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netLibrary - eBook Summary Structure-based Drug Design by ...

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Figure 4<br />

A CPK model of two tetramers of A/Tokyo/3/67 neuraminidase heads as seen<br />

in the crystal structure. The four carbohydrate spikes emanating from the top<br />

of the molecule (at Asn146) interdigitate and form an open “barrel” structure.<br />

They form an unusual crystal contact. The dark spheres represent carbohydrate<br />

and the light spheres represent protein. The carbohydrate at Asn200 starts<br />

from one subunit and covers a neighboring subunit on the same tetramer. The<br />

other carbohydrates lie on the<br />

underside of the tetramer.<br />

Page 468<br />

[63,64]. The oligosaccharide appears as a spike emanating from the top of the monomer, forming a<br />

crystal contact with a neighboring tetramer in crystals of A/Tokyo/3/67 neuraminidase. The four<br />

carbohydrate spikes of a tetramer form an open “barrel” structure of eight carbohydrate chains with the<br />

neighboring tetramer, with no apparent intercarbohydrate contacts. This oligosaccharide may play an<br />

important but as yet unidentified role in neuraminidase structure or activity.<br />

D. Antigenic Variation in Neuraminidase <strong>Structure</strong>s<br />

Comparison of all known sequences of approximately 390 residues of the neuraminidase globular head<br />

[24], indicates that only 54 (excluding 16 conserved cysteine residues) are invariant (Figure 5a). Apart<br />

from 21 residues involved<br />

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