Crystal Structure of the Human Cytosolic Sialidase Neu2

In NEU2, Asp97 is found on a loop that is disordered in the apo protein but points into the active site upon substrate binding.

“In NEU2, Asp97 is found on a loop that is disordered in the apo protein but points into the active site upon substrate binding (11).”

The murine NEU1 crystal structure is most similar to that of human NEU2 and, to a lesser extent, to the Aspergillus fumigatus sialidase.

“the murine NEU1 crystal structure is most similar to that of human NEU2 (fig. S1A) (11) and, to a lesser extent, to the Aspergillus fumigatus sialidase (67).”

Comparison to human NEU2-DANA confirms that the positions and orientations of the catalytic residues are conserved in NEU1, with the important exception of Asp97.

“a comparison to the structure of human NEU2 in complex with the sialate-like inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (DANA) (11) confirms that the positions and orientations of all these residues are conserved in NEU1 (Fig. 2A), with the important exception of Asp97.”

The catalytic loop transitions from disordered to ordered upon substrate binding to NEU2, but in other eukaryotic sialidases of the GH33 family, this loop is productively positioned even without substrate.

“The corresponding loop transitions from disordered to ordered upon substrate binding to NEU2 (11), but in other eukaryotic sialidases of the GH33 family, this loop is productively positioned even without substrate (65–68).”

Residues responsible for catalysis and stabilization of the sialate carboxyl group are conserved across the sialidase superfamily, while amino acids interacting with the N-acetyl and glycerol moieties are divergent.

“Although the residues responsible for catalysis and stabilization of the sialate carboxyl group are conserved across the sialidase superfamily, amino acids that interact with the opposite side of the substrate, namely, its N-acetyl and glycerol moieties (Fig. 1B), are divergent (11).”

The NEU1 oligomerization mode is unrelated to viral sialidase tetramers, disulfide-mediated NEU3 dimers, or the various lattice interfaces observed in NEU2 crystal structures.

“The NEU1 oligomerization mode is unrelated to viral sialidase tetramers (62), disulfide-mediated NEU3 dimers (9), or the various lattice interfaces observed in NEU2 crystal structures (11, 75, 76), raising the possibility that NEU1 self-association may be required for complex formation with CTSA.”