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THREE-DIMENSIONAL STRUCTURE OF INFLUENZA A N9 NEURAMINIDASE AND ITS COMPLEX WITH THE INHIBITOR 2-DEOXY 2,3-DEHYDRO-N-ACETYL NEURAMINIC ACID
[NRAM_I75A5] Catalyzes the removal of terminal sialic acid residues from viral and cellular glycoconjugates. Cleaves off the terminal sialic acids on the glycosylated HA during virus budding to facilitate virus release. Additionally helps virus spread through the circulation by further removing sialic acids from the cell surface. These cleavages prevent self-aggregation and ensure the efficient spread of the progeny virus from cell to cell. Otherwise, infection would be limited to one round of replication. Described as a receptor-destroying enzyme because it cleaves a terminal sialic acid from the cellular receptors. May facilitate viral invasion of the upper airways by cleaving the sialic acid moities on the mucin of the airway epithelial cells. Likely to plays a role in the budding process through its association with lipid rafts during intracellular transport. May additionally display a raft-association independent effect on budding. Plays a role in the determination of host range restriction on replication and virulence. Sialidase activity in late endosome/lysosome traffic seems to enhance virus replication.
Publication Abstract from PubMed
We present here the three-dimensional structure of neuraminidase (E.C. 188.8.131.52) from influenza virus A/Tern/Australia/G70c/75 (N9), determined by the method of multiple isomorphous replacement, and the structure of the neuraminidase complexed with an inhibitor, 2-deoxy-2,3-dehydro-N-acetyl neuraminic acid (DANA). Native and inhibitor complex crystals are isomorphous and belong to space group I432 with unit cell dimensions of 183.78 A. The native enzyme structure and the inhibitor complex structure have been refined at 2.5 A and 2.8 A resolution, respectively, with crystallographic R-factor values of 0.193 for the native enzyme, and 0.179 for the inhibitor complex. The current enzyme model includes 387 amino acid residues which comprise the asymmetric unit. The root-mean-square deviation from ideal values is 0.013 A for bond lengths and 1.6 degree for bond angles. The neuraminidase (NA), as proteolytically cleaved from the virus, retains full enzymatic and antigenic activity, and is a box-shaped tetramer with edge lengths of 90 A and a maximal depth of 60 A. The NA tetramers are composed of crystallographically equivalent monomers related by circular 4-fold symmetry. Each monomer folds into six antiparallel beta-sheets of four strands. The secondary structure composition is 50% beta-sheet. The remaining 50% of the residues form 24 strand-connecting loops or turns. One of the loops contains a small alpha-helix. The structure of the complex of NA with DANA, a transition state analog, has enabled us to identify and characterize the site of enzyme catalysis. The center of mass of bound inhibitor is 32 A from the 4-fold axis of the tetramer, lodged at the end of a shallow crater of diameter 16 A with a depth of 8 to 10 A. There are 12 amino acid residues that directly bind DANA, with a further six conserved amino acids lining the active site pocket. The neuraminidase inhibitor complex provides a three-dimensional model which will be used to further the understanding of enzymatic hydrolysis and aid the design of specific, antineuraminidase antiviral compounds.
Three-dimensional structure of influenza A N9 neuraminidase and its complex with the inhibitor 2-deoxy 2,3-dehydro-N-acetyl neuraminic acid.,Bossart-Whitaker P, Carson M, Babu YS, Smith CD, Laver WG, Air GM J Mol Biol. 1993 Aug 20;232(4):1069-83. PMID:8371267
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.