PT  - JOURNAL ARTICLE
AU  - Joseph L. Harman
AU  - Andrea N. Loes
AU  - Gus D. Warren
AU  - Maureen C. Heaphy
AU  - Kirsten J. Lampi
AU  - Michael J. Harms
TI  - Evolution of multifunctionality through a pleiotropic substitution in the innate immune protein S100A9
AID  - 10.1101/865493
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 865493
4099  - http://biorxiv.org/content/early/2019/12/05/865493.short
4100  - http://biorxiv.org/content/early/2019/12/05/865493.full
AB  - Multifunctional proteins are evolutionary puzzles: how do proteins evolve to satisfy multiple functional constraints? S100A9 is one such multifunctional protein. It potently amplifies inflammation via Toll-like receptor 4 and is antimicrobial as part of a heterocomplex with S100A8. These two functions are seemingly regulated by proteolysis: S100A9 is readily degraded, while S100A8/S100A9 is resistant. We take an evolutionary biochemical approach to show that S100A9 evolved both functions and lost proteolytic resistance from a weakly proinflammatory, proteolytically resistant amniote ancestor. We identify a historical substitution that has pleiotropic effects on S100A9 proinflammatory activity and proteolytic resistance but has little effect on S100A8/S100A9 antimicrobial activity. We thus propose that mammals evolved S100A8/S100A9 antimicrobial and S100A9 proinflammatory activities concomitantly with a proteolytic “timer” to selectively regulate S100A9. This highlights how the same mutation can have pleiotropic effects on one functional state of a protein but not another, thus facilitating the evolution of multifunctionality.