Expression, purification and crystal structure of a truncated acylpeptide hydrolase from Aeropyrum pernix K1

Acylpeptide hydrolase (APH) catalyzes the N-terminal hydrolysis of Nalpha-acylpeptides to release Nalpha-acylated amino acids. The crystal structure of recombinant APH from the thermophilic archaeon Aeropyrum pernix K1 (apAPH) was reported recently to be at a resolution of 2.1 Angstrom; using X-ray diffraction. A truncated mutant of apAPH that lacks the first short alpha-helix at the N-terminal, apAPH-delta(1-21), was cloned, expressed, characterized and crystallized. Data from biochemical experiments indicate that the optimum temperature of apAPH is decreased by 15 degrees C with the deletion of the N-terminal alpha-helix. However, the enzyme activity at the optimal temperature does not change. It suggests that this N-terminal alpha-helix is essential for thermostability. Here, the crystal structure of apAPH-delta(1-21) has been determined by molecular replacement to 2.5 Angstrom;. A comparison between the two structures suggests a difference in thermostability, and it can be concluded that by adding or deleting a linking structure (located over different domains), the stability or even the activity of an enzyme can be modified.