The structure of scytonemin, an ultraviolet sunscreen pigment from the sheaths of cyanobacteria

Abstract

Despite knowledge of the existence of the pigment called scytonemin for over 100 years, its structure has remained unsolved until now. This pigment, the first shown to be an effective, photo-stable ultraviolet shield in prokaryotes, is a novel dimeric molecule (molec. wt. 544) of indolic and phenolic subunits and is known only from the sheaths enclosing the cells of cyanobacteria. It is probable that scytonemin is formed from a condensation of tryptophan- and phenylpropanoid-derived subunits. The linkage between these units is unique among natural products and this novel ring structure is here termed the 'scytoneman skeleton'. Scytonemin absorbs strongly and broadly in the spectral region 325-425 nm (UV-A-violet-blue, with an in vivo maximum at 370 nm). However, there is also major absorption in the UV-C (lambda max = 250 nm) and UV-B (280-320 nm). The pigment has been recently shown to provide significant protection to cyanobacteria against damage by ultraviolet radiation. The pigment occurs in all phylogenetic lines of sheathed cyanobacteria and possibly represents a UV screening strategy far more ancient than that of plant flavonoids and animal melanins. How diverse organisms deal with UV radiation is considered of vital importance to global ecology.

Cyanobacterial defense mechanisms against foreign DNA transfer and their impact on genetic engineering

“…In addition to that, the slime is known to house metabolites such as the UV protective Scytonemin (Proteau et al, 1993) and non-covalently attached proteins of mostly unknown function, including nonspecific extracellular nucleases that degrade foreign DNA (Wolk and Kraus 1982, Soper and Reddy 1994, Takahashi et al, 1996. Reduction of EPS production by either optimizing growth conditions or establishing degradation protocols is expected to reduce the CPS layer thickness and help to overcome the physical barrier for DNA import.…”

Chemical mediation of interactions among marine organisms

“…7 ' 46 " 47 These and other UV-absorbing molecules such as scytonemin, 48 " 49 and possibly even brown algal phlorotannins 50 illustrate the variety of roles that natural products play in marine organisms.…”

Chemical Mediation of Interactions Among Marine Organisms

“…7 ' 46 " 47 These and other UV-absorbing molecules such as scytonemin, 48 " 49 and possibly even brown algal phlorotannins 50 illustrate the variety of roles that natural products play in marine organisms.…”

“…and the major metabolite 7-deacetoxyolepupuane 48 both caused necrosis in Cacospongia when they were incorporated into agar strips and placed in contact with Cacospongia for 7 days. In addition to its 48 role in competition, 7-deacetoxyolepupuane 48 deterred feeding by natural assemblages of reef fishes as well as a spongivorous angelfish, illustrating the multiple ecological roles that a single secondary metabolite may play. 215 Engel and Pawlik 237 tested extracts of 20 Caribbean sponges in Florida for their ability to deter overgrowth by 3 sponges in field assays.…”