Pectate lyases, isolated from Bacillus subtilis, are extracellular excretions responsible for the degradation of the pectin component in the plant cell wall, through a b-elimination mechanism. This is done through eliminative cleavage of pectate to give oligosacchsrides with 4-deoxy-alpha-D-gluc-4-enuronosyl groups at their non reducing ends, and are found in pentose and glucuronate interconversions(6). This lyase is in the mainly beta class and has a three solenoid architecture. It is isolated from the Bacillus subtilis and has a pectate lyase C-like topology and belongs to the single-stranded right-handed beta-helix, Pectin-lyase like homologous superfamily(1).
The structure consists of a parallel beta helix domain and a loop region.
The folding results in the formation of a cleft between the parallel beta-helix domain and the loops.
Calcium binds inside this cleft and is essential for the enzyme activity.
It is believed to lower the pka of arginine residue 217.(7) This residue can than act as the base for the ß-elimination mechanism which is responsible for proton abstraction during catalysis.
The amino acids associated with catalytic properties are clustered into two well- separated regions on the lyase structure, which suggests two distinct enzymatic functions.(8)