*1.2.2 Structure of pectinase*

The structure of pectinase (**Figure 4**) enables to understand the enzyme reaction mechanism on molecular basis and also provide information about the structural differences between enzymes that directly affect the catalytic properties of enzymes. Yoder *et al*. [26] characterized the three-dimensional structure of pectinase from *E. chrysanthemis*. The structure of pectinases composed of a domain of parallel β strands folded into a large right-handed cylinder. The inner cylinder contains seven to nine helical turns and due to distinctive arrangement of three β- strands in each turn of helix look like a prism shaped. The consecutive stands assemble to form three parallel β-sheets named PB1, PB2 and PB3. Even the mechanism of pectin degradation by three pectinases is different, the substrate binding figure out from structure, sequence similarity and site directed mutagenesis studies [27], are all observed in a similar location within cleft formed on the outer of the parallel β- helix among one side of PB1 and the overhanging loops [28].
