ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916099

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

A survey of 124 protein and/or nucleic acid chemistry facilities has provided a basis for estimating the resources needed to establish a facility, the financial support needed to keep it operating, and the technical capabilities it might reasonably be expected to achieve. Based on these data, an average core facility occupied 870 ft2, was staffed by three full‐time personnel, and was equipped with 4‐5 major instrument systems. Because user fees generated an average of about $101,000/year in income compared with an average operating budget of about $197,000/year, even a facility that charged user fees would, on average, still require an annual subsidy of about $96,000. Although most government and industrial core facilities did not assess user fees, at least 83 of the 124 respondents did have a preestablished schedule of service charges that enabled a compilation to be made of the average cost of providing a number of typical facility analyses and syntheses. The greater than 100‐fold range in charges assessed in core facilities for seemingly identical services was shown to result from the equally large range in the degree of subsidization of these laboratories. Although an average facility might be expected to offer four or five of the following six major services — amino acid sequencing, amino acid analysis, HPLC peptide isolation, peptide synthesis, fragmentation of proteins and DNA synthesis — less than 10% of the responding laboratories provided mass spectrometry, capillary zone electrophoresis, or RNA synthesis. With the exception of peptide synthesis, which had an average turn‐around time of about 24 days, all other major services had turn‐around times that averaged in the range of 4–9 days. Additional data are summarized regarding average sample throughput in core laboratories and the amount of protein that is needed for hydrolysis/amino acid analysis and sequencing.—Niece, R. L.; Beach, C. M.; Cook, R. F.; Hathaway, G. M.; Williams, K. R. State‐of‐the‐art biomolecular core facilities: a comprehensive survey.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916100

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Evidence indicates that principal features of the membrane involve structural organization of lipids in the form of a bilayer with functional proteins either bound to the bilayer surface or inserted into the bilayer and interacting within specific domains in the lipid milieux. In homeotherms, intrinsic and extrinsic factors apparently form the basis for determination of membrane lipid composition and thus membrane physicochemical properties. Moreover, many intrinsic metabolic controls, such as fatty acid desaturation and phospholipid biosynthesis, may be attenuated by change in the nature of the extrinsic or dietary influence. This review will focus on the role of dietary fat as a determinant of subcellular structural constituents to illustrate that feeding nutritionally adequate diets differing in fatty acid composition can induce physiological transitions in membrane function involving the activity of enzymes responsible for synthesis of membrane constituents, hormone‐activated functions and expression of activity in the cell nucleus.—Clandinin, M. T.; Cheema, S.; Field, C. J., Garg, M. L., Venkatraman, J., Clandinin, T. R. Dietary fat: exogenous determination of membrane structure and cell function.FASEB J.5: 2761‐2769; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916101

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Small, resting B lymphocytes are driven into the cell cycle as a consequence of receiving multiple signals from elements found within their local environment. The first of these signals results from the binding of specific antigen to membrane immunoglobulin (mIg) receptors on the B cells. Pursuant to antigen binding, signals are transduced and the B cell commences to endocytose and degrade the antigen. Fragments of the antigen are expressed on the B cell surface in noncovalent association with class II major histocompatibility complex (MHC) molecules. The antigen‐class II MHC complex serves as a recognition complex for CD4+helper T cells (Th). As a consequence of recognition, Thform stable physical conjugates with the B cells. Over an extended period of time the Thand B cells bilaterally signal one another. This interchange of signals results in the growth and differentiation of both cells. This review will discuss the sequence of events that culminate in the growth and differentiation of B lymphocytes to antibody‐producing cells.—Noelle, R. J.; Snow, E. C. T helper cell‐dependent B cell activation.FASEB J.5: 2770‐2776; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1833257

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

In acquired tolerance, previous exposure to antigen under certain conditions induces specific unresponsiveness instead of specific immunological memory. It has been studied as an approach to the mechanisms of self‐tolerance that operate on immunocompetent T and B lymphocytes once they leave their sites of origin in the thymus and the bone marrow. Possible mechanisms involve induction of specific suppressor cells or inactivation of antigen‐specific lymphocytes (clonal anergy) as a consequence of abortive antigen presentation, in which the antigen receptor is effectively engaged but certain poorly defined accessory signals the T lymphocytes require are lacking. We propose that small, resting B lymphocytes, which lack these accessory signals, are the inactivating antigen‐presenting cells in acquired tolerance to proteins and to the class II transplantation antigens. B lymphocytes, which can use their antigen receptors to gather and process antigens that are present at very low concentrations, may play a role in self‐tolerance. In addition, B lymphocytes and T lymphocytes rendered anergic by encounter with self antigens could persist as self‐specific suppressor cells to block an autoimmune response of autoreactive clones that had escaped deletion or anergy.—Parker, D. C.,; Eynon, E. E. Antigen presentation in acquired immunological tolerance.FASEB J.5: 2777‐2784; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916102

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Guanylyl cyclases, which catalyze the formation of the intracellular signal molecule cyclic GMP from GTP, display structural features similar to other signal‐transducing enzymes such as protein tyrosine‐kinases and protein tyrosine‐phosphatases. So far, three isoforms of mammalian membrane‐bound guanylyl cyclases (GC‐A, GC‐B, GC‐C), which are stimulated by either natriuretic peptides (GC‐A, GC‐B) or by the enterotoxin ofEscherichia coli(GC‐C), have been identified. These proteins belong to the group of receptor‐linked enzymes, with different NH2‐terminal extracellular receptor domains coupled to a common intracellular catalytic domain. In contrast to the membrane‐bound enzymes, the heme‐containing soluble guanylyl cyclase is stimulated by NO and NO‐containing compounds and consists of two subunits (α1andβ1). Both subunits contain the putative catalytic domain, which is conserved in the membrane‐bound guanylyl cyclases and is found twice in adenylyl cyclases. Coexpression of theα1‐ andβ1‐subunit is required to yield a catalytically active enzyme. Recently, another subunit of soluble guanylyl cyclase was identified and designatedβ2, revealing heterogeneity among the subunits of soluble guanylyl cyclase. Thus, different enzyme subunits may be expressed in a tissue‐specific manner, leading to the assembly of various heterodimeric enzyme forms. The implications concerning the physiological regulation of soluble guanylyl cyclase are not known, but different mechanisms of soluble enzyme activation may be due to heterogeneity among the subunits of soluble guanylyl cyclase.—Koesling, D.; Böhme, E.; Schultz, G. Guanylyl cyclases, a growing family of signal‐transducing enzymes.FASEB J.5: 2785‐2791; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1680765

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The first step in the biosynthesis of secretory proteins, plasma membrane proteins, and many other proteins in a eukaryotic cell involves the transport of at least portions of the polypeptides across the endoplasmic reticulum (ER) membrane. Parts of the polypeptide chains serve as signals that direct the translocation across and the integration into the ER membrane and also determine the orientation of membrane proteins. The transport process itself may be divided into two phases: an initiation or targeting cycle, which is fairly well understood, and the actual transfer of the polypeptide chain through the membrane, the mechanism of which is still mysterious. The initiation cycle generally involves the function of the signal recognition particle (SRP) which binds to signal sequences through its 54‐kDa polypeptide component, and of the SRP‐receptor (docking protein) in the ER membrane whose function is dependent on GTP. The membrane transfer of the polypeptide chain appears to involve a translocation complex consisting of several membrane proteins, one of which is the signal sequence receptor protein (SSR).—Rapoport, T. A. Protein transport across the endoplasmic reticulum membrane: facts, models, mysteries.FASEB J.5: 2792‐2798; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916103

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Neurodegenerative diseases of animals and humans including scrapie, bovine spongiform encephalopathy, and Creutzfeldt‐Jakob disease are caused by unusual infectious pathogens called prions. There is no evidence for a nucleic acid in the prion, but diverse experimental results indicate that a host‐derived protein called PrPScis a component of the infectious particle. Experiments with scrapie‐infected cultured cells show that PrPScis derived from a normal cellular protein called PrPCthrough an unknown posttranslational process. We have analyzed the amino acid sequence and posttranslational modifications of PrPScand its proteolytically truncated core PrP 27‐30 to identify potential candidate modifications that could distinguish PrPScfrom PrPC. The amino acid sequence of PrP 27‐30 corresponds to that predicted from the gene and cDNA. Mass spectrometry of peptides derived from PrPSchas revealed numerous modifications including two N‐linked carbohydrate moieties, removal of an amino‐terminal signal sequence, and alternative COOH termini. Most molecules contain a glycosylinositol phospholipid (GPI) attached at Ser‐231 that results in removal of 23 amino acids from the COOH terminus, whereas 15% of the protein molecules are truncated to end at Gly‐228. The structure of the GPI from PrPSchas been analyzed and found to be novel, including the presence of sialic acid. Other experiments suggest that the N‐linked oligosaccharides are not necessary for PrPScformation. Although detailed comparison of PrPScwith PrPCis required, there is no obvious way in which any of the modifications might confer upon prpScits unusual physical properties and allow it to act as a component of the prion. If no chemical difference is found between PrPCand PrPSc, then the two isoforms of the prion protein may differ only in their conformations or by the presence of bound cellular components.—Stahl, N.; Prusiner, S. B. Prions and prion proteins.FASEB J.5: 2799‐2807; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916104

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Contrary to earlier beliefs, viruses are not the smallest causative agents of infectious diseases. Single‐stranded RNAs as small as 246 nucleotides exist in certain higher plants and cause more than a dozen crop diseases. These RNAs have been termed viroids. Despite their extremely limited information content, viroids replicate autonomously in susceptible cells — that is, they do not require helper functions from simultaneously replicating conventional viruses. Viroids are covalently closed circular molecules with a characteristic rodlike secondary structure in which short helical regions are interrupted by internal and bulge loops. Viroids are not translated; they are replicated by a host enzyme (or enzymes) (probably RNA polymerase II) via oligomeric RNA intermediates by a rolling circle mechanism. Viroidlike satellite RNAs resemble viroids in size and molecular structure, but are found within the capsids of specific helper viruses on which they depend for their own replication. These RNAs are of great interest to molecular biology for at least two reasons: 1) they are the smallest and simplest replicating molecules known, and2) they may represent living fossils of precellular evolution in a hypothetical RNA world.—Diener, T. O. Subviral pathogens of plants: viroids and viroidlike satellite RNAs.FASEB J.5: 2808‐2813; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1717335

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Collagen molecules are structural macromolecules of the extracellular matrix that include in their structure one or several domains that have a characteristic triple helical conformation. They have been classified by types that define distinct sets of polypeptide chains that can form homo‐ and heterotrimeric assemblies. All the collagen molecules participate in supramolecular aggregates that are stabilized in part by interactions between triple helical domains. Fourteen collagen types have been defined so far. They form a wide range of structures. Most notable are1) fibrils that are found in most connective tissues and are made by alloys of fibrillar collagens (types I, II, III, V, and XI) and2) sheets constituting basement membranes (type IV collagen), Descemet's membrane (type VIII collagen), worm cuticle, and organic exoskeleton of sponges. Other collagens, present in smaller quantities in tissues, play the role of connecting elements between these major structures and other tissue components. The fibril‐associated collagens with interrupted triple helices (FACITs) (types IX, XII, and XIV) appear to connect fibrils to other matrix elements. Type VII collagen assemble into anchoring fibrils that bind epithelial basement membranes and entrap collagen fibrils from the underlying stroma to glue the two structures together. Type VI collagen forms thin‐beaded filaments that may interact with fibrils and cells.—van der Rest, M.; Garrone, R. Collagen family of proteins.FASEB J.5: 2814‐2823; 1991.

ISSN:0892-6638    

DOI:10.1096/fasebj.5.13.1916105

出版商:Wiley    

年代:1991

数据来源: WILEY