Sialidases conserved sequences

B. Rothe, P. Roggentin, and R. Schauer, The sialidase gene from Clostridium septicum Cloning, sequencing, expression in Escherichia coli and identification of conserved sequences in sialidases and other proteins, Mol Gen. Genet., 226 (1991) 190-197. 

E. Tiralongo, 1. Martensen, J. Grotzinger, J. Tiralongo, and R. Schauer, Trans-sialidase-like sequences from Trypanosoma congolense conserve most of the critical active site residues found in other trans-sialidases, Biol. Chem., 384 (2003) 1203-1213. 

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,... 

Two trans-sialidases isolated from the animal-pathogenic Afiican trypanosome T. Congo lense show pronounced differences in their capacity for sialic acid transfer as compared with the hydrolytic activity. Partial sequences were obtained from these two enzymes by a PCR-based approach, showing 50% identity with each oflier, but are similar to viral, bacterial, animal siahdases and other trans-sialidases. Most of the critical active-site residues common to other trypanosomal siahdases and TS are conserved This similarity, together with the amino acid difference at the active site, between American and African (trans-)siahdases is depicted in the pubUcation. ... 

The six-bladed P-propeller-like domain is now recognized as the canonical siali-dase structure, found in each of the viral, bacterial, trypanosomal, and human exo-sialidases crystallized [63-66], despite wide differences in sequence similarities [67]. Key catalytic residues in the active site are also well conserved (reviewed in [63]). 

Antigenic determinants were found across the top surface of the sialidase monomer and encircling the active site [62], Of importance for inhibitor development, the active site was seen to contain a large number of amino acids that were conserved in all influenza A and B virus sialidase sequences known to that time [34,62]. This suggested that the active site residues were under pressure to remain constant [69], and that this was an invariant area of the sialidase that could be targeted for inhibitor development against the otherwise highly mutable [4] protein. 

Another feature common to all nonviral sialidases is the so-called Asp-box, a motif (S/T-X-D-[X]-G-X-T-W/F) that repeats one to five times along the sequences. Each Asp-box forms a clamp-like loop and they occur at topologically equivalent positions on the outside of the structure between the third and fourth p-strand of a propeller blade [12, 114, 115]. For example, in the sialidase Nani of Clostridium perfringens four Asp-boxes are located in the blades one to four (PDB ID 2BF6 [115]). However, in endosialidases only two Asp-boxes have been found in the first and fourth blade of the propeller [12], with the sequences S-G-D-D-G-Q/ K-T-W and S-X-D-X-G-X-X-W that are conserved in aU so far known endosialidases. Interestingly, in endoNF the p-barrel domain is inserted between the third and fourth p-sheet of the second blade, thereby replacing a potential Asp-box. Since the Asp-boxes are located on the back side of the propeller and remote from the active site, any functions other than structural folds have not been found as yet for these motifs. 

The crystal structures of two representative small sialidases, with molecular weights around 40 kDa, have been determined one from Salmonella typhimurium [17] and one from Micromonospora viridifaciens [I8j. These reveal the same P-propeller fold seen in the influenza virus neuraminidase (Figure 2), despite having no sequence similarity to the viral enzyme, and not containing any disulphide bonds in contrast to the seven conserved disulfides in the viral enzyme. 

Yeung, M. K., 1993, Complete nucleotide sequence of the Actinomyces viscosus T14V sialidase gene Presence of a conserved repeating sequence among strains of Actinomyces ssp., Infect. Immun. 61 109-116. 

Recently, a cDNA clone encoding the cytosolic sialidase of rat skeletal muscle was prepared and expressed in Escherichia coli (Miyagi et al., 1993). The nucleotide sequence encodes 379 amino acid residues with a calculated molecular mass of 42,381 Da. The deduced amino acid sequence does not resemble any of the viral, bacterial, or parasitic sialidases, although it contains two Asp blocks, which are conserved in these enzymes (Roggentin et al., 1989). 

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