Tk-SP N-propeptide domain
This is the N-propeptide domain found in Tk-SP, a subtilisin-like serine protease from Thermococcus kodakaraensis. The beta sheet of this domain packs tightly to the two nearly parallel alpha helices 2 and 3 located at the surface of the subtilisin domain. Gln105 and Asp107 of the N-propeptide domain also bind to the N-termini of these two alpha-helices to form helix caps.
Jiyao W et al.(2023). "The conserved domain database in 2023.",