An exotype alginate lyase in Sphingomonas sp. A1: overexpression in Escherichia coli, purification, and characterization of alginate lyase IV (A1-IV).

Sphingomonas sp. A1 (strain A1) cells contain three kinds of endotype alginate lyases [A1-I, A1-II, and A1-III], all of which are formed from a common precursor through posttranslational processing. In addition to these lyases, another type of lyase (A1-IV) that acts on oligoalginates exists in the bacterium. A1-IV was overexpressed in Escherichia coli cells through control of its gene under the T7 promoter. The expression level of the enzyme in E. coli cells was 8.6U/L-culture, which was about 270-fold higher than that in strain A1 cells. The enzyme was purified to homogeneity through three steps with an activity yield of 10.9%. The optimal pH and temperature, thermal stability, and mode of action of the purified enzyme were similar to those of the native enzyme from strain A1 cells. A1-IV exolytically degraded oligoalginates, which were produced from alginate through the reaction of A1-I, A1-II, or A1-III, into monosaccharides, indicating that the cooperative actions of these four enzymes cause the complete depolymerization of alginate in strain A1 cells.