The roles of C-terminal loop residues of dimeric arginine kinase from sea cucumber Stichopus japonicus in catalysis, specificity and structure.
Arginine kinase (AK) catalyzes the reversible phosphorylation of arginine by MgATP to form a high-energy compound phosphoarginine (Parg) and MgADP in forward reaction in invertebrates. To detect the different catalytical mechanisms among Stichopus-AK (dimer) and Limulus-AK (monomer) and Torpedo creatine kinase (dimeric CK) and to reveal the structural role of the C-terminal domain loop (C-loop) of dimeric AK, six single-site mutants, E314D, E314Q, E314V, F315A, F315H and F315Y were constructed as well as two multi-site variants, S312R/F315H/V319E (formed by substituting the C-loop of monomeric AK for that of dimeric AK, termed the AAloop) and S312G/E314V/F315D/E317A/S318A/G321S (formed by substituting the C-loop of dimeric CK for that of dimeric AK, termed the ACloop). The AK activity of the three mutants at Glu(314) decreased significantly, from 60- to 500-fold. The ACloop showed only slight AK activity, unlike the same construction in Limulus-AK. In addition, all Phe(315) mutants including the AAloop which retained Glu(314) had modest AK activity (5-84% of the wild type). All the results above suggested that Glu(314) played a more significant role in catalysis in dimeric AK than in the monomer. In addition, ANS profiles indicated that the tolerance of the three Glu(314) mutants to denaturant decreased slightly compared with wild type AK. Though monomeric AK has a His residue at site 315, mutants F315H and the AAloop could not resist any perturbation of denaturant, and the mutants showed a Gibbs free energy of about 2.7kJ/mol lower than wild type AK. Therefore Phe(315) in dimeric AK has a different role from His(315) in monomeric AK. This might contribute to the stabilization of the native conformation, while His(315) in Limulus AK directly binded to the carboxylate of arginine. Taking all the results above together, we suggested a unique mechanism in dimeric AK, different from both monomeric AK and dimeric CK.
Zhang
Jian-wei
JW
Department of Biological Sciences and Biotechnology, School of Life Science and Engineering, Tsinghua University, Beijing 100084, China.
Zhao
Tong-jin
TJ
Wang
Shi-lei
SL
Guo
Qin
Q
Liu
Tao-tao
TT
Zhao
Feng
F
Wang
Xi-cheng
XC
D000595:Amino Acid Sequence; D000818:Animals; D001122:Arginine Kinase / Q000737:chemistry*; D019281:Dimerization; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012616:Sea Cucumbers; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014508:Urea / Q000737:chemistry / Q000494:pharmacology
D014508:Urea; D001122:Arginine Kinase