scholarly journals Functional dissection of the CD21/CD19/TAPA-1/Leu-13 complex of B lymphocytes.

1993 ◽  
Vol 178 (4) ◽  
pp. 1407-1417 ◽  
Author(s):  
A K Matsumoto ◽  
D R Martin ◽  
R H Carter ◽  
L B Klickstein ◽  
J M Ahearn ◽  
...  
Keyword(s):  
B Lymphocytes ◽  
Protein Complexes ◽  
Pi3 Kinase ◽  
Free Calcium ◽  
Wild Type ◽  
Extracellular Domains ◽  
Membrane Immunoglobulin ◽  
Low Concentrations ◽  
Cellular Aggregation ◽  
Membrane Protein Complexes

The CD21/CD19/TAPA-1 complex of B lymphocytes amplifies signal transduction through membrane immunoglobulin (mIg), recruits phosphatidylinositol 3-kinase (PI3-kinase), and induces homotypic cellular aggregation. The complex is unique among known membrane protein complexes of the immune system because its components represent different protein families, and can be expressed individually. By constructing chimeric molecules replacing the extracellular, transmembrane, and cytoplasmic regions of CD19 and CD21 with those of HLA-A2 and CD4, we have determined that CD19 and TAPA-1 interact through their extracellular domains, CD19 and CD21 through their extracellular and transmembrane domains, and, in a separate complex, CD21 and CD35 through their extracellular domains. A chimeric form of CD19 that does not interact with CD21 or TAPA-1 was expressed in Daudi B lymphoblastoid cells and was shown to replicate two functions of wild-type CD19 contained within the complex: synergistic interaction with mIgM to increase intracellular free calcium and tyrosine phosphorylation and association with the p85 subunit of PI3-kinase after ligation of mIgM. The chimeric CD19 lacked the capacity of the wild-type CD19 to induce homotypic cellular aggregation, a function of the complex that can be ascribed to the TAPA-1 component. The CD21/CD19/TAPA-1 complex brings together independently functioning subunits to enable the B cell to respond to low concentrations of antigen.

scholarly journals Molecular interactions of complement receptors on B lymphocytes: a CR1/CR2 complex distinct from the CR2/CD19 complex.

1991 ◽  
Vol 173 (5) ◽  
pp. 1083-1089 ◽  
Author(s):  
D A Tuveson ◽  
J M Ahearn ◽  
A K Matsumoto ◽  
D T Fearon
Keyword(s):  
B Cell ◽  
B Lymphocytes ◽  
Cell Activation ◽  
Complement Receptors ◽  
B Cell Activation ◽  
Humoral Immune ◽  
Membrane Immunoglobulin ◽  
Erythroleukemia Cells ◽  
Low Concentrations ◽  
The Complement System

The complement system augments the humoral immune response to low concentrations of antigen. This effect may be partly mediated by complement receptors on the surface of B lymphocytes that bind immunogenic complexes bearing fragments of C3 and C4. We have shown by immunoprecipitation analysis that the two complement receptors expressed by B lymphocytes, complement receptor 1 (CR1) and CR2, form a detergent-sensitive complex on the surface of tonsillar B lymphocytes and on K562 erythroleukemia cells that were co-transfected with cDNAs encoding CR1 and CR2. The CR1/CR2 complex is distinct from the CR2/CD19 complex and may assist B cell activation by efficiently capturing C3b-containing immunogens and maintaining such immunogens on the B cell after CR1 and factor I-mediated cleavage to iC3b and C3dg. The complement activating immunogen may then trigger signal transduction by the CR1/CR2 complex, the CR2/CD19 complex, or membrane immunoglobulin.

scholarly journals An intragenic suppressor of a calmodulin mutation in Paramecium: genetic and biochemical characterization.

Genetics ◽  
1991 ◽  
Vol 129 (3) ◽  
pp. 717-725
Author(s):  
R D Hinrichsen ◽  
M Pollock ◽  
T Hennessey ◽  
C Russell
Keyword(s):  
Calcium Binding ◽  
Biochemical Characterization ◽  
Behavioral Responses ◽  
Free Calcium ◽  
Paramecium Tetraurelia ◽  
Wild Type ◽  
Low Concentrations ◽  
K Current ◽  
Increased Sensitivity ◽  
Intragenic Suppressor

Abstract We describe a suppressor of the calmodulin mutant cam1 in Paramecium tetraurelia. The cam1 mutant, which has a SER----PHE change at residue 101 of the third calcium-binding domain, inhibits the activity of the Ca(2+)-dependent K+ current and causes exaggerated behavioral responses to most stimuli. An enrichment scheme, based on an increased sensitivity to Ba2+ in cam1 cells, was used to isolate suppressors. One such suppressor, designated cam101, restores both the activity of the Ca(2+)-dependent K+ current and behavioral responses of the cells. We show that the cam101 mutant is an intragenic suppressor of cam1, based on genetic and microinjection data. The cam101 calmodulin is shown to be similar to wild-type calmodulin in terms of its ability to stimulate calmodulin-dependent phosphodiesterase at low concentrations of free calcium. However, the cam101 calmodulin has a reduced affinity for a monoclonal antibody to wild-type Paramecium calmodulin, as does the parental cam1 calmodulin, and a different mobility on acid-urea gels relative to both wild-type and cam1 calmodulin. We have been able to demonstrate that the isolation of intragenic suppressors of a calmodulin mutation is possible, which allows for the further genetic analysis of structure-function relationships in the calmodulin molecule.

scholarly journals Intracellular targeting of antigens internalized by membrane immunoglobulin in B lymphocytes.

1995 ◽  
Vol 181 (5) ◽  
pp. 1705-1714 ◽  
Author(s):  
R N Mitchell ◽  
K A Barnes ◽  
S A Grupp ◽  
M Sanchez ◽  
Z Misulovin ◽  
...  
Keyword(s):  
B Lymphocytes ◽  
Class Ii ◽  
General Mechanism ◽  
Functional Assay ◽  
Antigenic Peptides ◽  
Wild Type ◽  
Intracellular Targeting ◽  
Intracellular Processing ◽  
Membrane Immunoglobulin ◽  
Antigen Presenting

An important function of membrane immunoglobulin (mIg), the B cell antigen receptor, is to endocytose limiting quantities of antigen for efficient presentation to class II-restricted T cells. We have used a panel of mIg mutants to analyze the mechanism of mIg-mediated antigen presentation, and specifically to explore the ability of mIg to target internalized antigen to intracellular processing compartments. Transfected mIgs carrying substitutions for the transmembrane Tyr587 residue fail to efficiently present specifically bound antigen. However, these mutants internalize antigen normally, and their defect cannot be attributed to a lack of mIg-associated Ig alpha/Ig beta molecules. A novel functional assay for detecting antigenic peptides in subcellular fractions shows that wild-type mIg transfectants generate class II-peptide complexes intracellularly, whereas only free antigenic peptides are detectable in the mutant mIg transfectants. Furthermore, an antigen competition assay reveals that antigen internalized by the mutant mIgs fails to enter the intracellular processing compartment accessed by wild-type mIg. Therefore, mIg specifically targets bound and endocytosed antigen to the intracellular compartment where processed peptides associate with class II molecules, and the transmembrane Tyr587 residue plays an obligatory role in this process. Targeting of internalized antigen may be mediated by receptor-associated chaperones, and may be a general mechanism for optimizing the presentation of specifically bound and endocytosed antigens in b lymphocytes and other antigen-presenting cells.

Increased Aggregation and Secretion Responses of Human Platelets when Loaded with the Calcium Fluorescent Probes Quin2 and Fura-2

1987 ◽  
Vol 58 (02) ◽  
pp. 737-743 ◽  
Author(s):  
Frarnçois Lanza ◽  
Alain Beretz ◽  
Martial Kubina ◽  
Jean-Pierre Cazenave
Keyword(s):  
Intracellular Calcium ◽  
Shape Change ◽  
Calcium Ionophore ◽  
Human Platelets ◽  
Arachidonic Acid Metabolism ◽  
Free Calcium ◽  
Membrane Bilayer ◽  
Fluorescent Indicators ◽  
Fura 2 ◽  
Low Concentrations

SummaryIncorporation into human platelets of the calcium fluorescent indicators quin2 or fura-2 at low concentrations used to measure intracellular free calcium leads to the potentiation of the effects of agonists on platelets. This was shown by increased aggregatory and secretory responses of quin2 or fura-2 loaded platelets after stimulation with ADP, PAP and with low concentrations of thrombin, collagen, the endoperoxide analog U-46619 and the calcium ionophore A 23187. Quin2 and fura-2 mediated platelet sensitisation could be due to altered arachidonic acid metabolism since it was inhibited by prior treatment with the cydooxygenase inhibitor acetylsalicylate. In contrast, platelets loaded with higher concentrations of calcium chelators exhibited diminished aggregation responses to all aggregating agents. This latter effect was accompanied by increased fluidity of the platelet plasma membrane bilayer and by the exposure of a new pool of membranes to the outer surface of platelets, as monitored with trimethylammonium- diphenylhexatriene (TMA-DPH) in platelets loaded with the non-fluorescent calcium probe analog MAPT. In contrast, low concentrations of quin2 did not potentiate shape change of platelets activated with ADP. Thus, shape change and aggregation can be influenced separately by intracellular Ca2+ chelators. We conclude that platelet responses are altered by the incorporation of intracellular calcium chelators at concentrations used to monitor intracellular calcium changes.

Conformational Flexibility in Assembly of Photosynthetic Membrane Protein Complexes in vivo

2004 ◽  
Vol 10 (S02) ◽  
pp. 1496-1497
Author(s):  
P A Bullough
Keyword(s):  
Membrane Protein ◽  
Protein Complexes ◽  
Conformational Flexibility ◽  
Photosynthetic Membrane ◽  
Membrane Protein Complexes

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Three-dimensional crystallization of membrane proteins

1988 ◽  
Vol 21 (4) ◽  
pp. 429-477 ◽  
Author(s):  
W. Kühlbrandt
Keyword(s):  
High Resolution ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Protein Complexes ◽  
Three Dimensional ◽  
Biological Macromolecules ◽  
X Ray ◽  
X Ray Crystallography ◽  
Membrane Protein Complexes ◽  
Essential Prerequisite

As recently as 10 years ago, the prospect of solving the structure of any membrane protein by X-ray crystallography seemed remote. Since then, the threedimensional (3-D) structures of two membrane protein complexes, the bacterial photosynthetic reaction centres of Rhodopseudomonas viridis (Deisenhofer et al. 1984, 1985) and of Rhodobacter sphaeroides (Allen et al. 1986, 1987 a, 6; Chang et al. 1986) have been determined at high resolution. This astonishing progress would not have been possible without the pioneering work of Michel and Garavito who first succeeded in growing 3-D crystals of the membrane proteins bacteriorhodopsin (Michel & Oesterhelt, 1980) and matrix porin (Garavito & Rosenbusch, 1980). X-ray crystallography is still the only routine method for determining the 3-D structures of biological macromolecules at high resolution and well-ordered 3-D crystals of sufficient size are the essential prerequisite.

scholarly journals The Synechococcus Strain PCC 7942glnN Product (Glutamine Synthetase III) Helps Recovery from Prolonged Nitrogen Chlorosis

2000 ◽  
Vol 182 (19) ◽  
pp. 5615-5619 ◽  
Author(s):  
Jörg Sauer ◽  
Ulrike Dirmeier ◽  
Karl Forchhammer
Keyword(s):  
Glutamine Synthetase ◽  
Transcriptional Start Site ◽  
Binding Motif ◽  
Class Iii ◽  
Wild Type ◽  
Cloning And Sequencing ◽  
Gene Encoding ◽  
Low Concentrations ◽  
Synechococcus Strain ◽  
Pcc 7942

ABSTRACT We report the cloning and sequencing of the glnN gene encoding a class III glutamine synthetase from the cyanobacteriumSynechococcus strain PCC 7942. Mapping of the transcriptional start site revealed a DNA sequence in the promoter region that resembles an imperfect NtcA binding motif. Expression ofglnN is impaired in NtcA- and PII-deficient mutants. The only parameter which was negatively affected in theglnN mutant compared to the wild type was the recovery rate of prolonged nitrogen-starved cells with low concentrations of combined nitrogen.

Sign in / Sign up

Export Citation Format

Share Document