Photosynthetic Production of Sunscreen Shinorine Using an Engineered Cyanobacterium.

Mycosporine-like amino acids (MAAs) are secondary metabolites of a variety of marine organisms including cyanobacteria and macroalgae. These compounds have strong ultraviolet (UV) absorption maxima between 310 and 362 nm and are biological sunscreens for counteracting the damaging effects of UV radiation in nature. The common MAA shinorine has been used as one key active ingredient of environmentally friendly sunscreen creams. Commercially used shinorine is isolated from one red algae that is generally harvested from the wild. Here, we describe the use of Synechocystis sp. PCC6803 as a host for the heterologous production of shinorine. We mined a shinorine gene cluster from the filamentous cyanobacterium Fischerella sp. PCC9339. When expressing the cluster in Synechocystis sp. PCC6803, we observed the production of shinorine using LC-MS analysis, but its productivity was three times lower than the native producer. Integrated transcriptional and metabolic profiling identified rate-limiting steps in the heterologous production of shinorine. The use of multiple promoters led to a 10-fold increase of its yield to 2.37 ± 0.21 mg/g dry biomass weight, comparable to commercially used shinorine producer. The UV protection of shinorine was further confirmed using the engineered Synechocystis sp. PCC6803. This work was the first time to demonstrate the photosynthetic overproduction of MAA. The results suggest that Synechocystis sp. PCC6803 can have broad applications as the synthetic biology chassis to produce other cyanobacterial natural products, expediting the translation of genomes into chemicals.

Cyanobacterial Sfp-type phosphopantetheinyl transferases functionalize carrier proteins of diverse biosynthetic pathways.

Cyanobacteria produce structurally and functionally diverse polyketides, nonribosomal peptides and their hybrids. Sfp-type phosphopantetheinyl transferases (PPTases) are essential to the production of these compounds via functionalizing carrier proteins (CPs) of biosynthetic megaenzymes. However, cyanobacterial Sfp-type PPTases remain poorly characterized, posing a significant barrier to the exploitation of cyanobacteria for biotechnological and biomedical applications. Herein, we describe the detailed characterization of multiple cyanobacterial Sfp-type PPTases that were rationally selected. Biochemical characterization of these enzymes along with the prototypic enzyme Sfp from Bacillus subtilis demonstrated their varying specificities toward 11 recombinant CPs of different types of biosynthetic pathways from cyanobacterial and Streptomyces strains. Kinetic analysis further indicated that PPTases possess the higher binding affinity and catalytic efficiency toward their cognate CPs in comparison with noncognate substrates. Moreover, when chromosomally replacing the native PPTase gene of Synechocystis sp. PCC6803, two selected cyanobacterial PPTases and Sfp supported the growth of resulted mutants. Cell lysates of the cyanobacterial mutants further functionalized recombinant CP substrates. Collectively, these studies reveal the versatile catalysis of selected cyanobacterial PPTases and provide new tools to synthesize cyanobacterial natural products using in vitro and in vivo synthetic biology approaches.