Polysaccharide Lyases (EC 4.2.2.-) are a group of enzymes that cleave uronic acid-containing polysaccharide chains via a β-elimination mechanism to generate an unsaturated hexenuronic acid residue and a new reducing end. This section of the CAZy database presents a classification of these enzymes in families and subfamilies based on amino acid sequence similarities, intended to reflect their structural features .
These enzymes show a large variety of fold types (or classes)  , suggesting that PLs have been invented more than once during evolution from totally different scaffolds.
Just as for the glycoside hydrolases and the glycosyltransferases, the sequence-based families of polysaccharide lyases are frequently polyspecific (i.e. contain enzymes acting on different substrates or that generate different products). Grouping into mostly monospecific subfamilies described in  provides an effort to palliate this polyspecificity. Subfamily information is provided throughout the ensemble of the polysaccharide lyase families described so far.
For the purpose of this family classification, the scope of the term PL is restricted to those enzymes which operate according to the general syn- and anti-elimination mechanisms described in , to produce a terminal hexenuronic acid moiety by β-elimination. This constitutes a clear distinction from the broader IUBMB classification of carbon-oxygen lyases acting on polysaccharides under EC 4.2.2.-, where other enzyme mechanisms have been described. Several of the lyases non-included in this classification present mechanistic commonality with glycoside hydrolases and have therefore been included among these families.
Tables for Direct Access
PL Family Number
PL Classification Statistics
|Modules in present families|| 3814|
|Non-Classified modules|| 189|
EC Activities found in PL families
Caution : Because of the modular nature of CAZymes, these activities may not be directly associated with the family but simply borne by adjacent modules.
 Lombard V, Bernard T, Rancurel C, Brumer H, Coutinho PM, Henrissat B (2010) A hierarchical classification of polysaccharide lyases for glycogenomics. Biochem. J. 432:437-444 [PMID: 20925655].
 Garron ML, Cygler M (2010) Structural and mechanistic classification of uronic acid-containing polysaccharide lyases Glycobiology, 20:1547-73 [PMID: 20805221].