Sialate-pyruvate lyase

Fig. 13. Metabolism scheme of sialic acids. Anabolic (solid arrow) and catabolic (dashed arrow) reactions are indicated. For literature see the text. Enzymes 1, CMP-sialate synthase (EC 2.7.7.43) 2, sialyltransferases (EC 2.4.99.1.) 3, CMP-Neu5Ac hydroxylase (EC 1.14.99.18) 4, acetyl-CoA sialate 4-0-acetyltransferase (EC 2.3.1.44) 5, acetyl-CoA sialate 7(9)-0-acetyltransferase (EC 2.3.1.45) 6,. S-adenosyl-L-methionine sialate 8-O-methyltransferase (proposed EC 2.1.1.78) 7, sialate 4- or 9-0-acetylesterases (EC 3.1.1.53) 8, sialidase (EC 3.2.1.18) 9, sialate-pyruvate lyase (aldolase EC 4.1.3.3). Both Neu5Ac and Neu5Gc can be O-acetylated by the two O-acetyltransferases. There may also exist a sulfotransferase, since sulfated sialic acids have been found in e.g. echinoderms [13,577]. ( ), Sialic-acid-accepting nascent glycoconjugate.

Slower degradation rate by sialate-pyruvate lyase [5,33,245]... 

Since the enzyme reaction is reversible, conditions for the synthesis of Neu5Ac and natural or synthetic derivatives in high yield as well as of Kdn with the aid of bacterial lyase were elaborated (see section 6.1). The recombinant and overexpressed sialate-pyruvate lyase from E. coli is now in wide use as a speeific chiral catalyst which mediates highly enantioselective aldol condensation reactions leading to a variety of sialic acids. 

Fig. 20. Proposed reaction scheme of sialate-pyruvate lyase from Clostridium perfringens. Based on data from refs. [33,892]. 

Fig. zi. 1 hree-dimensional structure of the sialate-pyruvate lyase from Escherichia coli. (top) Viewed down the (3-barrel axis from the carboxy-terminal end of this aldolase. The putative catalytic residue Lys-165 is shown in ball-and-stick representation, (bottom) Putative active site of Neu5Ac lyase showing the side chains of nine of the residues forming the surface of the pocket. Carbon atoms are white, oxygens black and nitrogens grey. From ref. [899] by permission of Current Biology Ltd., London. 

Reduction of sialidase, trans sialidase and sialate-pyruvate lyase activities Hindrance of sialic acid receptor interactions (viruses, mammals)... 

Increasing hydrophilicity Reduction of sialidase and sialate-pyruvate lyase actions Binding of viruses, bacteria, plant, invertebrate and mammalian lectins Hindering recognition by mammalian receptors Modulation of immune response Blood group determinant Tumor-associated antigen Differentiation marker... 

As shown in Fig. 13, sialic acids liberated by sialidase are degraded by the aldolase systematically named sialate (acylneuraminate)-pyruvate lyase (EC 4.1.3.3), resulting in... 

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