Identification of Novel Peptides Originated from Biodegradation of Microcystins Using UHPLC-HRMS/MS: Fid-Bau Portal

Identification of Novel Peptides Originated from Biodegradation of Microcystins Using UHPLC-HRMS/MS

Thenuwara, Sharmila I. / Shrestha, Upasana / Westrick, Judy A. / Huntley, Jason F. / Isailovic, Dragan

Biodegradation of toxic cyanobacterial cyclic peptides microcystins (MCs) by heterotrophic bacteria isolated from freshwater has gained global interest as an eco-friendly approach for water treatment. This study focused on elucidating the structures of MC-LR breakdown products generated by a group of five bacteria previously isolated from Lake Erie. Three isomers of a tetrapeptide NH₂-Adda-Glu-Mdha-Ala-OH (Adda-TetraP-1, 2, and 3) and a cyclic tripeptide NH₂-Adda-Glu-Mdha-OH (Adda-TriP) were identified during the MC-LR degradation process. Of these peptides, only linear Adda-TetraP-1 was described previously. UHPLC-high-resolution (HR)-MS and MS/MS data acquired for tetrapeptides and the tripeptide and their thiol derivatization showed that Adda-TetraP-2, Adda-TetraP-3, and Adda-TriP were cyclic peptides that contained modified Mdha and Adda moieties. The experimental evidence suggests that the Adda amine group of Adda-TetraP-1 underwent intramolecular aza-Michael reaction with the Mdha double bond to form a cyclic tetrapeptide, which appeared in two diastereomeric forms, of which Adda-TetraP-2 was formed faster than Adda-Tetra-P-3. The Mdha-Ala peptide bond of Adda-TetraP-2 appeared to be hydrolyzed by bacteria to form Adda-TriP. Independent of our laboratory cultures, Adda-TetraP-1, 2, and 3 were detected in Lake Erie water during cyanobacterial blooms, and identifying them will assist in elucidating biodegradation pathways of MC congeners and genes relevant to MC degradation.

How Lake Erie microbes degrade microcystins still remains unanswered. This study reports novel peptides formed from the biodegradation of microcystins by Lake Erie bacteria in laboratory cultures and Lake Erie water.