Crystal structure of brain-type creatine kinase at 1.41 A resolution

Energy metabolism in excitable tissues relies on rapid ATP regeneration. Creatine kinase (CK) plays a central role in this process by catalyzing the reversible transfer of phosphate from phosphocreatine to ADP. CK exists in multiple isoforms, each adapted to specific tissues and subcellular compartments. These isoforms are linked to various pathologies, including cancer and neurodegenerative diseases. Despite the clinical relevance, the structural details of CK isoforms remain incomplete. Previous studies have provided lower-resolution structures, but the precise molecular mechanisms of isoform-specific behavior are still unclear. The brain-type CK (BB-CK) is particularly important in neuronal energy homeostasis. However, its structural features at high resolution have not been fully characterized. This lack of detailed structural information limits the ability to design experiments that explore isoform-specific properties. Understanding the structural basis of CK function is essential for connecting enzyme behavior to physiological outcomes. The absence of high-resolution data for BB-CK has hindered progress in this area. This gap motivated the current investigation into the crystal structure of BB-CK at an improved resolution.

The goal of this research was to determine the crystal structure of chicken cytosolic brain-type creatine kinase (BB-CK) at high resolution. This isoform is critical for maintaining energy balance in the brain and other excitable tissues. The study aimed to provide a structural foundation for understanding isoform-specific properties of CK. A high-resolution structure would allow for more accurate modeling of enzyme dynamics and interactions. The researchers focused on BB-CK due to its relevance in neurodegenerative and age-related diseases. The structure could also inform the design of experiments on CK's functional interactions with other proteins. The study sought to clarify the structural differences between CK isoforms. By solving the structure at 1.41 A resolution, the researchers aimed to improve the accuracy of structural models in the guanidino kinase family.

The researchers used molecular replacement to solve the crystal structure of chicken BB-CK. The structure was determined at 1.41 A resolution, which is among the highest for guanidino kinases. The crystallographic data were collected and processed to obtain a detailed atomic model. The structure includes two monomers in the biological dimer, with the exception of the N-terminal region. The team analyzed the structural similarity between the two monomers and compared them to other CK isoforms. Specific Ca2+-mediated interactions were identified between dimers in the asymmetric unit. These interactions resulted in structurally distinct heterodimers with different N-terminal conformations. The high-resolution data enabled the modeling of a putative transition state conformation of BB-CK.

The crystal structure of BB-CK was solved at 1.41 A resolution, offering the most accurate model in the guanidino kinase family. The two monomers in the dimer are nearly identical, except for the N-terminal region. The structure closely resembles other known CK isoforms but shows distinct features in the N-terminal domain. Ca2+ ions mediate interactions between dimers in the asymmetric unit, leading to heterodimeric structures. These heterodimers differ in their N-terminal conformation and secondary structure. The high-resolution data allowed the researchers to model a putative transition state of BB-CK. This model suggests a rigid body movement of the N-terminal domain by 4 A from the substrate-free state. The structural findings provide a basis for understanding isoform-specific properties of CK.

The high-resolution structure of BB-CK provides new insights into the structural diversity of CK isoforms. The structural differences in the N-terminal region may explain isoform-specific functional properties. The Ca2+-mediated interactions observed in the asymmetric unit suggest a role in dimer stability and conformational changes. The transition state model of BB-CK is based on the structural similarity to arginine kinase. This model supports the hypothesis of a rigid body movement of the N-terminal domain during catalysis. The structural data will assist in designing experiments to explore CK's interactions with other proteins. The findings highlight the importance of high-resolution structures in understanding enzyme function. The study contributes to the broader effort to connect CK structure with its physiological roles.