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Polysaccharide lyases (PLs) cleave uronic acid-containing polysaccharides via a β-elimination mechanism to generate an unsaturated hexenuronic acid residue and a new reducing end at the point of cleavage [1, 2]. PLs have been grouped into families and subfamilies within the Carbohydrate-Active Enzyme (CAZy) framework and that the PLs included are restricted to those operating via syn- and anti-elimination mechanisms . In this way, they are distinct from carbon-oxygen lyases that modify polysaccharide composition. Broadly, the mechanism of PL action can be described as consisting of three events: (i) abstraction of the C-5 proton on the sugar ring of a uronic acid or ester by a charge stabilizing cation such as Ca2+ or a basic amino acid side chain, (ii) stabilization of the resulting anion by charge delocalization onto the C-6 carbonyl group, and (iii) lytic cleavage of the O-4:C-4 bonding that is facilitated by proton donation from a catalytic acid [1, 3]. Please see the following reviews on PL classification, specificities, mechanisms, and structures [1, 2, 3, 4].
- Lombard V, Bernard T, Rancurel C, Brumer H, Coutinho PM, and Henrissat B. (2010). A hierarchical classification of polysaccharide lyases for glycogenomics. Biochem J. 2010;432(3):437-44. DOI:10.1042/BJ20101185 |
- Garron ML and Cygler M. (2010). Structural and mechanistic classification of uronic acid-containing polysaccharide lyases. Glycobiology. 2010;20(12):1547-73. DOI:10.1093/glycob/cwq122 |
- Yip VL and Withers SG. (2006). Breakdown of oligosaccharides by the process of elimination. Curr Opin Chem Biol. 2006;10(2):147-55. DOI:10.1016/j.cbpa.2006.02.005 |
- Garron ML and Cygler M. (2014). Uronic polysaccharide degrading enzymes. Curr Opin Struct Biol. 2014;28:87-95. DOI:10.1016/j.sbi.2014.07.012 |