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Selenomelanin: An Abiotic Selenium Analogue of Pheomelanin
journal contribution
posted on 2020-07-07, 14:34 authored by Wei Cao, Naneki C. McCallum, Qing Zhe Ni, Weiyao Li, Hannah Boyce, Haochuan Mao, Xuhao Zhou, Hao Sun, Matthew P. Thompson, Claudia Battistella, Michael R. Wasielewski, Ali Dhinojwala, Matthew D. Shawkey, Michael D. Burkart, Zheng Wang, Nathan C. GianneschiMelanins are a family
of heterogeneous biopolymers found ubiquitously
across plant, animal, bacterial, and fungal kingdoms where they act
variously as pigments and as radiation protection agents. There exist
five multifunctional yet structurally and biosynthetically incompletely
understood varieties of melanin: eumelanin, neuromelanin, pyomelanin,
allomelanin, and pheomelanin. Although eumelanin and allomelanin have
been the focus of most radiation protection studies to date, some
research suggests that pheomelanin has a better absorption coefficient
for X-rays than eumelanin. We reasoned that if a selenium enriched
melanin existed, it would be a better X-ray protector than the sulfur-containing
pheomelanin because the X-ray absorption coefficient is proportional
to the fourth power of the atomic number (Z). Notably, selenium is
an essential micronutrient, with the amino acid selenocysteine being
genetically encoded in 25 natural human proteins. Therefore, we hypothesize
that selenomelanin exists in nature, where it provides superior ionizing
radiation protection to organisms compared to known melanins. Here
we introduce this novel selenium analogue of pheomelanin through chemical
and biosynthetic routes using selenocystine as a feedstock. The resulting
selenomelanin is a structural mimic of pheomelanin. We found selenomelanin
effectively prevented neonatal human epidermal keratinocytes (NHEK)
from G2/M phase arrest under high-dose X-ray irradiation. Provocatively,
this beneficial role of selenomelanin points to it as a sixth variety
of yet to be discovered natural melanin.
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Keywords
radiation protectionhigh-dose X-ray irradiationallomelaninradiation protection agentsselenomelanin pointsnovel selenium analogueX-ray protectorvarietysulfur-containing pheomelaninX-ray absorption coefficientbiosynthetic routesradiation protection studieseumelaninabsorption coefficientPheomelanin MelaninsAbiotic Selenium Analogueacid selenocysteineNHEKepidermal keratinocytes
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