title: Specific residues of a conserved domain in the N terminus of the human cytomegalovirus pUL50 protein determine its intranuclear interaction with pUL53.
abstract: Herpesviral capsids are assembled in the host cell nucleus and are subsequently translocated to the cytoplasm. During this process it has been demonstrated that the human cytomegalovirus proteins pUL50 and pUL53 interact and form, together with other viral and cellular proteins, the nuclear egress complex at the nuclear envelope. In this study we provide evidence that specific residues of a conserved N-terminal region of pUL50 determine its intranuclear interaction with pUL53. In silico evaluation and biophysical analyses suggested that the conserved region forms a regular secondary structure adopting a globular fold. Importantly, site-directed replacement of individual amino acids by alanine indicated a strong functional influence of specific residues inside this globular domain. In particular, mutation of the widely conserved residues Glu-56 or Tyr-57 led to a loss of interaction with pUL53. Consistent with the loss of binding properties, mutants E56A and Y57A showed a defective function in the recruitment of pUL53 to the nuclear envelope in expression plasmid-transfected and human cytomegalovirus-infected cells. In addition, in silico analysis suggested that residues 3-20 form an amphipathic α-helix that appears to be conserved among Herpesviridae. Point mutants revealed a structural role of this N-terminal α-helix for pUL50 stability rather than a direct role in the binding of pUL53. In contrast, the central part of the globular domain including Glu-56 and Tyr-57 is directly responsible for the functional interaction with pUL53 and thus determines formation of the basic nuclear egress complex.
authors.affiliation: Institute for Clinical and Molecular Virology, Division of Biotechnology, University of Erlangen-Nuremberg, 91054 Erlangen, Germany. jens.milbradt@viro.med.uni-erlangen.de
authors.forename: Jens
authors.initials: J
authors.lastname: Milbradt
authors.forename: Sabrina
authors.initials: S
authors.lastname: Auerochs
authors.forename: Madhumati
authors.initials: M
authors.lastname: Sevvana
authors.forename: Yves A
authors.initials: YA
authors.lastname: Muller
authors.forename: Heinrich
authors.initials: H
authors.lastname: Sticht
authors.forename: Manfred
authors.initials: M
authors.lastname: Marschall
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002467:Cell Nucleus / Q000821:virology; D017124:Conserved Sequence / Q000235:genetics; D003587:Cytomegalovirus / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D014764:Viral Proteins; C523758:pUL50 protein, cytomegalovirus; C523759:pUL53 protein, cytomegalovirus; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; D014443:Tyrosine