Effects of module truncation on biochemical characteristics and products distribution of a new alginate lyase with two catalytic modules

In this work, we investigated the functions of structural modules within alginate lyase by truncating an endo-type alginate lyase into two successive catalytic modules. The effects of module deletion on biochemical characteristics and product distributions were further investigated. The N-terminal module (Aly7B-CDI) exhibited no activity toward alginate, polyM or polyG, but the C-terminal module (Aly7B-CDII) retained its activity. The full-length enzyme (Aly7B) and its truncated counterpart (Aly7B-CDII) had similar substrate specificities, but Aly7B-CDII had lower activity. Moreover, the activity of Aly7B was much higher than Aly7B-CDII at 30°C. Aly7B-CDII, however, possessed higher optimal pH and better pH stability than the full-length enzyme. The final degradation products for Aly7B were unsaturated di-, tri- and tetra-oligosaccharides, and those for Aly7B-CDII were unsaturated mono-, di-, tri-, tetra- and penta-oligosaccharides. Therefore, the potential impact of the noncatalytic module Aly7B-CDI on the catalytic module Aly7B-CDII was further elucidated by characterizing Aly7B and its truncations. These data contribute to the functional understanding of these differing modules.