title: Crystal structure of cytomegalovirus IE1 protein reveals targeting of TRIM family member PML via coiled-coil interactions.
abstract: PML nuclear bodies (PML-NBs) are enigmatic structures of the cell nucleus that act as key mediators of intrinsic immunity against viral pathogens. PML itself is a member of the E3-ligase TRIM family of proteins that regulates a variety of innate immune signaling pathways. Consequently, viruses have evolved effector proteins to modify PML-NBs; however, little is known concerning structure-function relationships of viral antagonists. The herpesvirus human cytomegalovirus (HCMV) expresses the abundant immediate-early protein IE1 that colocalizes with PML-NBs and induces their dispersal, which correlates with the antagonization of NB-mediated intrinsic immunity. Here, we delineate the molecular basis for this antagonization by presenting the first crystal structure for the evolutionary conserved primate cytomegalovirus IE1 proteins. We show that IE1 consists of a globular core (IE1CORE) flanked by intrinsically disordered regions. The 2.3 Å crystal structure of IE1CORE displays an all α-helical, femur-shaped fold, which lacks overall fold similarity with known protein structures, but shares secondary structure features recently observed in the coiled-coil domain of TRIM proteins. Yeast two-hybrid and coimmunoprecipitation experiments demonstrate that IE1CORE binds efficiently to the TRIM family member PML, and is able to induce PML deSUMOylation. Intriguingly, this results in the release of NB-associated proteins into the nucleoplasm, but not of PML itself. Importantly, we show that PML deSUMOylation by IE1CORE is sufficient to antagonize PML-NB-instituted intrinsic immunity. Moreover, co-immunoprecipitation experiments demonstrate that IE1CORE binds via the coiled-coil domain to PML and also interacts with TRIM5α We propose that IE1CORE sequesters PML and possibly other TRIM family members via structural mimicry using an extended binding surface formed by the coiled-coil region. This mode of interaction might render the antagonizing activity less susceptible to mutational escape.
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Myriam
authors.initials: M
authors.lastname: Scherer
authors.affiliation: Division of Biotechnology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Klingl
authors.affiliation: Division of Biotechnology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Madhumati
authors.initials: M
authors.lastname: Sevvana
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Victoria
authors.initials: V
authors.lastname: Otto
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Schilling
authors.affiliation: Division of Bioinformatics, Institute of Biochemistry, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Joachim D
authors.initials: JD
authors.lastname: Stump
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Regina
authors.initials: R
authors.lastname: Müller
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Reuter
authors.affiliation: Division of Bioinformatics, Institute of Biochemistry, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Sticht
authors.affiliation: Division of Biotechnology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Yves A
authors.initials: YA
authors.lastname: Muller
authors.affiliation: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stamminger
mesh_terms: D000090103:Antiviral Restriction Factors; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D018360:Crystallography, X-Ray; D003587:Cytomegalovirus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D045586:Intranuclear Inclusion Bodies / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases
chemical_list: D000090103:Antiviral Restriction Factors; D002352:Carrier Proteins; C088645:IE1 protein, cytomegalovirus; D017874:Immediate-Early Proteins; D000070584:Tripartite Motif Proteins; C477346:TRIM5 protein, human; D044767:Ubiquitin-Protein Ligases