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Creatine Kinase
Amy Ward
Overview
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Metabolism
Creatine Kinase Isoforms
ATP Recycling
Clinical Relevance
Metabolism
 ATP is the energy currency in the cell
 Cellular respiration occurs in the
mitochondria
 Muscle and brain are most actively
metabolizing tissues
ATP as Energy Source
 ATP donates high energy bond in
coupled reactions
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Substrate
ATP
Product
ADP
ATP Recycling
 Creatine kinase catalyzes transfer of
phosphate from N-phosphoryl creatine
(PCr) to ADP
 Energy homeostasis
PCr
Cr
ADP
ATP
Creatine Kinase
 Crystallization attempts date back to
1950s
 First successful crystal formed in 1996
Creatine Kinase
 Different isoforms depending on location
 Coupled to sites of energy production or
consumption
CK Isoforms
 Cytosolic Isoforms
 Muscle-type
 Brain-type
 Exist as dimers
 Temporal energy buffering
 Mitochondrial Isoforms
 Exist in dimer-octamer equilibrium
 Spatial energy buffering
Cytosolic Isoforms
 Subunits: M and B
 Dimeric isoenzymes in cytosol (85 kDa):
 MM (muscle-type)
 BB (brain-type)
 MB hybrid
Cytosolic Isoforms
 Function as a temporal energy buffer
 ADP + PCr  ATP + Cr
 Coupled to:
 Glycolysis
 Actin-myosin system
 Temporal Energy Buffering
Muscle-Type CK: Monomer
 Small N
domain
 Large C
domain
Muscle-Type CK
Muscle-Type CK: Dimer
 Monomer-monomer
interface site highly
conserved
 All isoenzymes have:
 4 Trp sites
 4 Cys sites
Muscle-Type CK
 MM-CK bound to Mband in myofibril
 Cardiac tissue: 50%
of CK action
Muscle-type CK
 CK maintains high
ATP concentration
Muscle-Type CK
 Mutation in CK genes linked to
myocardial infarction
 Heart diseases linked to low levels of CK
Brain-Type CK
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Structure very similar to Muscle-Type CK
Most tissues contain MB and BB types
High levels in brain, retina, and sperm
BB form is the precursor for the other two
 BB  MB  MM
Brain-Type CK
 CK levels associated with learning
processes
 CK overexpressed in tumours
 Decreased CK  neurodegeneration
Mitochondrial CK
 Bound to outside of inner membrane
within cristae
 Form microcompartments with porins
Mitochondrial CK
 Transphosphorylation
 Cr enters through pore
 Cr + ATP  PCr + ADP
 PCr exits through pore
 PCr mediates between sites of ATP
consumption and production
 Spatial Energy Buffering
Mitochondrial CK
Mi-CK: Structure
Mi-CK: Monomer
 Small (residues 1-112) N-terminal domain
 Large (residues 113-380) C-terminal domain
 ATP binding site located in the cleft between
the two domains
Mi-CK: Dimer
 Trp residues
 Trp 206: monomermonomer contact
 Trp 264 & Nterminal: octamer
forming
Mi-CK: Octamer
 stable against denaturation
 insensitive to proteolysis
 Dissociation to dimer takes hours to
weeks
 Accelerated with addition of transition
state analogue, TSAC = creatine, MgADP & nitrate
Mi-CK: Structure
 Mi-CK fold differs from all other kinases
 Structures of Mi-CK-ATP and free
enzyme very similar
Mi-CK: Structure
 Active site residues:
 Phosphate groups of ATP interact with Arg
residues 125, 127, 287, 315
 Cys278: substrate binding
 His61: mutation impairs enzyme activity
 Loop residues 60-65 moves toward active
site for catalysis
 Trp223: crucial for catalysis
Mi-CK: Octameric
Structure
Mi-CK: Octameric
Structure
ATP Recycling
 The PCr circuit:
 Spatial separation of
ATP consumption
and synthesis
Mitochondrial VS
Cytosolic CK
 Very similar structures and structural
elements
 Mi-CK evolved different folding pattern for
catalyzing phosphoryl transfer
 Allow compartmentalization of function
References
1. Wallimann T et al. 1998. Some new aspects of creatine kinase (CK): compartmentation,
structure, function and regulation for cellular and mitochondrial bioenergetics and
physiology. Biofactors 8, 229-234.
2. Schlattner U et al. 1998. Functional aspects of the X-ray structure of mitochondrial creatine
kinase: A molecular physiology approach. Molecular and Cellular Biochemistry 184, 125140.
3. Yamamichi H et al. 2001. Creatine kinase gene mutation in a patient with muscle creatine
kinase deficiency. Clinical Chemistry 47, 1967-1973.
4. Alberts B et al. 1994. Molecular Biology of the Cell, 3rd edition. New York: Garland Publishing.
5. Lipskaya TY. 2000. The physiological role of the creatine kinase system: evolution of views.
Biochemistry (Moscow) 66, 115-129.