Effect of self-association on the structural organization of partially folded proteins: inactivated actin

The propensity to associate or aggregate is one of the characteristic properties of many nonnative proteins. The aggregation of proteins is responsible for a number of human diseases and is a significant problem in biotechnology. Despite this, little is currently known about the effect of self-association on the structural properties and conformational stability of partially folded protein molecules. G-actin is shown to form equilibrium unfolding intermediate in the vicinity of 1.5 M guanidinium chloride (GdmCl). Refolding from the GdmCl unfolded state is terminated at the stage of formation of the same intermediate state. An analogous form, known as inactivated actin, can be obtained by heat treatment, or at moderate urea concentration, or by the release of Ca(2+). In all cases actin forms specific associates comprising partially folded protein molecules. The structural properties and conformational stability of inactivated actin were studied over a wide range of protein concentrations, and it was established that the process of self-association is rather specific. We have also shown that inactivated actin, being denatured, is characterized by a relatively rigid microenvironment of aromatic residues and exhibits a considerable limitation in the internal mobility of tryptophans. This means that specific self-association can play an important structure-forming role for the partially folded protein molecules.     

The Role of Polygalacturonase (PG) in the Ripening of Apple Fruits

Polygalacturonase (PG) activity and changes in respiratory intensity of apple fruits were investigated. The respiratory rate was decreased to a preclimacteric minimum from 30 Aug. to 20 Sept., Then increased to a climacteric peak (20–30 Sept.) and again drop down gradually with approaching the senescence stage. The PG activity was undetectable in a developing fruit until the onset climacteric phase. It rose rapidly after harvest, and reaching its highest level on 27 Oct. Just a month after the climacteric peak. The PG activity fell gradually. The amount of the fractions of pectic acid in fruits changed with the modifications of PG activity. With the ripening of fruits, the content of alcohol-soluble small molecules of pectic acids was increased from 12 to 13 5 mg/100 g of tissue, while the amount of alcohol- insoluble large molecules of pectic acids reduced from 530 to 280/100 g of tissue. PG activity would indicate the destruction of cell walls and the separation of cells. The onset of softening of fruits occurred 20 days after the rise of PG activity. It is supposed that the process of softening is directly controlled by PG activity.     

ST-segment elevation associated with allergic reaction to echocardiographic contrast agent administration

We report a case of an allergic reaction after the administration of an echocardiographic contrast agent which resulted in ST-segment elevation. Hypersensitivity and allergic reactions are known causes of acute cardiovascular events. However, only limited reports are available which suggest the exact mechanism of the occurrence of angina or myocardial infarction during severe allergic reactions. In our case, through invasive imaging (coronary angiography and IVUS) we have shown for the first time a transient coronary spasm in the absence of intra-coronary thrombus and only minimal neointimal hyperplasia.     

SUMOylation and PARylation cooperate to recruit and stabilize SLX4 at DNA damage sites

SUMOylation plays important roles in the DNA damage response. However, whether it is important for interstrand crosslink repair remains unknown. We report that the SLX4 nuclease scaffold protein is regulated by SUMOylation. We have identified three SUMO interaction motifs (SIMs) in SLX4, mutating all of which abrogated the binding of SLX4 to SUMO-2 and covalent SLX4 SUMOylation. An SLX4 mutant lacking functional SIMs is not recruited to PML nuclear bodies nor stabilized at laser-induced DNA damage sites. Additionally, we elucidated a novel role for PARylation in the recruitment of SLX4 to sites of DNA damage. Combined, our results uncover how SLX4 is regulated by post-translational modifications.     

Activating and inhibitory Fcγ receptors in rheumatoid arthritis: from treatment to targeted therapies

Fcγ receptors (FcγRs) bind the constant Fc region of IgG molecules. IgG/antigen-containing immune complexes elicit a variety of effector functions in cells that express activating FcγRs. Because activating FcγRs are present on cells from the innate immune system, such as dendritic cells, monocytes/macrophages and granulocytes, these IgG receptors form a crucial link between the innate and the acquired immune systems. Recently, the ability to detect the inhibitory FcγRIIb on cells has indicated an imbalance between activating and inhibitory FcγRs in rheumatoid arthritis. This progress offers an opportunity to study modulation of FcγR balance and could stimulate development of FcγR-directed immunotherapy.     

Length variation and secondary structure of introns in the Mlc1 gene in six species of Drosophila

A nearly universal feature of intron sequences is that even closely related species exhibit a large number of insertion/deletion differences. The goal of the analysis described here is to test whether the observed pattern of insertion/deletion events in the genealogy of the myosin alkali light chain (Mlc1) gene is consistent with neutrality, and if not, to determine the underlying forces of evolutionary change. Mlc1 pre-mRNA is alternatively spliced, and one constraint is that signals necessary for tissue-specificity of directed splicing must be conserved. If the total length of an intron is functionally constrained, then the distribution of indels on branches of the gene genealogy should reflect a departure from randomness. Here we perform a phylogenetic analysis, inferring ancestral states wherever possible on a phylogeny of 29 alleles of Mlc1 from six species of Drosophila. Observed patterns of indels on the genealogy were compared to those from simulated data, with the result that we cannot reject the null hypothesis of neutrality. A clear departure from a neutral prediction was seen in the excess folding free energy predicted for the introns flanking the alternatively spliced exon. Relative rate tests also suggest a retardation in the rate of Mlc1 sequence evolution in the simulans clade.      

Conservation of alternative splicing and genomic organization of the myosin alkali light-chain (Mlc1) gene among Drosophila species

The Mlc1 gene of Drosophila melanogaster encodes two MLC1 isoforms via developmentally regulated alternative pre-mRNA splicing. In larval muscle and tubular and abdominal muscles of adults, all of the six exons are included in the spliced mRNA, whereas, in the fibrillar indirect flight muscle of adult, exon 5 is excluded from the mRNA. We show that this tissue-specific pattern of alternative splicing of the Mlc1 pre-mRNA is conserved in D. simulans, D. pseudoobscura, and D. virilis. Isolation and sequencing of the Mlc1 genes from these three other Drosophila species have revealed that the overall organization of the genes is identical and that the genes have maintained a very high level of sequence identity within the coding region. Pairwise amino acid identities are 94%-99%, and there are no charge changes among the proteins. Total nucleotide divergence within the coding region of the four genes supports the accepted genealogy of these species, but the data indicate a significantly higher rate of amino acid replacement in the branch leading to D. pseudoobscura. A comparison of nucleotide substitutions in the coding portions of exon 5 and exon 6, which encode the alternative carboxyl termini of the two MLC1 isoforms, suggests that exon 5 is subject to greater evolutionary constraints than is exon 6. In addition to the coding sequences, there is significant sequence conservation within the 5' and 3' noncoding DNA and two of the introns, including one that flanks exon 5. These regions are candidates for cis- regulatory elements. Our results suggest that evolutionary constraints are acting on both the coding and noncoding sequences of the Mlc1 gene to maintain proper expression and function of the two MLC1 polypeptides.      

Role of interleukin-7 in degenerative and inflammatory joint diseases

IL-7 is known foremost for its immunostimulatory capacities, including potent T cell-dependent catabolic effects on bone. In joint diseases like rheumatoid arthritis and osteoarthritis, IL-7, via immune activation, can induce joint destruction. Now it has been demonstrated that increased IL-7 levels are produced by human articular chondrocytes of older individuals and osteoarthritis patients. IL-7 stimulates production of proteases by IL-7 receptor-expressing chondrocytes and enhances cartilage matrix degradation. This indicates that IL-7, indirectly via immune activation, but also by a direct action on cartilage, contributes to joint destruction in rheumatic diseases.