Human Herpesvirus 7 U21 Tetramerizes To Associate with Class I Major Histocompatibility Complex Molecules

Abstract

The U21 gene product from human herpesvirus 7 binds to and redirects class I major histocompatibility complex (MHC) molecules to a lysosomal compartment. The molecular mechanism by which U21 reroutes class I MHC molecules to lysosomes is not known. Here, we have reconstituted the interaction between purified soluble U21 and class I MHC molecules, suggesting that U21 does not require additional cellular proteins to interact with class I MHC molecules. Our results demonstrate that U21, itself predicted to contain an MHC class I-like protein fold, interacts tightly with class I MHC molecules as a tetramer, in a 4:2 stoichiometry. These observations have helped to elucidate a refined model describing the mechanism by which U21 escorts class I MHC molecules to the lysosomal compartment. IMPORTANCEIn this report, we show that the human herpesvirus 7 (HHV-7) immunoevasin U21, itself a class I MHC-like protein, binds with high affinity to class I MHC molecules as a tetramer and escorts them to lysosomes, where they are degraded. While many class I MHC-like molecules have been described in detail, this unusual viral class I-like protein functions as a tetramer, associating with class I MHC molecules in a 4:2 ratio, illuminating a functional significance of homooligomerization of a class I MHC-like protein.

Combining biophysical methods for the analysis of protein complex stoichiometry and affinity inSEDPHAT

“…1), especially for multi-component systems. This unique advantage has been demonstrated in various multi-component protein systems (Houtman et al, 2006;Brautigam et al, 2009;Barda-Saad et al, 2010;May et al, 2014).…”

“…The integration of c k (s) reports the concentration of components co-sedimenting in a certain peak. Details for the application of this multi-signal SV (MSSV) approach and requirements for spectral resolution can be found in Padrick & Brautigam 2011 Example of the MSSV analysis of MHC class I (blue) binding to HHV-7 U21 (red) forming mixed 4:2 complexes (May et al, 2014). The insets show raw boundary profiles from the Rayleigh interference optical system (left) and absorbance system at 280 nm (right).…”

“…For ITC, we have demonstrated how this can substantially improve the level of detail and reveal the cooperativity parameters in ternary multiprotein complexes (Houtman et al, 2007); in sedimentation equilibrium analytical ultracentrifugation (SE) SEDPHAT has been routinely used in global analysis to overcome the limitation of ill-conditioned SE data and obtain better determination of thermodynamic parameters (Vistica et al, 2004;Ghirlando, 2011;Zhao, Brautigam et al, 2013); and multiple approaches for global analysis in sedimentation velocity analytical ultracentrifugation (SV) include direct boundary modeling with Lamm equation solutions for determining equilibrium and kinetic binding constants, as well as hydrodynamic shape parameters (Schuck, 2003;Dam et al, 2005;Brautigam, 2011), multi-signal analysis (MSSV) for determining the number and composition of co-existing complexes (Balbo et al, 2005; and global density-contrast analysis for determining macromolecular partial specific volume (Brown et al, 2011). Finally, applications of global analysis of combined SE and SV data in SEDPHAT have demonstrated the utility of a more generalized sedimentation analysis (Canzio et al, 2013;May et al, 2014).…”

Evasion of the Host Immune Response by Betaherpesviruses

“…It had previously been established that U21 oligomerizes with MHC class I complexes [ 134 ] and that oligomerized Golgi proteins are targeted to lysosomes for degradation [ 135 ]. This led to the hypothesis that the U21/MHC class I oligomers exit the Golgi apparatus in lysosome-bound vesicles [ 133 ].…”

Human Herpesvirus 6B U26 Inhibits the Activation of the RLR/MAVS Signaling Pathway

“…U20 is necessary for HHV-6-induced inhibition of tumor necrosis factor (TNF) receptor-dependent signaling and apoptosis ( 32 ). An HHV-6 U21 homolog is present in HHV-7, and both of them could divert major histocompatibility complex (MHC) class I molecules to a lysosomal compartment, which contributes to recognition escape by cytotoxic T lymphocytes (CTLs) ( 33 , 34 ). U24 inhibits CD3 recycling to the cell surface and mediates T cell receptor (TCR) at early endosomes, which prevents the activation of T cells ( 35 ).…”