Studies on the Degradation Mechanisms of Proteins and their Derivatives in the Foods

The volatile sulfur components produced by boiling soybean meal hydrolyzates (AMINOSAN-EKI) have been identified as dimethyl sulfide and hydrogen sulfide. No mercaptan or disulfides were detected.

The main precursor of dimethyl sulfide is supposed to be methionine methylsulfonium compound derived from methionine and pectin substances (–COOCH₃) during the hydrolysis of soybean meal by hydrochloric acid.     

Studies on the Degradation Mechanisms of Proteins and their Derivatives in the Foods

Cysteine-aldehyde compounds were prepared by the reactions of l-cysteine with formaldehyde, acetaldehyde, n-butyraldehyde, benzaldehyde and furfural in 50% ethanol solutions. Hydrogen sulfide and ammonia liberated from cysteine-aldehyde compounds in heated aqueous solutions (oil bath : 120°C) were determined. Although thiazolidine derivatives were stable generally in boiling aqueous solution, l-cysteine-furfural compound was unstable and a large amount of hydrogen sulfide compared with other compounds was released.     

Single-Molecule Studies on PolySUMO Proteins Reveal Their Mechanical Flexibility

Proteins with β-sandwich and β-grasp topologies are resistant to mechanical unfolding as shown by single-molecule force spectroscopy studies. Their high mechanical stability has generally been associated with the mechanical clamp geometry present at the termini. However, there is also evidence for the importance of interactions other than the mechanical clamp in providing mechanical stability, which needs to be tested thoroughly. Here, we report the mechanical unfolding properties of ubiquitin-like proteins (SUMO1 and SUMO2) and their comparison with those of ubiquitin. Although ubiquitin and SUMOs have similar size and structural topology, they differ in their sequences and structural contacts, making them ideal candidates to understand the variations in the mechanical stability of a given protein topology. We observe a two-state unfolding pathway for SUMO1 and SUMO2, similar to that of ubiquitin. Nevertheless, the unfolding forces of SUMO1 (∼130 pN) and SUMO2 (∼120 pN) are lower than that of ubiquitin (∼190 pN) at a pulling speed of 400 nm/s, indicating their lower mechanical stability. The mechanical stabilities of SUMO proteins and ubiquitin are well correlated with the number of interresidue contacts present in their structures. From pulling speed-dependent mechanical unfolding experiments and Monte Carlo simulations, we find that the unfolding potential widths of SUMO1 (∼0.51 nm) and SUMO2 (∼0.33 nm) are much larger than that of ubiquitin (∼0.19 nm), indicating that SUMO1 is six times and SUMO2 is three times mechanically more flexible than ubiquitin. These findings might also be important in understanding the functional differences between ubiquitin and SUMOs.     

葡萄糖衍生物的合成及其模拟SOD的活性研究

 合成含有组氨酸的葡萄糖衍生物,其结构经IR、~1H-NMR及~(13)C-NMR分析得以确证,同时还测定了它们的超氧化物歧化酶(SOD)样活性。实验结果表明该衍生物与铜离子形成螯合物后,对超氧负离子自由基有清除作用(但远弱于天然SOD),并且对红细胞膜脂质过氧化有抑制功效。     

Surface Proteins of Gram-Positive Bacteria and Mechanisms of Their Targeting to the Cell Wall Envelope

The cell wall envelope of gram-positive bacteria is a macromolecular, exoskeletal organelle that is assembled and turned over at designated sites. The cell wall also functions as a surface organelle that allows gram-positive pathogens to interact with their environment, in particular the tissues of the infected host. All of these functions require that surface proteins and enzymes be properly targeted to the cell wall envelope. Two basic mechanisms, cell wall sorting and targeting, have been identified. Cell well sorting is the covalent attachment of surface proteins to the peptidoglycan via a C-terminal sorting signal that contains a consensus LPXTG sequence. More than 100 proteins that possess cell wall-sorting signals, including the M proteins of Streptococcus pyogenes, protein A of Staphylococcus aureus, and several internalins of Listeria monocytogenes, have been identified. Cell wall targeting involves the noncovalent attachment of proteins to the cell surface via specialized binding domains. Several of these wall-binding domains appear to interact with secondary wall polymers that are associated with the peptidoglycan, for example teichoic acids and polysaccharides. Proteins that are targeted to the cell surface include muralytic enzymes such as autolysins, lysostaphin, and phage lytic enzymes. Other examples for targeted proteins are the surface S-layer proteins of bacilli and clostridia, as well as virulence factors required for the pathogenesis of L. monocytogenes (internalin B) and Streptococcus pneumoniae (PspA) infections. In this review we describe the mechanisms for both sorting and targeting of proteins to the envelope of gram-positive bacteria and review the functions of known surface proteins.     

Structures of Gα Proteins in Complex with Their Chaperone Reveal Quality Control Mechanisms

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Ubiquitin-Independent Degradation of Proteins in Proteasomes

Proteasomes are large supramolecular protein complexes present in all prokaryotic and eukaryotic cells, where they perform targeted degradation of intracellular proteins. Until recently, it was generally accepted that prior to proteolytic degradation in proteasomes the proteins had to be targeted by ubiquitination: ATP-dependent attachment of (typically four sequential) residues of the low-molecular protein, ubiquitin, which involves the ubiquitin-activating enzyme, ubiquitin-conjugating enzyme, and ubiquitin ligase. Cytoplasmic and nucleoplasmic proteins labeled in this way are then digested in 26S proteasomes. However, it becomes increasingly clear that using this route the cell eliminates only a part of unwanted proteins. Many proteins can be cleaved by the 20S proteasome in an ATP-independent manner and without previous ubiquitination. Ubiquitin-independent degradation of proteins in proteasomes is a relatively new area of studies of the role of the ubiquitin-proteasome system. However, recent data obtained in this direction already correct existing concepts about proteasomal degradation of proteins and its regulation. Ubiquitin-independent proteasome degradation needs the main structural precondition in proteins: the presence of unstructured regions in the amino acid sequences that provide interaction with the proteasome. Taking into consideration that in humans almost half of all genes encode proteins that contain a certain proportion of intrinsically disordered regions, it appears that the list of proteins undergoing ubiquitin-independent degradation will demonstrate a further increase. Since 26S proteasomes account for only 30% of the total proteasome content in mammalian cells, most of the proteasomes exist in the form of 20S complexes. The latter suggests that ubiquitin-independent proteolysis performed by the 20S proteasome is a natural process of removing damaged proteins from the cell and maintaining a constant level of intrinsically disordered proteins. In this case, the functional overload of proteasomes in aging and/or other types of pathological processes, if it is not accompanied by triggering more radical mechanisms for the elimination of damaged proteins, organelles, and whole cells, has the most serious consequences for the whole organism.     

Studies on the Photolysis of Sulfur Containing Compounds in Foods

The aqueous solutions of 2-alkyl-thiazolidine-4-carboxylic acids and mercaptals of l-cysteine were exposed to sunlight in the presence of a small amount of riboflavin. Hydrogen sulfide, ammonia, carbon dioxide and carbonyl compounds were the photolysis products.

As for the carbonyl compounds, formaldehyde and acetaldehyde were identified from thiazolidine-4-carboxylic acid and djenkolic acid, acetaldehyde from 2-methyl-thiazolidine-4-carboxylic acid and l-cysteine-mercaptal of acetaldehyde, and acetaldehyde and n-butyraldehyde from 2-n-propyl-thiazolidine-4-carboxylic acid and l-cysteine-mercaptal of n-butyraldehyde.     

Studies on the Photolysis of Sulfur Containing Compounds in Foods

S-Alkyl-l-cysteines in aqueous solutions were exposed to sunlight in the absence and presence of riboflavin. Ammonia, carbon dioxide, acetaldehyde and alkyl mercaptans were detected in the solutions containing a small amount of riboflavin.     

Heterogenous Degradation of Myofibrillar Proteins

Pectic substances were extracted from the vegetables with oxalate buffer of pH 4.25 and, after saponification, fractionated into two components, weakly acidic pectic polysaccharide (WAP) and pectic acid, by DEAE-cellulose and Sephadex G-100 chromatographies. The galacturonic acid content (17.3~25.8%) of WAPs was much lower than that of pectic acids, though the neutral sugar compositions of both pectic substances were almost the same. The arabinose-galactose side chains were found to be very long or highly branched in WAPs compared with those in pectic acids.

All the WAPs were appreciably hydrolyzed by exo- and endopolygalacturonases. The limited-degradation products (the residual polysaccharides; i.e., the rhamnogalacturonan segments) obtained by endopolygalacturonase from both WAPs and pectic acids showed a similar behavior on Sephadex G-100 and Sepharose CL-4B gel filtrations; each of the rhamnogalacturonan segments was eluted in the void volume of the Sephadex G-100 column. From these results, we concluded that WAPs are probably an inherent pectic component of the cell walls of the vegetables.     

大豆异黄酮及其在保健食品中的应用

综述了大豆异黄酮的组成,结构,含量,生理功能及其研究进展,加工对大豆制品中异黄酮的影响以及大豆异黄酮在保健食品中的应用。     

BAR结构域蛋白质的功能

近期对果蝇双载蛋白(amphiphysin)BAR结构域晶体结构的报道,使得BAR结构域研究成为热点。虽然在序列水平上保守性较低,但双载蛋白的BAR结构域与Arfaptin 2的GTP酶结合结构域在结构上极为相似。通过对两种蛋白质的BAR结构域同源序列进行检索分析,发现了大量含BAR结构域相关蛋白质。研究发现,BAR结构域蛋白质多数都参与细胞内物质转运及胞吞作用;BAR结构域不仅可以通过其二聚化基元感知和诱导膜的弯曲,而且某些蛋白质的BAR结构域还具有与小GTP酶结合的功能。     

视黄醇结合蛋白及其基因的分子生物学

视黄醇结合蛋白（RBP）是一类维生素A（VitA）的运载蛋白,参与血清和细胞内视黄醇/视黄酸的转运,是疏水小分子结合蛋白家族的成员。这类RBP主要在肝脏中合成并释放入血液进而进入各种组织。血清RBP通过与视黄醇、前白蛋白及细胞表面受体相互作用,在VitA 的储存、代谢、转运到周围靶器官中具有重要功能;细胞RBP则主要在细胞内发挥类似作用。本文介绍了视黄醇结合蛋白的作用机理、组织定位和发育性表达,还介绍了视黄醇结合蛋白基因的结构、染色体定位以及与动物繁殖性能的关系。Abstract: Retinol-binding proteins (RBPs) are a kind of circulating carrier proteins for serum and cellular retinol and retinol acid, which are lipid-soluble vitamins, and are members of hydrophobic binding protein family. Serum RBPs were synthesized primarily in liver, then was released into blood streams, and then to various tissues. Under the interaction with substances such as retinol, pre-albumin and the receptors of cellular surface, they play important roles in storage, metabolism of VitA and transport of VitA to the target cells. Cellular RBPs play the similar function as serum RBPs in intracell. This review introduces action mechanism, tissue localization and developmental expression of retinol-binding proteins. This review also introduces the structure, chromosome mapping and their relationships with reproductive performance of retinol-binding protein genes.     

Studies on Menthol Derivatives

(–)-Menthyl carbinol (1-(R)-methyl-3-(R)-hydroxymethyl-4-(S)-isopropylcyclohexane) (4) was prepared stereospecifically in good yield by treatment of formaldehyde with the Grignard reagent from (–)-menthyl chloride (2), which was prepared from (–)-menthol-(1-(R)-methyl-3-(R)-hydroxy-4-(S)-isopropylcyclohexane) (1) by chlorination using the Lucas reagent (HCl+ZnCl₂). The configuration of 4 was assigned by the chemical method.     

细菌mRNA的降解机制

在细菌中,mRNA降解具有重要的意义,它不仅可以再循环核苷酸,而且还可以根据生长条件的变化调控基因表达.细菌mRNA的降解机制可以分为3种：① mRNA的一般降解途径|② mRNA的质量控制途径|③ 小RNA介导的降解途径. 这些途径有些与真核生物的mRNA降解途径存在很大差异,有些在真核生物中消失了. 另外,mRNA降解途径还可以直接调控细菌致病因子的表达,这使得细菌mRNA的降解途径很有希望成为药物研发的新靶标,或疫苗制备的新平台,以应对越来越严重的细菌耐药性问题.本文综述了细菌mRNA的降解机制,并对其应用前景进行了展望.     

LEA蛋白的分类与功能研究进展

胚胎发育晚期丰富蛋白(late embryogenesis abundant proteins,LEA蛋白)具有广泛的生物学功能,低温、干旱、盐渍及ABA等均可以诱导LEA蛋白的表达,LEA蛋白的显著特点是具有较高的亲水性与热稳定性.根据LEA蛋白结构特征可将其分为不同的家族,研究发现LEA蛋白具有清除活性氧自由基、稳定膜结构和保护酶活性等功能.介绍LEA蛋白的分类依据、功能和基因表达调控等方面研究的进展.