11 research outputs found
O-linked glycoproteins of the nuclear pore complex interact with a cytosolic factor required for nuclear protein import.
Varicellovirus UL49.5 Proteins Differentially Affect the Function of the Transporter Associated with Antigen Processing, TAP
Cytotoxic T-lymphocytes play an important role in the protection against viral infections, which they detect through the recognition of virus-derived peptides, presented in the context of MHC class I molecules at the surface of the infected cell. The transporter associated with antigen processing (TAP) plays an essential role in MHC class I–restricted antigen presentation, as TAP imports peptides into the ER, where peptide loading of MHC class I molecules takes place. In this study, the UL49.5 proteins of the varicelloviruses bovine herpesvirus 1 (BHV-1), pseudorabies virus (PRV), and equine herpesvirus 1 and 4 (EHV-1 and EHV-4) are characterized as members of a novel class of viral immune evasion proteins. These UL49.5 proteins interfere with MHC class I antigen presentation by blocking the supply of antigenic peptides through inhibition of TAP. BHV-1, PRV, and EHV-1 recombinant viruses lacking UL49.5 no longer interfere with peptide transport. Combined with the observation that the individually expressed UL49.5 proteins block TAP as well, these data indicate that UL49.5 is the viral factor that is both necessary and sufficient to abolish TAP function during productive infection by these viruses. The mechanisms through which the UL49.5 proteins of BHV-1, PRV, EHV-1, and EHV-4 block TAP exhibit surprising diversity. BHV-1 UL49.5 targets TAP for proteasomal degradation, whereas EHV-1 and EHV-4 UL49.5 interfere with the binding of ATP to TAP. In contrast, TAP stability and ATP recruitment are not affected by PRV UL49.5, although it has the capacity to arrest the peptide transporter in a translocation-incompetent state, a property shared with the BHV-1 and EHV-1 UL49.5. Taken together, these results classify the UL49.5 gene products of BHV-1, PRV, EHV-1, and EHV-4 as members of a novel family of viral immune evasion proteins, inhibiting TAP through a variety of mechanisms
Structural analysis of the p62 complex, an assembly of O-linked glycoproteins that localizes near the central gated channel of the nuclear pore complex.
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Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist
RationaleGq signaling in cardiac myocytes is classically considered toxic. Targeting Gq directly to test this is problematic, because cardiac myocytes have many Gq-coupled receptors.ObjectiveTest whether Gq coupling is required for the cardioprotective effects of an alpha-1A-AR (adrenergic receptor) agonist.Methods and resultsIn recombinant cells, a mouse alpha-1A-AR with a 6-residue substitution in the third intracellular loop does not couple to Gq signaling. Here we studied a knockin mouse with this alpha-1A-AR mutation. Heart alpha-1A receptor levels and antagonist affinity in the knockin were identical to wild-type. In wild-type cardiac myocytes, the selective alpha-1A agonist A61603-stimulated phosphoinositide-phospholipase C and myocyte contraction. In myocytes with the alpha-1A knockin, both A61603 effects were absent, indicating that Gq coupling was absent. Surprisingly, A61603 activation of cardioprotective ERK (extracellular signal-regulated kinase) was markedly impaired in the KI mutant myocytes, and A61603 did not protect mutant myocytes from doxorubicin toxicity in vitro. Similarly, mice with the α1A KI mutation had increased mortality after transverse aortic constriction, and A61603 did not rescue cardiac function in mice with the Gq coupling-defective alpha-1A receptor.ConclusionsGq coupling is required for cardioprotection by an alpha-1A-AR agonist. Gq signaling can be adaptive
Structural Basis of Small-Molecule Aggregate Induced Inhibition of a Protein–Protein Interaction
A prevalent observation
in high-throughput screening and drug discovery
programs is the inhibition of protein function by small-molecule compound
aggregation. Here, we present the X-ray structural description of
aggregation-based inhibition of a protein–protein interaction
involving tumor necrosis factor α (TNFα). An ordered conglomerate
of an aggregating small-molecule inhibitor (JNJ525) induces a quaternary
structure switch of TNFα that inhibits the protein–protein
interaction between TNFα and TNFα receptors. SPD-304 may
employ a similar mechanism of inhibition