The amino acid residue L113 is involved in arginine kinase activity and structural stability

Arginine kinase (AK) catalyzes the reversible phosphorylation of arginine by ATP, yielding the phosphoarginine. Domain-domain interactions are important to the function of multidomain proteins. However, little is known about the role of the linker in the proteins folding, activity and structural stability. In this research, a series mutation of conserved residue L113 located in the linker was mutated to explore its roles in the activity and structural stability of AK. The mutations L113D and L113K led to pronounced loss of activity and structural stability. Furthermore, spectroscopic experiments indicated that the mutations L113D and L113K impaired the structure of AK, which resulted in a partially unfolded state with more hydrophobic exposure and exposed Trp residues. The inability to fold to the functional compact state made the mutant is prone to aggregate under environmental stresses. While the mutation L113I almost had no effect on AK activity and structural stability. These results suggested that the residue L113 played important roles in sustaining the N- and C-terminal domains interactions.