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Polysaccharide Lyase Family 6
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- Author: ^^^Emil Stender^^^
- Responsible Curator: ^^^Birte Svensson^^^
| Polysaccharide Lyase Family 6 | |
| 3D structure | parralel β-helix |
| Mechanism | β-elimination |
| Charge neutralizer | calcium or water |
| Active site residues | known |
| CAZy DB link | |
| https://www.cazy.org/PL6.html | |
Substrate specificities
PL6 currently contains 3 subfamilies [1] all of which contain members catalyzing the depolymerisation of alginate [2]. Alginate consisting of 1,4 linked β-D-mannuronic acid and α-L-guluronic acid arranged in poly-mannuronic acid blocks, poly-guluronic acid blocks or poly-mannuronic/guluronic acid blocks [3, 4]. Subfamily 2 and 3 have so far only shown specificity for poly-mannuronic/guluronic acid blocks [2], while subfamily 1 has been demonstrated to depolymerize poly-guluronic acid [5, 6], poly-mannuronic acid [7], poly-mannuronic/guluronic acid [2] as well as dermatan sulfate (formerly chrondroitin B) [2, 8, 9].
Kinetics and Mechanism
The β-elimination catalyzed by the PL6 enzymes results in the formation of a C4-C5 unsaturated sugar at the new non-reducing end. The first step is the neutralization of the acid group in the +1 subsite by a calcium [6, 9] or by water [5]. This lowers the pKa value of the C5-proton allowing for abstraction by the catalytic base (Figure 1). A catalytic acid then donates a proton to the glycosidic linkage resulting in the β-elimination. This can be done in syn with the acid and base on the same side of the sugar ring in the transition state (the case for D-mannuronic acid) or anti where they are on opposite sides of the sugar ring (the case for L-guluronic acid) [10, 11].
Catalytic Residues
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Three-dimensional structures
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Family Firsts
- First stereochemistry determination
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- First catalytic nucleophile identification
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- First general acid/base residue identification
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- First 3-D structure
- Content is to be added here.