Characterization of the second and third steps in the enzymatic pathway for microcystin-RR biodegradation by Sphingopyxis sp. USTB-05.

Microcystin-RR (MC-RR) is a dominant variant of microcystin (MC) worldwide. We previously isolated Sphingopyxis sp. USTB-05, which can efficiently biodegrade MC-RR. At least three enzymes encoded by MC-degrading genes are involved. Based on the successful expression of the first gene USTB- 05- A, the second ( USTB- 05- B, KC513423) and third ( USTB- 05- C, KC573527) genes involved in the biodegradation of MC-RR were further cloned from Sphingopyxis sp. USTB-05 and expressed in Escherichia coli BL21 (DE3). After purification, the MC-degrading enzymes encoded by these genes were used for the catalytic degradation of MC-RR. The results demonstrated that the second enzyme encoded by USTB- 05- B could convert linear MC-RR to a tetrapeptide by breaking the Ala-Arg bond. The third enzyme encoded by USTB- 05- C could cleave Adda-Glu peptide bonds of both linear MC-RR and the tetrapeptide of Adda-Glu-Mdha-Ala, producing Adda as their common product. These findings will help better understand the biodegradation mechanism of MCs by Sphingopyxis sp. USTB-05. [ABSTRACT FROM AUTHOR]