Hemagglutinin, trimer

The hemagglutinin trimer molecule is 135 A long (from membrane to tip) and varies in cross-section between 15 A and 40 A. It is thus an unusually... 

Danieli, T., Pelletier, Herds, Y.I. and White, J.M. (1996) Membrane fusion mediated by the influenza virus hemagglutinin requires the action of at least three hemagglutinin trimers. J. Cell Biol., 133, 559-569. 

Fio. 1. (a) A view of the influenza virus hemagglutinin trimer showing jV-acetylneuraminic acid (3, in CPK form) bound, (b) The tetrameric unit of influenza A virus sialidase. The figures were generated using the PyMOL Molecular Graphics System (Delano, W.L. (2002) at http // www.pymol.org). 

Fig. 5-7 A diagrammatic representation of the hemagglutinin trimer from the influenza virus.

Imai M, Mizuno T, Kawasaki K (2006) Membrane fusion by single influenza hemagglutinin trimers. Kinetic evidence from image analysis of hemagglutinin-reconstituted vesicles. J Biol... 

Influenza virus particles are spheroidal and approximately 100 nm in diameter. The outer-membrane envelope contains 500 copies of hemagglutinin (HA) trimers and 100 copies of neuraminidase tetramers. The hemagglutinin constitutes the receptor sites for a-sialoside ligands. X-ray analyses show that the three sialic acid binding pockets reside 46 A apart, each trimer being separated on the virion surface by about 65-110 A [42],... 

Coiled-coil motifs have been known to play roles in conformational switching in natural proteins for some time (Oas and Endow, 1994). The key examples are influenza hemagglutinin (Bullough et al., 1994 Carr and Kim, 1993 Carr et al., 1997), and the heat shock transcription factor (Rabindran et al., 1993). Furthermore, an engineered form of GCN4-pl, with Asn-16 replaced by Ala, switches from dimer to trimer upon addition of... 

E. Borrego-Diaz, M. E. Peeples, R. M. Markosyan, G. B. Melikyan, and F. S. Cohen, Completion of trimeric hairpin formation of influenza virus hemagglutinin promotes fusion pore opening and enlargement, Virology, 316 (2003) 234-244. 

Elegant studies have been carried out to investigate the structural and biochemical aspects of virus-cell fusion. Although influenza virus hemagglutinin and human immunodeficiency virus (HIV) gpl20 have been the best-studied models, numerous examples of this class I type fusion mechanism have been described. These experiments have shown that fusion is initiated by the formation of a trimeric coiled-coil helix adjacent to the fusion peptide on the virus exterior, the insertion of this fusion peptide into the host cell membrane, and the subsequent formation of a six-helix bundle (Skehel and Wiley, 1998). 

Chapman and Liljas, Fig. 8. The structure of influenza hemagglutinin (Wilson et al., 1981). The strands of the jelly-roll domain (top) are denoted 1 through 8. The color scheme is blue to red from the N terminus of chain 1 (Nt 1) to the C terminus of chain 2 (Ct 2), which is cleaved from the membrane anchor. The fusion peptide is at the N terminus of chain 2 (Nt 2). In the virus, the protein forms a trimer where the long helices are parallel to the 3-fold axis and form a stem. 

Influenza viruses are surrounded by an envelope consisting of a phospholipid bilayer and embedded viral proteins. The large spikes seen in this electron micrograph of a negatively stained influenza virion are composed of neuraminidase, a tetrameric protein, or hemagglutinin, a trimeric protein (see Figure 3-7). Inside is the helical nucleocapsid. [Courtesy of A. Helenius and J. White.]... 

Fig. 1 Sialic acid binding sites of the hemagglutinin (a) and the neuraminidase (b) of influenza A virus and the hemagglutinin-esterase-fusion protein of influenza C virus (c). Molecular surfaces of HA and HEF trimers and the NA tetramer are shown. Receptor-binding sites of HA, HEF and the hemadsorption site of NA are colored ye/tow. The catalytic sites of NA and HEF are colored green. Sialic acid moieties in the binding sites of HA and NA are shown as stick models. The figtffe is based on crystal structures IMQM, 1W20, and IFLC from Protein Data Bank...

Influenza virus A is the primary causative agent responsible for serious cases of human influenza. The influenza infection is initiated by attachment of the virus to the mammalian cell membrane through a process known as hemagglutination. The hemagglutination process is a multivalent interaction between trimers of hemagglutinin (a carbohydrate binding protein present on the viral surface) with multiple sialic acid groups present on the surface of the mammalian epithelial cell. These sialic acid residues are parts of... 

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