Evolutionary analysis of the anti-viral STAT2 gene of primates and rodents: Signature of different stages of an arms race.

STAT2 plays a strategic role in defending viral infection through the signaling cascade involving the immune system initiated after type I interferon release. Many flaviviruses target the inactivation or degradation of STAT2 as a strategy to impair this host's line of defense. Primates are natural reservoirs for a range of disease-causing flaviviruses (e.g., Zika, Dengue, and Yellow Fever virus), while rodents appear less susceptible. We analyzed the STAT2 coding sequence of 28 Rodentia species and 49 Primates species. Original data from 19 Platyrrhini species were sequenced for the SH2 domain of STAT2 and included in the analysis. STAT2 has many sites whose variation can be explained by positive selection, measurement by two methods (PALM indicated 12, MEME 61). Both evolutionary tests significantly marked sites 127, 731, 739, 766, and 780. SH2 is under evolutionary constraint but presents episodic positive selection events within Rodentia: in one of them, a moderately radical change (serine > arginine) at position 638 is found in Peromyscus species, and can be implicated in the difference in susceptibility to flaviviruses within Rodentia. Some other positively selected sites are functional such as 5, 95, 203, 251, 782, and 829. Sites 251 and 287 regulate the signaling mediated by the JAK-STAT2 pathway, while 782 and 829 create a stable tertiary structure of STAT2, facilitating its connection with transcriptional co-activators. Only three positively selected sites, 5, 95, and 203, are recognized members who act on the interface between STAT2 and flaviviruses NS5 protein. We suggested that due to the higher evolutionary rate, rodents are, at this moment, taking some advantage in the battle against infections for some well-known Flaviviridae, in particular when compared to primates. Our results point to dynamics that fit with a molecular evolutionary scenario shaped by a thought-provoking virus-host arms race.