Intermediates in the refolding of urea-denatured dimeric arginine kinase from Stichopus japonicus

Mutation of the conserved G66 residue in GS region decreased structural stability and activity of arginine kinase

Arginine kinase (AK) catalyzes the reversible phosphorylation of arginine by ATP, yielding the phosphoarginine. Amino acid residues in the guanidine specificity (GS) region play important roles in the guanidine-recognition. However, little is known about roles of amino acid residue G66 in the GS region in proteins folding, activity and structural stability. In this study, a series of G66 mutations were constructed to investigate its roles in AK's structural stability and activity. Our studies revealed that mutations in this conserved site could cause pronounced loss of activity, conformational changes and structural stability. Spectroscopic experiments indicate that G66 mutations influences AK transition from the molten globule intermediate to the native state in folding process. These results provided herein may suggest that amino acid residue G66 may play a relatively important role in AK's activity and structural stability.

Biodegradable polymeric gene delivering nanoscale hybrid micelles enhance the suppression effect of LRIG1 in breast cancer

Biodegradable polymeric gene delivering nanoscale hybrid micelles enhance the suppression effect of LRIG1 in breast cancer.

Impact of inter-subunit interactions on the dimeric arginine kinase activity and structural stability

Arginine kinase (AK) is a key enzyme for cellular energy metabolism, catalyzing the reversible phosphoryl transfer from phosphoarginine to ADP in invertebrates. In this study, the inter-subunit hydrogen bonds between the Q53 and D200 and between D57 and D200 were disrupted to explore their roles in the activity and structural stability of Stichopus japonicus (S. japonicus) AK. Mutating Q53 and/or D57 to alanine (A) can cause pronounced loss of activity and substrate synergism, and cause distinct conformational changes. Spectroscopic experiments indicated that mutations destroying the inter-subunit hydrogen bonds impaired the structure of dimer AK, and resulted in a partially unfolded state. The inability to fold to the functional compact state made the mutants prone to be inactivated and aggregate under environmental stresses. Restoring hydrogen bonds in Q53E and D57E mutants could rescue the loss of activity and substrate synergism, and conformational changes. All those results suggested that the inter-subunit interactions played a key role in keeping the activity, substrate synergism and structural stability of dimer AK. The result herein may provide a clue in understanding the folding and self-assembly processes of oligomeric proteins.

Zinc induces unfolding and aggregation of dimeric arginine kinase by trapping reversible unfolding intermediate

Arginine kinase plays an important role in the cellular energy metabolism of invertebrates. Dimeric arginine kinase (dAK) is unique in some marine invertebrates. The effects of Zn²(+) on the unfolding and aggregation of dAK from the sea cucumber Stichopus japonicus were investigated. Our results indicated that Zn²(+) caused dAK inactivation accompanied by conformational unfolding, the exposure of hydrophobic surface, and aggregation. Kinetic studies showed the inactivation and unfolding of dAK followed biphasic kinetic courses. Zn²(+) can affect unfolding and refolding of dAK by trapping the reversible intermediate. Our study provides important information regarding the effect of Zn²(+) on metabolic enzymes in marine invertebrates.