Homo sapien brain-type creatine kinase

Sydney Buchman '24 and Kod McCune '24

Contents:

I. Introduction

Homo sapiens brain-type creatine kinase is a transferase enzyme and belongs to the phosphagen kinase superfamily, and is the only phosphagen located in vertebrate species.1,2 The kinase is vital for cellular metabolism, and is found in high quantities in the brain and retina of the body. Specifically, the kinase is responsible for the reversible phosphoryl reaction of ATP and creatine. The kinase takes the gamma phosphate group off a bound ATP molecule and transfers to creatine - creating phosphorylated creatine (PCr).1,3 This allows the body to store phosphates on creatine, which prevents excessive buildup of ATP. Such a buildup would inhibit glycolysis and the production of ATP. When in need of ATP, the kinase can then work the reverse reaction and transfer the phosphate back onto ADP, thus producing ATP for cellular activity. The interplay between these two molecules is crucial for energy transport and maintaining energy levels throughout key organs of the body.3

Brain-type creatine kinase provides the necessary ATP for brain function and brain energy metabolism. It has been found that the kinase associates with ATPases, and regulates ion transport crucial for brain functionality.1,4 Due to its importance, deficiencies in creatine kinase levels have been linked to severe neurodegenerative diseases.1,4,5

 

Figure 1: The reaction scheme of the creatine phosphoryl transfer reaction. The phosphate group of ATP is transferred onto creatine, yielding phosphocreatine and ADP as products. The arrow indicates that this reaction is reversible, which is an important feature for bodily function.6

The brain type creatine kinase (hBB-CK) is formed from two isoenzymes, creating a Each monomer within the homodimer is capable of binding to creatine and ADP to perform the phosphoryl transfer reaction. Furthermore, the dimer contains a N-Terminal alpha helical domain, spanning residues 1-100, and a large C-terminal alpha/beta domain present from residues 1,5 These two distinct domains are connected with a linker region that comprises residues These pieces form the overall base structure of the homodimer protein.2 Additionally, residues Asp-54 and Arg-148 act as interface residues, which produce salt bridges and hydrogen bonding to increase the connectivity between the monomers.1,5

The active site of hBB-CK consists of multiple residues. These include Arg132, Arg130, His191, Glu232, Arg236, Cys283, Arg292, and His296. Residues His66, Ile 69, Val72, on the short loop, and Val325 and Asp326 on the long loop are also included.1  

III. Nucleotide Bonding Interactions

When bound to the (in order to facilitate the phosphoryl reaction), the monomers of hBB-CK undergo a conformational change, causing the enzyme to appear asymmetric.1,2 The bound monomer assumes a with the other unliganded protomer retaining an open conformation. The closed form is characterized by the loops of residues 60-70 and 323-332 changing position, where they can be seen moving into the active site of the kinase.1 This has the side effect of moving hydrophobic residues Ile69 and Val325 adjacent to the methyl groups of creatine.

The ADP-Mg2+ complex binds to the active site through a variety of interactions. The ribose of the ADP participates in multiple Water molecule are responsible for linking the adenosine with the carboxylate group of Asp335, as well as the main chain carbonyl oxygens of both Arg292 and Ile188.1 His191 forms a hydrogen bond with the 2'-hydroxyl group of the ribose, and also the main-chain nitrogen of Gly294.1

The phosphates of the ADP interact with the phosphate binding pocket, consisting of residues Arg130, Arg132, Arg236, Arg292, and Arg320. The partake in extensive hydrogen bonding with the oxygens of the phosphate. Specifically, the N-eta-1 on Arg132 and the N-epsilon on Arg292 create monodentate interactions with the beta-phosphate. The Arg130 bonds with the beta-phosphate and the ring-oxygen of the ribose. Arg236 forms a hydrogen bond with the beta-phosphate, and Arg320 with the alpha-phosphate.1 The last two residues (Arg236 and Arg320) form additional hydrogen bonds with nitrate ions incorporated in the transition state of the phosphoryl reaction.1 Mg2+ is also present in this complex, mainly to stabilize the reaction.

IV. Creatine Bonding Interactions

The is bound to hBB-CK through a hydrogen bond, and numerous bonds through water molecules stabilized by side-chains.1 Residues are responsible for generating binding pocket, which has an innate specificity for creatine. Another residue, Cys283, attaches itself to the eta-N nitrogen of creatine. Ser285 pairs with this Cys283 by binding to its backbone carbonyl and hydroxyl. Together, these two residues the creatine and allow for the phosphorylation reaction to occur. Magnesium (Mg2+) Glu232 also assists in this stabilization, with its carboxyl forming a hydrogen bond (bidentate interaction) with the guanidine of creatine.1 This final interaction properly aligns the creatine for catalysis, allowing the reaction to proceed.  

Figure 2: Highlights the transition state of the creatine-phorylation reaction interacting with the active site loops of creatine kinase (green). Magnesium ions (Mg2+) and the nitrate ions help stabilize the reaction by bridging together the creatine and ADP substrates.1

V. Clinical Importance

Brain-type creatine kinase is imperative for optimal brain function. The kinase is responsible for facilitating the reversible phosphorylation of both ADP and creatine. Possessing high levels of creatine kinase means that an organism can effectively manufacture and store phosphorylated creatine, that can later be converted to ATP for cellular activity. In the brain, creatine kinase has been found to be vital for providing ATP for Na+K- ATPase. The ability to increase and decrease ATP levels within a system allows creatine kinase to control the ion channels and transports in brain cells. Research by Aksenov further proves this stipulation.4 It was found that the brains of cadavers with both Alzheimer's and Pick's disease had a severe lack of BB-CK. This was despite there being normal levels of other variants of creatine kinase in the body. Both these diseases occur when brain cells lose their ability to function, and eventually atrophy and die. Other neurological diseases such as schizophrenia, epilepsy, and even psychosis have been linked to a deficiency in brain-type creatine kinase, making it an essential protein for brain health.4


VI. References

1 Aksenov, M. Y., Aksenova, M. V., Payne, R. M., Smith, C. D., Markesbery, W. R., and Carney, J. M. (1997). The expression of creatine kinase isoenzymes in neocortex of patients with neurodegenerative disorders: Alzheimer's and Pick's disease. Experimental neurology, 146(2), 458-465.

2 Bong, S. M., Moon, J. H., Nam, K. H., Lee, K. S., Chi, Y. M., and Hwang, K. Y. (2008). Structural studies of human brain-type creatine kinase complexed with the ADP-Mg2+-NO3- -creatine transition-state analogue complex. FEBS letters, 582(28), 3959-3965.

3 Michael, E., et al. "Crystal structure of brain-type creatine kinase at 1.41 A resolution." Protein Science 8.11 (1999): 2258-2269.

4 Hornemann, T., Rutishauser, D., and Wallimann, T. "Why is creatine kinase a dimer? Evidence for cooperativity between the two subunits." Biochimica et Biophysica Acta (BBA)-Protein Structure and Molecular Enzymology 1480.1-2 (2000): 365-373. .

5 McLeish, M. J., and Kenyon, G. L. (2005). Relating structure to mechanism in creatine kinase. Critical reviews in biochemistry and molecular biology, 40(1), 1-20.

6 McLaughlin, K., "Creatine Kinase- the definitive guide"Biology Dictionary (2022).

Back to Top