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F Hochstenbach

Publications and source records attributed to F Hochstenbach.

15 recordsLinked to original sources
PubMed1998

Identification of a putative alpha-glucan synthase essential for cell wall construction and morphogenesis in fission yeast.

The cell wall protects fungi against lysis and determines their cell shape. Alpha-glucan is a major carbohydrate component of the fungal cell wall, but its function is unknown and its synthase has remained elusive. Here, we describe a fission yeast gene, ags1(+), which encodes a putative alpha-glucan synthase. In contrast to the structure of other carbohydrate polymer synthases, the predicted Ags1 protein consists of two probable catalytic domains for alpha-glucan assembly, namely an intracellular domain for alpha-glucan synthesis and an extracellular domain speculated to cross-link or remodel alpha-glucan. In addition, the predicted Ags1 protein contains a multipass transmembrane domain that might contribute to transport of alpha-glucan across the membrane. Loss of Ags1p function in a temperature-sensitive mutant results in cell lysis, whereas mutant cells grown at the semipermissive temperature contain decreased levels of cell wall alpha-glucan and fail to maintain rod shapes, causing rounding of the cells. These findings demonstrate that alpha-glucan is essential for fission yeast morphogenesis.

Amino Acid Sequence↗
PubMed1993

Interaction with newly synthesized and retained proteins in the endoplasmic reticulum suggests a chaperone function for human integral membrane protein IP90 (calnexin).

A cDNA clone encoding the human endoplasmic reticulum (ER) resident protein IP90 was isolated and sequenced. It predicts a transmembrane protein with a large ER luminal region showing sequence similarity to calreticulin and a short cytoplasmic domain containing a COOH-terminal RKPRRE sequence that may be relevant to its retention in the ER. It is 95% homologous to the canine ER membrane phosphorprotein called pp90 or calnexin (Wada, I., Rindress, D., Cameron, P. H., Ou, W.-J., Doherty, J. J., II, Louvard, D., Bell, A. W., Dignard, D., Thomas, D. Y., and Bergeron, J. J. M. (1991) J. Biol. Chem. 266, 19599-19610). Previously, in lymphocytes, we have characterized IP90 as a protein associated with partially assembled multichain proteins including the T cell receptor, the membrane immunoglobulin, and the heavy chain of the major histocompatibility complex class I molecules (Hochstenbach, F., David, V., Watkins, S., and Brenner, M. B. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 4734-4738). Here, we show that within a short metabolic labeling period, IP90 associates transiently with many different newly synthesized proteins. However, in a T cell line that cannot assemble a complete T cell receptor because it lacks the alpha subunit, the unassembled T cell receptor beta chains, which are retained in the ER, remain associated with IP90 throughout a prolonged chase time period. Together, these data offer further evidence suggesting that IP90 may act in assisting protein assembly and/or in the retention within the ER of unassembled protein subunits.

Amino Acid Sequence↗
PubMed1992

Endoplasmic reticulum resident protein of 90 kilodaltons associates with the T- and B-cell antigen receptors and major histocompatibility complex antigens during their assembly.

In the endoplasmic reticulum (ER), newly synthesized subunits of the T-cell antigen receptor (TCR), membrane-bound immunoglobulin (mIg), and major histocompatibility complex (MHC) class I antigens must fold correctly and assemble completely into multimeric protein complexes prior to transport to the cell surface. Although folding and assembly may occur spontaneously, the concept that molecular chaperones facilitate these events is emerging. Here, an intracellular protein of 90-kDa apparent molecular mass, denoted IP90, was shown to be an ER resident protein that associated with partial complexes of the TCR, mIg, and MHC class I proteins but was absent from fully assembled complexes. We speculate that IP90 might participate in folding and assembly processes of these and other multisubunit protein complexes during their transit through the ER.

Animals↗
PubMed1992

Quaternary structure and assembly process of the T cell receptor.

The human immune system contains T and B lymphocytes which respond in an antigen-specific manner to foreign antigens. These foreign antigens are recognized by multimeric receptors expressed on the cell surface of T and B lymphocytes. The subunits that make up the T and B cell receptor complexes have been identified, but their stoichiometries and positions in the complex remain to be resolved. Elucidation of the quaternary structures is necessary to understand the molecular basis of signal transduction events which follow antigen recognition and will contribute to the design of drugs that can modulate T and B cell responses. Here, I will discuss recent insights into the quaternary structures of the TCR and BCR and the striking similarities between the two, both in the structures of the subunits and in the overall quaternary structures. In addition, the intracellular assembly processes of these receptor complexes will be discussed, as well as the recent realization that these processes appear to be mediated by house-keeping proteins that transiently bind to partial TCR and BCR complexes. Similar to the role of BiP which mediates assembly processes of B cell immunoglobulins, a recently identified intracellular protein of 90 kD, called IP90, appears to play a role in TCR and BCR assembly processes. Analyses of the IP90 protein might contribute not only insight into the folding and assembly processes in lymphocytes, but also into those of newly synthesized proteins in many different cell types.

Base Sequence↗
PubMed1990

Characterization of a maternal type VI collagen in Xenopus embryos suggests a role for collagen in gastrulation.

We characterized a novel extracellular matrix element that is present in the earliest developmental stages of Xenopus laevis, and is recognized by an mAb 3D7. Based on amino acid composition, breakdown patterns by bacterial collagenases, and the molecular weights of the components of the antigen (240, 200, and 140 kD), we found it very similar to mammalian collagen type VI. The antigen is evenly distributed in unfertilized eggs. Shortly after fertilization, it becomes localized intracellularly in the periphery of the cleaving embryo as well as in the extracellular spaces. During gastrulation, the antigen was localized in the cells lining the blastopore and in the extracellular space between the two cell layers, in the presumptive archenteron. When Fab elements of the 3D7 antibody were added to the culture medium, gastrulation was blocked, suggesting a role for the antigen in gastrulation movements.

Amino Acids↗
PubMed1989

T-cell receptor delta-chain can substitute for alpha to form a beta delta heterodimer.

Specific monoclonal antibodies have made possible the identification of two T-cell antigen receptor (TCR) heterodimers, alpha beta TCR and gamma delta TCR. Formation of these receptors is largely separated by the preferential pairing of alpha-TCR with beta and gamma-TCR with delta, the sequential rearrangement and expression of the TCR loci during thymic development and the deletion of the delta-loci either prior to or concomitant with alpha-rearrangement in alpha beta TCR cells. Here we show that delta-TCR can substitute for alpha in pairing with beta to form a beta delta heterodimer. This receptor is expressed on the cell surface of the T-leukaemia cell line DND41 as analysed with beta- and delta-specific monoclonal antibodies. We suggest that a variety of factors including, for example, the deletion of the delta-TCR loci, can now be understood as exclusion mechanisms operating to prevent not only the formation of gamma delta receptors, but also of beta delta T-cell receptors, thereby promoting the numerically dominant alpha beta TCR lineage. Nevertheless, some developing T-cells that do not rearrange the alpha-loci may express the beta delta TCR as described here.

Animals↗
PubMed1989

Expression of human T cell receptor-gamma delta structural forms.

The human TCR-gamma delta occurs in three biochemically distinct forms (forms 1, 2bc, and 2abc). A 40-kDa TCR gamma-chain is disulfide-linked to the TCR delta-chain in form 1, whereas 40-kDa or 55-kDa TCR-gamma polypeptides are noncovalently associated with the TCR delta-chain in forms 2bc and 2abc, respectively. Sequence analysis of TCR-gamma cDNA clones indicates that form 1 utilizes the C gamma 1 gene segment, whereas forms 2bc and 2abc appear to use allelic C gamma 2 gene segments containing either two copies (b and c) or three copies (a, b, and c) of the CII exon, respectively. We transfected TCR-gamma cDNA encoding form 1 or form 2abc into the MOLT-13 cell line that expresses form 2bc. The transfected TCR gamma-chains associate with the resident MOLT-13 TCR-delta, normally part of form 2bc, to yield CD3-associated TCR-gamma delta heterodimers identical to those seen on the donor cell lines (form 1 or 2abc). These transfection experiments show directly that, 1) when a single TCR-delta subunit is available, the presence or absence of disulfide linkage between TCR gamma- and TCR delta-chains is controlled by the TCR gamma-chain, and 2) the difference in the amount of N-linked carbohydrate attached to the transfected TCR-gamma proteins of form 2bc vs form 2abc is influenced by the presence or absence of CII exon copy "a" which appears to alter the secondary and/or tertiary structure of these TCR gamma-chain constant regions, thereby affecting the attachment of N-linked glycans. In contrast to the similar structure and usage of C beta 1 and C beta 2, TCR-gamma delta forms show striking differences in structure and are not equally represented in peripheral blood. Although the role of each form is unknown, it is possible that variable or joining-gene segment selection events or functional differences account for their unequal usage.

Cell Line↗
PubMed1989

Double-negative (CD4-CD8-) lymphocytes bearing T-cell receptor alpha and beta chains in normal human skin.

Double-negative (CD4-CD8-) T-cell receptor alpha- and beta-chain (TCR alpha beta)-expressing lymphocytes have been identified in human skin. Two skin-derived lymphocyte cell lines (II-1 and II-2) expressing this phenotype were obtained. They each expressed full-length TCR alpha- and beta-chain transcripts and lacked TCR gamma- and delta-chain as well as CD4 and CD8 mRNAs. These polyclonal cell lines shared one predominant TCR beta-chain gene rearrangement. The CD3/TCR alpha beta complexes were functionally competent as evidenced by their capacity to transduce activation signals resulting in cell proliferation, lymphokine secretion, and cytolytic activity. The demonstration of CD4-CD8-TCR alpha beta lymphocytes as a subpopulation of the skin-associated immune system should contribute to understanding the biologic potential of this cell population as well as of this organ-specific immune system.

Adult↗
PubMed1988

Surface expression of only gamma delta and/or alpha beta T cell receptor heterodimers by cells with four (alpha, beta, gamma, delta) functional receptor chains.

Surface expression of TCR dimers by cells synthesizing three or four distinct types of receptor chains was analyzed. Cells containing intact gamma, alpha, and beta chains had only gamma delta dimers on the cell surface. In human PEER cells, addition of a functional alpha chain led to the loss of gamma delta dimer expression and expression of only alpha beta dimers. This result was not due to transcriptional down-regulation of the gamma or delta loci. In murine cells expressing all four chains, both gamma delta and alpha beta dimers could be demonstrated on a single cell. No other chain combinations (alpha gamma, alpha delta, beta gamma, or beta delta) were detected. Thus, there is stringent control of assembly and/or transport of TCR heterodimers, such that functional receptors consist only of alpha beta and gamma delta pairs, and no additional repertoire diversity is generated by cross pairing.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1988

Characterization of a third form of the human T cell receptor gamma/delta.

A subpopulation of the CD3+ peripheral T lymphocytes express the TCR-gamma/delta complex. Three distinct TCR-gamma forms that differ in size and in the ability to form a disulfide bridge with the TCR-delta subunit have been described. In this study we analyze the structural difference between the non-disulfide-linked 55-kD and 40-kD TCR-gamma chains. The 40-kD TCR-gamma form contains a smaller polypeptide backbone and carries less carbohydrate compared with the 55-kD TCR-gamma form. A cDNA clone corresponding to the 40-kD TCR-gamma subunit lacks one copy of the second exon of the constant region that is present in the other TCR-gamma subunit. This exon copy encodes part of the connector region that is located between the constant domain and the membrane spanning region. We show that the number of potential N-linked glycan attachment sites are the same for the two TCR-gamma forms. Since these attachment sites are located in the connector region we conclude that the connector region influences the amount of N-linked carbohydrates added to the core TCR-gamma polypeptide, probably by affecting the conformation of the protein. In contrast to the TCR-beta constant region usage, the TCR-gamma constant regions are unequally expressed. Virtually exclusive usage of disulfide-linked complexes were found in some individuals, while both the disulfide-linked and the 40-kD, non-disulfide-linked TCR-gamma forms were detected in other subjects. The ability to distinguish these TCR-gamma/delta forms now makes it possible to study the mechanisms that govern their selection and to determine if they correspond to functionally distinct isotypes.

Amino Acid Sequence↗
PubMed1987

The human beta 2-microglobulin gene. Primary structure and definition of the transcriptional unit.

The human genomic clone pb2m13 contains a functional beta 2-microglobulin (B2m) gene, which upon transfection is readily expressed in murine fibroblasts. Here we report the nucleotide sequence of the human beta 2m gene and of a nearly full length cDNA clone. A comparison with the murine beta 2m gene reveals that exon/intron boundaries are absolutely conserved. In the protein-coding regions the similarity is 70%. As far as intron sequences of the murine beta 2m gene are available, no significant similarity between human and murine genes is observed. The transcriptional start site of the human beta 2m gene was determined by S1 mapping, and comparison with the nearly full length cDNA clone now defines the transcriptional unit of the beta 2m gene. In the 5' region of the gene strong clustering of the usually underrepresented CpG dinucleotide is found resembling a similar overrepresentation in the 5' regions of the major histocompatibility complex class I genes.

Amino Acid Sequence↗
PubMed1987

Immunochemical proof that a novel rearranging gene encodes the T cell receptor delta subunit.

The T cell receptor (TCR) delta protein is expressed as part of a heterodimer with TCR gamma, in association with the CD3 polypeptides on a subset of functional peripheral blood T lymphocytes, thymocytes, and certain leukemic T cell lines. A monoclonal antibody directed against TCR delta was produced that binds specifically to the surface of several TCR gamma delta cell lines and immunoprecipitates the TCR gamma delta as a heterodimer from Triton X-100 detergent lysates and also immunoprecipitates the TCR delta subunit alone after chain separation. A candidate human TCR delta complementary DNA clone (IDP2 O-240/38), reported in a companion paper, was isolated by the subtractive library approach from a TCR gamma delta cell line. This complementary DNA clone was used to direct the synthesis of a polypeptide that is specifically recognized by the monoclonal antibody to TCR delta. This complementary DNA clone thus corresponds to the gene that encodes the TCR delta subunit.

Antibodies, Monoclonal↗
PubMed1987

Crosses of two independently derived transgenic mice demonstrate functional complementation of the genes encoding heavy (HLA-B27) and light (beta 2-microglobulin) chains of HLA class I antigens.

In man a number of diseases are associated with certain alleles of MHC antigens. The most pronounced example is ankylosing spondylitis, which is strongly associated with HLA-B27. As a first step towards a model system to study the basis of this association, transgenic mice were generated that showed cell surface expression of the HLA-B27 antigen biochemically indistinguishable from HLA-B27 antigen expressed on human cells. This result was obtained by crossing two independently derived strains of mice, one of which is transgenic for the HLA-B27 heavy chain gene, and the other carrying and expressing the human beta 2m gene. Examination of HLA-B27 and human beta 2m mRNA in various tissues shows the two genes to be expressed in a coordinate fashion. The mRNA levels follow those of endogenous H-2 Class I genes.

Animals↗