Algal Peptides: The Tide is High
With increasing temperatures across much of the globe, there has also been an increase in harmful algal blooms (HABs). Some species come along with a red color, causing the appearance of a “red tide” and, when severe, a prevalence of dead fish can be seen (and smelled) along the shores. Similarly, cyanobacteria are blue-green algae that are found in freshwater. An overgrowth of algae can be a result of several factors such as rise in temperatures and nutrients, such as those from fertilizer runoff and other nitrogen sources. Too much algae and dead zones or areas where oxygen has been depleted can form, as a result of algal decay.1,5
(photo credit: Denise Karounos, 2018)
Among the many toxins that are produced by blue-green algae, several are cyanobacterial peptides, or cyanopeptides. Cyanopeptides are a toxic metabolite of cyanobacteria and comprise over 60 percent of the already identified bioactive compounds. Cyanopeptides can be both cyclic and linear and may have additional post-translational modifications (PTMs). A subcategory, the microcystins, are hexamers with a characteristic 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-dienoic acid (Adda) moiety, with microcystin LR being the most common.2 In the past, researchers discovered that the inhibitors leupeptin, E-64, and pepstatin had no effect on microcystin LR (MC-LR) degradation.3
A new publication in Environmental Science Europe looks at the harmful effects of cyanobacterial toxins, and in particular, those effects on the human gastrointestinal (GI) tract. Upon oral exposure, typically from aquatic activity or drinking water, the cyanotoxins make their way to the intestines and can trigger antigenic compounds which may trigger an inflammatory response. Microcystins inhibit protein phosphatases 1 and 2A through covalent bonding of the Adda moiety and the enzymes catalytic-site Cys residue, this impedes critical cell signaling. MC-LR also triggers inflammatory cytokine production. The resulting chronic inflammation may lead the way to cancer and other inflammatory process diseases.4 Further work is needed in characterization of toxic metabolites, as well as a need exists for reference standards. We invite you to read further in the references below.
- D. Hall, What Exactly Is a Red Tide?¸Smithsonian Ocean.
- E. M.-L. Janssen, Water Research, 151, 488 (2019).
- D. Bourne, et al., Applied and Environmental Microbiology, 62(11), 4086 (1996).
- B. Kubickova et al., Environ Sci Eur, 31, 31 (2019).