Pectin deconstruction is the initial step in breaking the recalcitrance of plant biomass by using selected microorganisms that carry pectinolytic enzymes. Pectate lyases that cleave α-1,4-galacturonosidic linkage of pectin are widely used in industries, such as paper making and fruit softening. However, reports on pectate lyases with high thermostability are few. Two pectate lyases (CbPL3 and CbPL9) from a thermophilic bacterium Caldicellulosiruptor bescii were investigated. Although these two enzymes belonged to different families of polysaccharide lyase, both were Ca2+-dependent. Similar biochemical properties were shown under optimized conditions 80 °C - 85 °C and pH 8-9. However, the degradation products on pectin and polygalacturonic acids (pGA) were different, revealing the distinct mode of action. A concanavalin A-like lectin/glucanase (CALG) domain, located in the N-terminus of two CbPLs, shares 100% amino acid identity. CALG-truncated mutant of CbPL9 showed lower activities than the wild-type, whereas the CbPL3 with CALG knock-out portion was reported with enhanced activities, thereby revealing the different roles of CALG in two CbPLs. I-TASSER predicted that the CALG in two CbPLs is structurally close to the family 66 carbohydrate binding module (CBM66). Furthermore, substrate-binding assay indicated that the catalytic domains in two CbPLs had strong affinities on pectate-related substrates, but CALG showed weak interaction with a number of lignocellulosic carbohydrates, except sodium carboxymethyl cellulose and sodium alginate. Finally, scanning electron microscope analysis and total reducing sugar assay showed that the two enzymes could improve the saccharification of switchgrass. The two CbPLs are impressive sources for degradation of plant biomass.
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