Measles Virus (MV) Hemagglutinin: Evidence that Attachment Sites for MV Receptors SLAM and CD46 Overlap on the Globular Head

Abstract

Measles virus hemagglutinin (MVH) residues potentially responsible for attachment to the wild-type (wt) MV receptor SLAM (CD150) have been identified and localized on the MVH globular head by reference to a revised hypothetical structural model for MVH (www.pepscan.nl/downloads/measlesH.pdb). We show that the mutation of five charged MVH residues which are conserved among morbillivirus H proteins has major effects on both SLAM downregulation and SLAM-dependent fusion. In the three-dimensional surface representation of the structural model, three of these residues (D505, D507, and R533) align the rim on one side of the cavity on the top surface of the MVH globular head and form the basis of a single continuous site that overlaps with the 546-548-549 CD46 binding site. We show that the overlapping sites fall within the footprint of an anti-MVH monoclonal antibody that neutralizes both wt and laboratory-vaccine MV strains and whose epitope contains R533. Our study does not exclude the possibility that Y481 binds CD46 directly but suggests that the N481Y mutation of wt MVH could influence, at a distance, the conformation of the overlapping sites so that affinity to CD46 increases. The relevance of these results to present concepts of MV receptor usage is discussed, and an explanation is proposed as to why morbillivirus attachment proteins are H, whereas those from the other paramyxoviruses are HN (hemagglutinin-neuraminidase).Measles virus (MV), a member of the genus Morbillivirus in the family Paramyxoviridae of the order Mononegavirales, possesses two glycoproteins in its envelope: the hemagglutinin (H) protein, responsible for attachment to the cellular receptors, and the fusion (F) protein, which mediates the fusion of the viral and host membranes (12, 51). Expression of the MV glycoproteins at the surface of the infected host cell also leads to cell-to-cell fusion, resulting in the formation of multinuclear giant cells (syncytium formation), which is the hallmark of paramyxoviral infections. MV fusion has been shown to depend upon the coexpression of the two glycoproteins (53), and it is believed that the fusion helper function of the MVH protein depends upon a specific and physical interaction with the MVF protein mediated via the latter's cysteine-rich region (52).The host range of MV is restricted to humans and certain large primates. MV has been shown to use two cellular proteins as receptors: CD46 and SLAM/CD150 (8,9,18,28,47). CD46 is a member of the RCA family of proteins, which control the complement cascade, whereas SLAM is a CD2 member of the immunoglobulin superfamily and plays a regulatory role in lymphocyte activation. Although CD46 is ubiquitously expressed on all human nucleated cells, the expression of SLAM appears to be restricted to certain cells of hematopoietic origin, including activated B and T lymphocytes and activated dendritic cells and monocytes (47). It is now generally accepted that whereas laboratory and vaccine strains use both SLAM and CD46 as their cellular receptors, wild-type (...

Canine Distemper Viruses Expressing a Hemagglutinin without N-Glycans Lose Virulence but Retain Immunosuppression

“…Unlike fusion or other multifunctional proteins, where N-glycans play an important role in activation (2,8,16,26,30,40,47), the paramyxovirus attachment protein does not require cleavage to be functional. Despite this, sialic acid-binding attachment proteins are more sensitive to N-glycan deletion than CDV H (27,31,39), suggesting that their N-glycans may be involved in receptor recognition and attachment, while N glycosylation has not been demonstrated to play a role in morbillivirus interaction with its protein receptors SLAM and CD46 (4,7,18,25,46,49). The observation that a completely deglycosylated H protein remains functional thus indicates a correlation between the Nglycosylation requirement and the folding and processing complexity of glycoproteins.…”

Crystal structure of measles virus hemagglutinin provides insight into effective vaccines

“…Previous studies on the receptordependent fusion-inducing activity of mutant MV-H proteins identified several amino acid residues important for interaction with SLAM: D505, D507, Y529, D530, T531, R533, F552, Y553 and P554 (23,24) (Fig. 3A).…”

“…2). On the other hand, the key residues for interaction of MV-H (Ed) with CD46 (23,24,28) span the ␤3 to ␤5 sheets of the side face of the head domain and are located differently from the key residues at the SLAM-binding site (Fig. 3B).…”

“…The structure also suggests that extensive masking by sugars limits the availability of potential epitopes on the surface of The amino acid residues predicted to be involved in receptor binding (23,24,28) are shown in magenta (SLAM) and cyan/light blue (CD46, strong/weak effect). The color scheme used is the same as Fig.…”

Dynamic Interaction of the Measles Virus Hemagglutinin with Its Receptor Signaling Lymphocytic Activation Molecule (SLAM, CD150)

“…As discussed, Ile-194, Tyr- 529, Asp-530, Thr-531, Arg-533, Tyr-553, and Pro-554 were identified based on a receptor-dependent fusion assay (15). Asp-505, Asp-507, and His-536 were initially shown only to significantly reduce SLAM-down-regulation (33). We have subsequently tested D505G and D507G mutations in a receptor-specific cell-to-cell fusion assay and confirmed that they cause a two-third decrease in SLAM-dependent fusion (data not shown).…”