AK3

AK3 Full Name

adenylate kinase 3

AK3 Introduction

Adenylate Kinase 3 is a protein-coding gene that encodes an enzyme involved in cellular energy metabolism. It is widely expressed across various tissues, with notable presence in cells with high energy demands. As a key metabolic enzyme, it participates in the interconversion of adenine nucleotides, helping to maintain the balance of cellular energy carriers. Its ability to regulate nucleotide levels is critical for supporting essential cellular processes that require energy, making it an integral part of cellular metabolic networks.It has structural motifs that facilitate substrate binding and catalysis, ensuring efficient conversion of adenine nucleotides. These structural traits are essential for its role in maintaining cellular energy balance, allowing it to respond to changing energy demands. The protein's structure also supports post-translational modifications that fine-tune its enzymatic activity, adapting to varying cellular conditions.

Figure 1.The structure of AK3.

Role in Cancer and as a Metabolic Target
AK3 expression is altered in several human cancers, and its upregulation has been associated with tumor progression and poor prognosis in some tumor types. In hepatocellular carcinoma, AK3 expression is significantly elevated compared to adjacent normal liver tissue, and high AK3 expression correlates with larger tumor size, higher tumor grade, and shorter patient survival. AK3 knockdown in liver cancer cell lines reduces cell proliferation, induces apoptosis, and sensitizes cells to chemotherapeutic agents. The mechanism by which AK3 promotes cancer cell survival is thought to involve its role in maintaining the adenylate energy charge and supporting nucleotide biosynthesis. Cancer cells have high rates of proliferation and require large quantities of nucleotides for DNA replication and RNA synthesis. AK3 enhances the production of ADP, which is then phosphorylated to ATP by the electron transport chain or by substrate-level phosphorylation in the mitochondria. The increased ATP production supports the energy demands of cancer cells, while the recycling of AMP through the purine nucleotide cycle provides the bases needed for nucleotide synthesis.

Animal Models of AK3 Deficiency
Animal models of AK3 deficiency have been generated to study the physiological function of the enzyme and to understand the pathogenesis of the associated human disease. The Ak3 knockout mouse is viable and fertile but shows subtle metabolic abnormalities under baseline conditions. When challenged with a high-fat diet or with conditions that increase energy demand, the knockout mice develop hepatic steatosis, glucose intolerance, and reduced exercise capacity. The mitochondria from Ak3 knockout mice show reduced ATP levels, increased AMP levels, and impaired respiratory control ratio, consistent with a defect in energy charge maintenance. In the brain, Ak3 knockout leads to mild mitochondrial dysfunction and increased susceptibility to seizure-inducing agents, recapitulating some features of the human encephalopathy. The relatively mild phenotype of the knockout mouse compared to the severe human disease may reflect differences in the expression of compensatory enzymes, such as AK4, which is also localized to the mitochondria and has overlapping functions with AK3 in some species. Knockdown of AK3 in zebrafish produces a more severe phenotype, with microcephaly, reduced locomotor activity, and early lethality, suggesting that zebrafish are more dependent on AK3 for development. Both the mouse and zebrafish models are being used to test potential therapies, including gene replacement, small molecule activators, and metabolic interventions.

Alternate Names for AK3

AK3; adenylate kinase 3; AK6; FIX; AK3L1; AKL3L; AKL3L1; GTP:AMP phosphotransferase AK3, mitochondrial; adenylate kinase 3 alpha-like 1; GTP:AMP phosphotransferase, mitochondrial; adenylate kinase 6, adenylate kinase 3 like 1;