Characterization of a Region of the Measles Virus Hemagglutinin Sufficient for Its Dimerization

Abstract

Attachment of measles virus (MV) to its cellular receptor is mediated by the viral envelope glycoprotein hemagglutinin (H). H exists at the viral surface as a disulfide-linked dimer which may associate into a tetramer. We aimed to define regions of H essential for its homo-oligomerization. To delineate these more precisely, we have generated a series of H ectodomain truncation mutants and studied their abilities to form both homotypic complexes and heterotypic complexes with full-length H. We define a "minimal unit" which is sufficient for MV H dimerization as that encompassing residues 1 to 151. This unit forms both homodimers and heterodimers with full-length H protein, although neither is transported to the cell surface even in the presence of other MV proteins. We show that cysteine residues at positions 139 and 154 are both critical in mediating covalent dimerization, not only of the truncated H mutants but also of full-length MV H protein. Even those cysteine mutants unable to form covalent intermolecular interactions are biologically active, mediating the formation of syncytia, albeit at a reduced rate. We demonstrate that this impaired capacity to mediate cell-to-cell fusion is based mainly on a reduced transport rate of the mutant molecules to the cell surface, indicating a role for covalent intermolecular interactions in efficient transport of MV H dimers to the cell surface.

Distinct Kinetics for Binding of the CD46 and SLAM Receptors to Overlapping Sites in the Measles Virus Hemagglutinin Protein

“…The oligomerization state of the different MVH length variants shows that residue Cys 154 is involved in formation of soluble disulfide-linked homodimers as reported for the membrane-bound hemagglutinin (31,32). Receptors bound to monomeric and dimeric MVH variants with similar affinities and almost identical k d , indicating that the virus-receptor binding surface is located in a single virus protein and that the interaction is equimolar.…”

Identification of a Region in the Stalk Domain of the Nipah Virus Receptor Binding Protein That Is Critical for Fusion Activation

“…The oligomeric state of paramyxovirus receptor binding proteins has been shown to be essential for fusion promotion for NiV (44) and has been suggested to be critical for fusion promotion by HPIV3 (38), measles virus (65,66), and other paramyxoviruses (24). It was unknown whether, within a tetramer, the receptorengaged signal can be transmitted from the head of one monomer via the stalk of a different monomer, or whether each monomer acts individually in terms of signal transmission; the chimeric receptor binding proteins provided the answer.…”

Measles Virus Envelope Glycoproteins Hetero-oligomerize in the Endoplasmic Reticulum

“…Transport kinetics of the tagged glycoproteins were shown not to be influenced by the FLAG epitope itself (Ref. 7 and data not shown).…”