Serine proteases are known for their diversified biological
activities. They are involved in immune responses, cellular
differentiation, digestion, complement activation, haemostasis,
etc. The presence of serine proteases in the salivary
secretions of coleoids might suggest for a digestive and/or
prey envenoming role through proteolysis. Using the
nucleotide and complementary protein-level selection analyses,
we detected as many as 26 episodically adaptive sites in
coleoid serine proteases that were accumulating rapid
mutations (Table 3 and Supplementary Table 5; Figs. 6
and 7). These variations could enable these aquatic predators
to feed on a diverse variety of prey types. In snakes and
bees, serine proteases are known to prevent blood coagulation
in the bite-victim, through fibrin(ogen)olysis, enabling
the rapid spread of other venom components through the
blood stream. Serine proteases could thus perform a similar
role in coleoids by preventing the coagulation of the blood
and enhancing the effects of other venom components.