Tandem duplication of serpin genes yields functional variation and snake venom inhibitors

Tandem duplication of genes can play a critical role in the evolution of functional novelty, but our understanding is limited concerning gene duplication's role in coevolution between species. Much is known about the evolution and function of tandemly duplicated snake venom genes, however the potential of gene duplication to fuel venom resistance within prey species is poorly understood. In this study, we characterize patterns of gene duplication of the SERPINA subfamily of genes across in vertebrates and experimentally characterize functional variation in the SERPINA3-like paralogs of a wild rodent. We find the hallmarks of rapid birth-death evolution of SERPINA1-like and SERPINA3-like genes within and between rodent lineages. Next, we recombinantly expressed the 2 paralogous duplicates of SERPINA1 and 12 paralogous duplicates of SERPINA3 found in the genome of the big-eared woodrat (Neotoma macrotis), a species known to be resistant to protease-rich rattlesnake venoms. We found that two SERPINA3 paralogs inhibit snake venom serine proteases, indicating that these proteins have potential as resistance factors in SERPIN-mediated venom resistance. In addition, functional variation is apparent among paralogs, including neofunctionalization to inhibit both chymotrypsin-like and and trypsin-like proteases simultaneously for one venom-inhibiting paralog. Our results provide further evidence that the rapid evolution of SERPINA1 and SERPINA3 gene copy number across rodents has adaptive potential by producing functionally-diverse inhibitors.