title: Despite its high similarity with monomeric arginine kinase, muscle creatine kinase is only enzymatically active as a dimer.
abstract: Although having highly similar primary to tertiary structures, the different guanidino kinases exhibit distinct quaternary structures: monomer, dimer or octamer. However, no evidence for communication between subunits has yet been provided, and reasons for these different levels of quaternary complexity that can be observed from invertebrate to mammalian guanidino kinases remain elusive. Muscle creatine kinase is a dimer and disruption of the interface between subunits has been shown to give rise to destabilized monomers with slight residual activity; this low activity could, however, be due to a fraction of protein molecules present as dimer. CK monomer/monomer interface involves electrostatic interactions and increasing salt concentrations unfold and inactivate this enzyme. NaCl and guanidine hydrochloride show a synergistic unfolding effect and, whatever the respective concentrations of these compounds, inactivation is associated with a dissociation of the dimer. Using an interface mutant (W210Y), protein concentration dependence of the NaCl-induced unfolding profile indicates that the active dimer is in equilibrium with an inactive monomeric state. Although highly similar to muscle CK, horse shoe crab (Limulus polyphemus) arginine kinase (AK) is enzymatically active as a monomer. Indeed, high ionic strengths that can monomerize and inactivate CK, have no effect on AK enzymatic activity or on its structure as judged from intrinsic fluorescence data. Our results indicate that expression of muscle creatine kinase catalytic activity is dependent on its dimeric state which is required for a proper stabilization of the monomers.
authors.affiliation: Université Claude Bernard Lyon 1, UMR CNRS 5013 Bâtiment Chevreul, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
authors.forename: Ayman M
authors.initials: AM
authors.lastname: Awama
authors.forename: Hortense
authors.initials: H
authors.lastname: Mazon
authors.forename: Christian
authors.initials: C
authors.lastname: Vial
authors.forename: Olivier
authors.initials: O
authors.lastname: Marcillat
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001122:Arginine Kinase / Q000737:chemistry / Q000378:metabolism; D002850:Chromatography, Gel; D052283:Creatine Kinase, MM Form / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D019791:Guanidine / Q000494:pharmacology; D006737:Horseshoe Crabs / Q000201:enzymology; D009132:Muscles / Q000201:enzymology*; D011489:Protein Denaturation; D017510:Protein Folding; D020836:Protein Structure, Quaternary / Q000187:drug effects; D021122:Protein Subunits; D011817:Rabbits; D012965:Sodium Chloride / Q000494:pharmacology; D040681:Structural Homology, Protein
chemical_list: D021122:Protein Subunits; D012965:Sodium Chloride; D052283:Creatine Kinase, MM Form; D001122:Arginine Kinase; D019791:Guanidine