scholarly journals Identification of a novel functional specificity signal within the GPI anchor signal sequence of carcinoembryonic antigen

2007 ◽  
Vol 177 (2) ◽  
pp. 211-218 ◽  
Author(s):  
Thomas B. Nicholson ◽  
Clifford P. Stanners
Keyword(s):  
Amino Acids ◽  
Carcinoembryonic Antigen ◽  
Cell Adhesion Molecule ◽  
Signal Sequence ◽  
Mature Protein ◽  
Functional Specificity ◽  
Gpi Anchor ◽  
Neural Cell Adhesion ◽  
Tumorigenic Activity ◽  
Necessary And Sufficient

Exchanging the glycophosphatidylinositol (GPI) anchor signal sequence of neural cell adhesion molecule (NCAM) for the signal sequence of carcinoembryonic antigen (CEA) generates a mature protein with NCAM external domains but CEA-like tumorigenic activity. We hypothesized that this resulted from the presence of a functional specificity signal within this sequence and generated CEA/NCAM chimeras to identify this signal. Replacing the residues (GLSAG) 6–10 amino acids downstream of the CEA anchor addition site with the corresponding NCAM residues resulted in GPI-anchored proteins lacking the CEA-like biological functions of integrin modulation and differentiation blockage. Transferring this region from CEA into NCAM in conjunction with the upstream proline (PGLSAG) was sufficient to specify the addition of the CEA anchor. Therefore, this study identifies a novel specificity signal consisting of six amino acids located within the GPI anchor attachment signal, which is necessary and sufficient to specify the addition of a particular functional GPI anchor and, thereby, the ultimate function of the mature protein.

scholarly journals The 54-kD protein of signal recognition particle contains a methionine-rich RNA binding domain.

1990 ◽  
Vol 111 (5) ◽  
pp. 1793-1802 ◽  
Author(s):  
K Römisch ◽  
J Webb ◽  
K Lingelbach ◽  
H Gausepohl ◽  
B Dobberstein
Keyword(s):  
Amino Acids ◽  
Rna Binding ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Binding Domain ◽  
Secretory Proteins ◽  
Signal Recognition ◽  
Rna Binding Domain ◽  
Necessary And Sufficient

Signal recognition particle (SRP) plays the key role in targeting secretory proteins to the membrane of the endoplasmic reticulum (Walter, P., and V. R. Lingappa. 1986. Annu. Rev. Cell Biol. 2:499-516). It consists of SRP7S RNA and six proteins. The 54-kD protein of SRP (SRP54) recognizes the signal sequence of nascent polypeptides. The 19-kD protein of SRP (SRP19) binds to SRP7S RNA directly and is required for the binding of SRP54 to the particle. We used deletion mutants of SRP19 and SRP54 and an in vitro assembly assay in the presence of SRP7S RNA to define the regions in both proteins which are required to form a ribonucleoprotein particle. Deletion of the 21 COOH-terminal amino acids of SRP19 does not interfere with its binding to SRP7S RNA. Further deletions abolish SRP19 binding to SRP7S RNA. The COOH-terminal 207 amino acids of SRP54 (M domain) were found to be necessary and sufficient for binding to the SRP19/7S RNA complex in vitro. Limited protease digestion of purified SRP confirmed our results for SRP54 from the in vitro binding assay. The SRP54M domain could also bind to Escherichia coli 4.5S RNA that is homologous to part of SRP7S RNA. We suggest that the methionine-rich COOH terminus of SRP54 is a RNA binding domain and that SRP19 serves to establish a binding site for SRP54 on the SRP7S RNA.

scholarly journals A Lentiviral Envelope Signal Sequence is a Tetherin Antagonizing Protein

2021 ◽  
Author(s):  
James H Morrison ◽  
Eric Murnane Poeschla
Keyword(s):  
Amino Acids ◽  
Feline Immunodeficiency Virus ◽  
Secretory Pathway ◽  
Signal Sequence ◽  
Host Protein ◽  
Enveloped Viruses ◽  
Viral Particles ◽  
Immunodeficiency Virus ◽  
Primate Lentiviruses ◽  
Necessary And Sufficient

Signal sequences are N-terminal peptides, generally less than 30 amino acids in length, that direct translocation of proteins into the endoplasmic reticulum and secretory pathway. The envelope glycoprotein (Env) of the nonprimate lentivirus Feline immunodeficiency virus (FIV) contains the longest signal sequence of all eukaryotic, prokaryotic and viral proteins (175 amino acids). The reason is unknown. Tetherin is a dual membrane-anchored host protein that inhibits the release of enveloped viruses from cells. Primate lentiviruses have evolved three antagonists: the small accessory proteins Vpu and Nef, and in the case of HIV-2, Env. Here we identify the FIV Env signal sequence (Fess) as the FIV tetherin antagonist. A short deletion in the central portion of Fess had no effect on viral replication in the absence of tetherin but severely impaired virion budding in its presence. Fess is necessary and sufficient, acting as an autonomous accessory protein with the rest of Env dispensable. In contrast to primate lentivirus tetherin antagonists, it functions by stringently blocking the incorporation of this restriction factor into viral particles rather than by degrading it or downregulating it from the plasma membrane.

Mutational analysis of the variant surface glycoprotein GPI-anchor signal sequence inTrypanosoma brucei

2002 ◽  
Vol 115 (4) ◽  
pp. 805-816 ◽  
Author(s):  
Ulrike Böhme ◽  
George A. M. Cross
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Cell Surface ◽  
Signal Sequence ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Gpi Anchor ◽  
Signal Sequences ◽  
Hydrophobic Region ◽  
High Conservation

The variant surface glycoproteins (VSG) of Trypanosoma brucei are anchored to the cell surface via a glycosylphosphatidylinositol (GPI) anchor. All GPI-anchored proteins are synthesized with a C-terminal signal sequence,which is replaced by a GPI-anchor in a rapid post-translational transamidation reaction. VSG GPI signal sequences are extraordinarily conserved. They contain either 23 or 17 amino acids, a difference that distinguishes the two major VSG classes, and consist of a spacer sequence followed by a more hydrophobic region. The ω amino acid, to which GPI is transferred, is either Ser,Asp or Asn, the ω+2 amino acid is always Ser, and the ω+7 amino acid is almost always Lys. In order to determine whether this high conservation is necessary for GPI anchoring, we introduced several mutations into the signal peptide. Surprisingly, changing the most conserved amino acids, at positions ω+1, ω+2 and ω+7, had no detectable effect on the efficiency of GPI-anchoring or on protein abundance. Several more extensive changes also had no discernable impact on GPI-anchoring. Deleting the entire 23 amino-acid signal sequence or the 15 amino-acid hydrophobic region generated proteins that were not anchored. Instead of being secreted, these truncated proteins accumulated in the endoplasmic reticulum prior to lysosomal degradation. Replacing the GPI signal sequence with a proven cell-surface membrane-spanning domain reduced expression by about 99%and resulted not in cell surface expression but in accumulation close to the flagellar pocket and in non-lysosomal compartments. These results indicate that the high conservation of the VSG GPI signal sequence is not necessary for efficient expression and GPI attachment. Instead, the GPI anchor is essential for surface expression of VSG. However, because the VSG is a major virulence factor, it is possible that small changes in the efficiency of GPI anchoring,undetectable in our experiments, might have influenced the evolution of VSG GPI signal sequences.

scholarly journals The Specificity for the Differentiation Blocking Activity of Carcinoembryonic Antigen Resides in Its Glycophosphatidyl-Inositol Anchor

2000 ◽  
Vol 150 (3) ◽  
pp. 613-626 ◽  
Author(s):  
Robert A. Screaton ◽  
Luisa DeMarte ◽  
Petr Dráber ◽  
Clifford P. Stanners
Keyword(s):  
Carcinoembryonic Antigen ◽  
Adhesion Molecule ◽  
Signal Sequence ◽  
Myogenic Differentiation ◽  
Ectopic Expression ◽  
Gpi Anchor ◽  
Ig Superfamily ◽  
Blocking Activity ◽  
Differentiation Block ◽  
Glycophosphatidyl Inositol

Ectopic expression of various members of the human carcinoembryonic antigen (CEA) family of intercellular adhesion molecules in murine myoblasts either blocks (CEA, CEACAM6) or allows (CEACAM1) myogenic differentiation. These surface glycoproteins form a subset of the immunoglobulin (Ig) superfamily and are very closely related, but differ in the precise sequence of their external domains and in their mode of anchorage to the cell membrane. CEA and CEACAM6 are glycophosphatidyl-inositol (GPI) anchored, whereas CEACAM1 is transmembrane (TM) anchored. Overexpression of GPI-linked neural cell adhesion molecule (NCAM) p125, also an adhesion molecule of the Ig superfamily, accelerates myogenic differentiation. The molecular requirements for the myogenic differentiation block were investigated using chimeric constructs in which the COOH-terminal hydrophobic domains of CEA, CEACAM1, and NCAM p125 were exchanged. The presence of the GPI signal sequence specifically from CEA in the chimeras was sufficient to convert both CEACAM1 and NCAM into differentiation-blocking proteins. Conversely, CEA could be converted into a neutral protein by exchanging its GPI anchor for the TM anchor of CEACAM1. Since the external domains of CEA, CEACAM1, and NCAM can all undergo homophilic interactions, and mutations in the self-adhesive domains of CEA abrogate its differentiation-blocking activity, the structural requirements for differentiation-inhibition are any self-adhesive domains attached to the specific GPI anchor derived from CEA. We therefore suggest that biologically significant functional information resides in the processed extreme COOH terminus of CEA and in the GPI anchor that it determines.

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