The carboxy-terminal 18 amino acids of the measles virus hemagglutinin are essential for its biological function

Role of sialic acid-containing molecules in paramyxovirus entry into the host cell: A minireview

Sialic acid-containing compounds play a key role in the initial steps of the paramyxovirus life cycle. As enveloped viruses, their entry into the host cell consists of two main events: binding to the host cell and membrane fusion. Virus adsorption occurs at the surface of the host cell with the recognition of specific receptor molecules located at the cell membrane by specific viral attachment proteins. The viral attachment protein present in some paramyxoviruses (Respirovirus, Rubulavirus and Avulavirus) is the HN glycoprotein, which binds to cellular sialic acid-containing molecules and exhibits sialidase and fusion promotion activities. Gangliosides of the gangliotetraose series bearing the sialic acid N-acetylneuraminic (Neu5Ac) on the terminal galactose attached in alpha2-3 linkage, such as GD1a, GT1b, and GQ1b, and neolacto-series gangliosides are the major receptors for Sendai virus. Much less is known about the receptors for other paramyxoviruses than for Sendai virus. Human parainfluenza viruses 1 and 3 preferentially recognize oligosaccharides containing N-acetyllactosaminoglycan branches with terminal Neu5Acalpha2-3Gal. In the case of Newcastle disease virus, has been reported the absence of a specific pattern of the gangliosides that interact with the virus. Additionally, several works have described the use of sialylated glycoproteins as paramyxovirus receptors. Accordingly, the design of specific sialic acid analogs to inhibit the sialidase and/or receptor binding activity of viral attachment proteins is an important antiviral strategy. In spite of all these data, the exact nature of paramyxovirus receptors, apart from their sialylated nature, and the mechanism(s) of viral attachment to the cell surface are poorly understood.

Large-scale preparation of biologically active measles virus haemagglutinin expressed by attenuated vaccinia virus vectors

A procedure described here allows the efficient and rapid purification of histidine-tagged measles virus haemagglutinin that is synthesized under the control of powerful promoters (PSFJ1-10 and PSFJ2-16) of the highly attenuated vaccinia virus (VV) strain LC16mO. A single affinity chromatography step purifies recombinant haemagglutinin proteins from the lysates of cells infected with the recombinant VVs. The recovery and purity are both very high (a yield of 0.5-2.8 mg/10(8) cells and purity of >94-98%), indicating that this procedure is approximately 400 times more efficient than the conventional methods used to prepare haemagglutinin. The haemagglutinins are correctly transported to the cell surface and have haemadsorption activity. Moreover, the recombinant haemagglutinin proteins cooperate with the measles virus fusion protein to elicit cell fusion activity. In addition, the antibody titres against measles virus, as measured by enzyme-linked immunosorbent assay using the purified haemagglutinin as the capture antigen, correlated closely with neutralization test titres (R(2) = 0.84, p < 0.05), indicating the preservation of immunologically relevant antigenicity. Such recombinant haemagglutinin preparations will be useful in diagnostic tests that measure functional anti-measles immunity and investigate the biological functions and structure of the haemagglutinin.

Structural and functional studies of the measles virus hemagglutinin: identification of a novel site required for CD46 interaction

The entry of measles virus (MV) into human cells is mediated by the initial attachment of the viral hemagglutinin (HA) to the complement regulatory protein CD46. Two subdomains, one each within CD46 short consensus repeats (SCRs) 1 and 2, are responsible for this interaction. However, little is known about the regions within MV HA needed for a high-affinity CD46 interaction. To better define the HA-CD46 interaction, we took three approaches: chimeric domain swapping, peptide scanning, and alanine scanning mutagenesis. Chimeras of MV HA and the closely related rinderpest virus (RPV) HA were generated and tested for cell surface expression and the ability to hemadsorb CD46+ red blood cells (RBC). Exchanges with the N terminus of RPV were tolerated as MV HA could be replaced with RPV HA up to amino-acid position 154. However, both larger swaps with RPV and a small RPV HA replacement at the C terminus aborted cell-surface expression. Peptide scanning with 51 overlapping peptides derived from three MV HA regions showed one peptide, corresponding to MV HA amino acids 468-487, blocked hemagglutination of African green monkey (AGM) RBCs and inhibited MV infection of Chinese hamster ovary cells (CHO) expressing human CD46. Alanine scanning mutants mapped sites on the MV HA that were not required for trafficking to the cell surface or function in hemagglutination as well as a novel site required for CD46 interaction, amino acids 473-477.