Sialidase three-dimensional structure

The three-dimensional structure of TcTS was determined by crystallographic studies on a fully active TcTS mutant.145 147 It consists of two domains the N-terminal catalytic domain which forms a six-bladed [1 propeller, characteristic of microbial sialidases, connected through a long a helix to a C-terminal lectin-like domain which does not participate in the enzymatic reaction. The catalytic domain... 

Fig. 17. Three-dimensional structure of Salmonella typhimurium LT2 sialidase with bound inhibitor Neu2en5Ac obtained from X-ray crystallography. From ref. [790] by permission of National Academy of Sciences, New York.

Similarly to NEUl, NEU2 contains multiple Asp-box motifs of which one is less conserved (residues 247-254) and two are eanonical Asp-boxes (residues 129-136 and 199-206). Stmcturally, Asp boxes show a (3-hairpin structure stabilized by a water molecule at the center of three eonserved residues of serine, aspartate, and tryptophan, and are found in topologically equivalent positions in all members of the sialidase gene family. Interestingly, Asp-boxes are found in protein families having different sequences and three-dimensional structures, sueh as bacterial ribonucleases, reelin,... 

The first three-dimensional structure of influenza A virus sialidase was solved in 1983 to 2.9 A resolution, using X-ray data for two crystalline N2 sialidases as pronase-released heads [61,62]. This work gave detail to the known tetrameric form of the protein. Crystals soaked with free NeuSAc, the product of catalysis, indicated that the active site was a deep pocket on the top surface of each subunit [62]. 

The three-dimensional structures of the head domains of N2, N9, and type B sialidases have been determined with high resolution (Varghese and Colman, 1991 Tulip et al., 1991 Burmeister et al., 1992). The results confirmed that these sialidases have essentially the same structure and suggest that the structure of the sialidases of other subtypes will be very similar. The head domain of a monomer is composed of six p-sheets arranged like the blades of a propeller. Each of the P-sheets is made up of four antiparallel p-strands forming a W topology and connected by short peptide loops. 

N. Takahashi, K. B. Lee, H. Nakagawa, Y. Tsukamoto, Y. Kawamura, and Y. C. Lee, Enzymatic sialylation of N-linked oligosaccharides using an alpha-(2,3)-specific trans-sialidase from Trypanosoma cruzi. structural identification using a three-dimensional elution mapping technique, Anal. Biochem., 230 (1995) 333-342. 

Crystals of pronase-released heads of the N2 human strains of A/Tokyo/3/67 [44] and A/RI/5+/57 were used for an x-ray structure determination. The x-ray 3-dimensional molecular structure of neuraminidase heads was determined [45] for these two N2 subtypes by a novel technique of molecular electron density averaging from two different crystal systems, using a combination of multiple isomorphous replacement and noncrystallographic symmetry averaging. The structure of A/Tokyo/3/67 N2 has been refined [46] to 2.2 A as has the structures of two avian N9 subtypes [47-49]. Three influenza type structures [50] have also been determined and found to have an identical fold with 60 residues (including 16 conserved cysteine residues) being invariant. Bacterial sialidases from salmonella [51] and cholera [52] have homologous structures to influenza neuraminidase, but few of the residues are structurally invariant. 

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