected to heat shock. The results of this research can be used as a guide to study the roles of sHsps in codling moth control using various post-harvest treatments.