Endosialidase NF (endoNF) is a bacteriophage-derived endosialidase that
specifically degrades alpha-2,8-linked polysialic acid. The structure of a new
crystal form of endoNF in complex with sialic acid has been refined at 0.98 A
resolution. The 210 kDa homotrimeric multi-domain enzyme displays outstanding
stability and resistance to SDS. Even at atomic resolution, only a minor
fraction of side chains possess alternative conformations. However, multiple
conformations of an active-site residue imply that it has an important catalytic
function in the cleavage mechanism of polysialic acid.