The link proteins

Aggregates of chondroitin-keratan sulfate proteoglycan (aggrecan) and hyaluronic acid (hyaluronan) are the major space-filling components of cartilage. A glycoprotein, link protein (LP; 40–48 kDa) stabilizes the aggregate by binding to both hyaluronic acid and aggrecan. In the absence of LP, aggregates are smaller (as estimated by rotary shadowing of electron micrographs) and less stable (they dissociate at pH 5) than they are in the presence of LP. The proteoglycan aggregate, including LP, is dissociated in the presence of chaotropes such as 4 M guanidine hydrochloride. On removal of the chaotrope, the complex will reassociate. This forms the basis of the isolation of LP from cartilage and has been described in detail elsewhere. Tryptic digestion of the proteoglycan aggregates results in a high molecular weight product that consists of hyaluronic acid to which is bound LP and the N-terminal globular domain of aggrecan (hyaluronic acid binding region; HABR) in a 11 stoichiometry. The amino acid sequences of LP and HABR are surprisingly similar. The amino acid sequence can be divided into three domains; an N-terminal domain that falls into the immunoglobulin super-family and two C-terminal domains that are similar to each other. The DNA structure echoes this similarity, in that the major domains are reflected in three separate exons in both LP and HABR. The two C-terminal domains are largely responsible for the association with HA and are related to two recently described hyaluronate-binding proteins, CD44 and TSG-6. A variety of approaches, including analysis of the forms of LP found in vivo, rotary shadowing and analysis of the sequence in the immunoglobulin-like domain, have shed considerable light on the structure-function relationships of LP. This review describes the structure and function of LP in detail, focusing on what can be inferred from the similarity of LP, HABR and related molecules such as immunoglobulins and lymphocyte HA-receptors.     

AB型新单体及PBO树脂制备的新技术及其发展

研究以4,6-二硝基间苯二酚(DNR)和对苯二甲酸单甲酯(TAM)为原料,经三个单元过程合成AB型新单体:2-(对甲氧羰基苯基)-5-氨基-6-羟基苯并噁唑(MAB),进而均缩聚反应制备聚对苯撑苯并二噁唑(PBO)的新路线和新方法,设计了AB型新单体的产业化方案、并阐述了优于AA型单体4,6-二氨基间苯二酚(DAR)路线的特点;同时针对现有PBO技术中存在的问题,提出解决的方法和研究思路,最后对进一步发展AB型新单体:如4-(5-氨基-6-羟基-2-苯并噁唑)苯甲酸(ABA)和H2N-[PBO重复单元]-COOH结构等单体、以及高性价比PBO树脂的研究内容作了建议。     

Mechanoelectrical transduction, ion movement and water stasis in uromodulin.

Mechanical movement of a column of the urinary glycoprotein uromodulin modulates an applied voltage. This change is a property of the glycoprotein and its interaction with the walls of the container and is related to its capacitance. The voltage modulation is not accompanied by changes in rotationally restricted water as has been reported for hyaluronic acid. Diffusion experiments with tritiated water also support the hypothesis that uromodulin acts as a water barrier, but allows ion movement.     

Mechanoelectrical transduction,ion movement and water stasis in uromodulin

Mechanical movement of a column of the urinary glycoprotein uromodulin modulates an applied voltage. This change is a property of the glycoprotein and its interaction with the walls of the container and is related to its capacitance. The voltage modulation is not accompanied by changes in rotationally restricted water as has been reported for hyaluronic acid. Diffusion experiments with tritiated water also support the hypothesis that uromodulin acts as a water barrier, but allows ion movement.     

Der Hyaluronsäuregehalt und die «Hyaluronidase»-Aktivität der Leukozyten

Summary The hyaluronic acid content of leucocytes from the peritoneum of rats shows a significant concentration when measured either turbidimetrically or oxydimetrically, the average value calculated for wet weight being 0.7–0.8%. The hyaluronic acid break down capacity of the leucocytes is not a specific enzyme action but can be attributed to their high ascorbic acid content. The phenomenon has no well defined pH or temperature optimum and can be inhibited by oxine and by semicarbazide.     

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.     

The synovial fluid hyaluronic acid in rheumatoid arthritis

Summary The intrinsic viscosity of hyaluronic acid in synovial fluid decreases significatively in mild and severe arthritis (24% and 37% respectively). Variation in hyaluronic acid concentration parallels the above results. Chondroitin-6-sulfate can be detected in about 30% of the arthritic fluids.This work was partially supported by the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.     

Extraction and purification of brain glycoprotein NSA3 by binding with hyaluronic acid

Brain glycoprotein NSA3 was found to bind to immobilised hyaluronic acid. The binding was reversible and gave pure antigen (99%) in high yields (80%). The binding was suppressed by incubating the affinosorbent with hyaluronidase. It was not suppressed by trypsin. The presence of glycosaminoglycans other than hyaluronic acid in the sample did not inhibit the binding. This property is relevant to those already known for the brain glycoprotein NSA3, and to its localisation at the nodes of Ranvier. We propose to coin the name hyaluronectin for the brain glycoprotein NSA3.     

Histochemical localization of alkaline and acid phosphatase activities in the skin ofMystus (Mystus) vittatus Bl. (Siluriformes)

Summary An attempt has been made to localize alkaline and acid phosphatase activities in the skin ofMystus vittatus by using histochemical techniques. The alkaline phosphatase activity is found in metabolically active cells such as basal columnar cells, mucous cells and polygonal support cells. The acid phosphatase activity is intense in the outermost squamous support cells and in the basal columnar cells. These activities have been correlated with some physiological functions of the epidermis.Acknowledgment. We are thankful to P. Vishwanatham, Government College, Mhow, and Dr R.S. Shrivastava, Holkar Science College, Indore, for providing laboratory facilities and to the Council of Scientific and Industrial Research, New Delhi, for a fellowship for M.S.     

On the structural definition of amyloid fibrils and other polypeptide aggregates

Amyloid fibrils occur inside the human body, associated with ageing or a group of diseases that includes, amongst others, Alzheimer’s disease, atherosclerosis and type II diabetes. Many natural polypeptide chains are able to form amyloid fibrils in vivo or in vitro, and this ability has been suggested to represent an inherent consequence of the chemical structure of the polypeptide chain. Recent literature has provided a wealth of information about the structure of aggregates, precipitates, amyloid fibrils and other types of fibrillar polypeptide assemblies. However, the biophysical meaning associated with these terms can differ considerably depending on the context of their usage. This overview presents a structural comparison of amyloid fibrils and other types of polypeptide assemblies and defines amyloid fibrils, based on structural considerations, as fibrillar polypeptide aggregates with a cross-β conformation. Received 1 March 2007; received after revision 15 March 2007; accepted 25 April 2007     

Hyaluronan synthases: fascinating glycosyltransferases from vertebrates, bacterial pathogens, and algal viruses

Hyaluronan (or hyaluronic acid or hyaluronate; HA) is a polysaccharide found in the extracellular matrix of vertebrate tissues and in the surface coating of certain Streptococcus and Pasteurella bacterial pathogens. At least one algal virus directs its host to produce HA on the cell surface early in infection. HA synthases (HASs) are the enzymes that polymerize HA using uridine diphospho-sugar precursors. In all known cases, HA is secreted out of the cell; therefore, HASs are normally found in the outer membranes of the organism. In the last 6 years, the HASs have been molecularly cloned from all the above sources. They were the first class of glycosyltransferases identified in which a single polypeptide species catalyzes the transfer of two different monosaccharides; this finding is in contrast to the usual 'single enzyme, single sugar' dogma of glycobiology. There appear to be two distinct classes of HASs based on differences in amino acid sequence, topology in the membrane, and reaction mechanism. This review discusses the current state of knowledge surrounding the molecular details of HA biosynthesis and summarizes the possible evolutionary history of the HASs.     

Occurrence of 3-methoxy octadecanoic acid in yeast lipid

Summary The fatty acid composition of a new strain of the yeastRhodotorula glutinis, grown in molasses, has been studied and found to contain palmitic, stearic, oleic, linoleic and linolenic acids, and small amounts of other constituents. In addition, 3-methoxy octadecanoic acid has been shown to be present in the glycolipid fraction.Partly presented at the National Symposium on Natural Product Chemistry held on February 7–8, 1983 at Bose Institute, Calcutta (India).Acknowledgments. Authors are indebted to Prof. S.C. Bhattacharyya, and Prof. A.K. Barua, Department of Chemistry for providing facilities for this work.     

The synthesis of total and specific glycosaminoglycans during development of experimental liver cirrhosis

Summary During hepatic fibrogenesis induced by long-term administration of thioacetamide, the synthsis of chondroitin 4,6-sulfate and hyaluronic acid was strongly enhanced; the formation of heparan sulfate comprising at least 70% of total liver GAG synthesis and of a keratan-sulfate-like fraction was stimulated 1.7fold. Formation of dermatan-sulfate in liver could not be detected.We are grateful to Prof. W. Kühnel, Department of Anatomy, and to Prof. R. Lindenfelser, Department of Pathology, RWTH Aachen, for critical examination of the histology.     

Physiological and pathological properties of α-synuclein

alpha-Synuclein belongs to a small group of natively unfolded proteins that can transiently bind to lipid membranes and acquire a partial alpha-helical conformation. Under certain pathogenic conditions, alpha-synuclein aggregates to form oligomers and insoluble fibrils with increased ss-sheet configuration. Although genetic mutations and multiplications of the gene have been found in familial cases, the mechanism by which this protein aggregates in sporadic cases of Parkinson's disease, dementia with Lewy bodies and multisystem atrophy is not fully understood. Here we review the function of alpha-synuclein and recent insight into the mechanisms by which it aggregates.     

Demonstration of retinoic acid isomers in human urine under physiological conditions

Summary Untransformed retinoic acid has never been demonstrated in human excreta under normal physiological conditions. We have developed a two-step liquid chromatographic system for the demonstration of subnanogram amounts of this compound in human urine without administration of any precursor.The work was supported by a grant of the N.F.S.R. to W.L.     

Lipid sensing and lipid sensors

The field of bile acids has witnessed an impulse in the last two decades. This has been the result of cloning the genes encoding enzymes of bile acid synthesis and their transporters. There is no doubt that the identification of Farnesoid X Receptor (FXR, NR1H4) as the bile acid receptor has contributed substantially to attract the interest of scientists in this area. When FXR was cloned by Forman et al. [1], farnesol metabolites were initially considered the physiological ligands. After identifying FXR and other nuclear receptors as bile acid sensors [2-4], it has become clear that bile acids are involved in the regulation of lipid and glucose metabolism and that these molecules are eclectic regulators of diverse cellular functions. In this review, we will summarize the current knowledge of the functions regulated by bile acids and how their physiological receptors mediate the signaling underlying numerous cellular responses.     

Stereospezifische Polymerisationen cyclischer Monomerer

Summary Cyclic monomers polymerizable stereospecifically can be divided into two classes: monomers in which the polymerizable double bond is situated outside the ring and those in which the polymerizable group is in the ring itself.For the first group it is shown how the ring and its substituents influence the rate, stereospecificity and the polymerization mechanism as well as the crystallizability and the crystalline structure of the tactic polymers formed.With regard to the 2nd group the possible polymerization mechanisms are indicated that can on the whole occur through cleavage of the ring or opening of the double bond, for numerous typical representatives of this class of monomers and the criteria are explained on which stereospecificity depends.     

Protein complexes in snake venom

Snake venom contains mixture of bioactive proteins and polypeptides. Most of these proteins and polypeptides exist as monomers, but some of them form complexes in the venom. These complexes exhibit much higher levels of pharmacological activity compared to individual components and play an important role in pathophysiological effects during envenomation. They are formed through covalent and/or non-covalent interactions. The subunits of the complexes are either identical (homodimers) or dissimilar (heterodimers; in some cases subunits belong to different families of proteins). The formation of complexes, at times, eliminates the non-specific binding and enhances the binding to the target molecule. On several occasions, it also leads to recognition of new targets as protein-protein interaction in complexes exposes the critical amino acid residues buried in the monomers. Here, we describe the structure and function of various protein complexes of snake venoms and their role in snake venom toxicity.     

Mobile genetic elements of Staphylococcus aureus

Bacteria such as Staphylococcus aureus are successful as commensal organisms or pathogens in part because they adapt rapidly to selective pressures imparted by the human host. Mobile genetic elements (MGEs) play a central role in this adaptation process and are a means to transfer genetic information (DNA) among and within bacterial species. Importantly, MGEs encode putative virulence factors and molecules that confer resistance to antibiotics, including the gene that confers resistance to beta-lactam antibiotics in methicillin-resistant S. aureus (MRSA). Inasmuch as MRSA infections are a significant problem worldwide and continue to emerge in epidemic waves, there has been significant effort to improve diagnostic assays and to develop new antimicrobial agents for treatment of disease. Our understanding of S. aureus MGEs and the molecules they encode has played an important role toward these ends and has provided detailed insight into the evolution of antimicrobial resistance mechanisms and virulence.     

Absolute configuration of (+)-1,4-diphenyl-2,3-butanediol

Summary The absolute configuration of the title compound, isolated earlier from bull testicular tissue, has been determined to be (2S,3S) by synthesis of the natural diol from L-(+)-tartaric acid.Acknowledgment. This research was supported by a research grant (GM-28236) from the National Institutes of Health, to whom the authors express their appreciation.