GO:0044572 [4Fe-4S] cluster assembly: Mechanism, Genes

Iron-sulfur (Fe-S) clusters are ancient, versatile cofactors that are indispensable for numerous cellular processes, including electron transfer, catalysis, and gene regulation. Among them, the [4Fe-4S] cluster is a particularly common and functionally diverse form, consisting of four iron and four sulfur atoms arranged in a cubic geometry. The biological process dedicated to the incorporation of these atoms into a cluster is defined by the Gene Ontology term GO:0044572, [4Fe-4S] cluster assembly. This process is not a spontaneous event but is tightly orchestrated by complex protein machineries, primarily located in the mitochondria of eukaryotic cells. Understanding the molecular details of [4Fe-4S] cluster assembly is fundamental to deciphering how cells maintain iron homeostasis, respond to oxidative stress, and execute essential metabolic pathways [1,5]. Research over the past decades has revealed that defects in [4Fe-4S] cluster assembly are associated with a growing list of human pathologies, ranging from mitochondrial myopathies to cancer and neurodegeneration [1,7]. The assembly process involves a series of steps: iron and sulfur are first mobilized and combined on scaffold proteins to form a transient cluster, which is then transferred to carrier proteins and finally inserted into target apoproteins [1,2]. Each step requires specific protein factors, and their dysfunction can lead to disease [1,7]. Moreover, the process is highly sensitive to environmental insults, such as copper overload, which can impair cluster assembly and contribute to toxicity. For researchers, GO:0044572 represents a focal point for studying cellular iron metabolism, mitochondrial function, and the mechanisms of related diseases [1,7]. The advent of CRISPR gene editing has revolutionized the ability to create precise cellular and animal models to investigate the roles of individual genes in this pathway [1,3]. This article provides a comprehensive overview of [4Fe-4S] cluster assembly, covering its definition, key genes, regulatory mechanisms, disease connections, and the state-of-the-art methods used to study it, with a focus on how CRISPR-based models can accelerate discovery.

GO:0044572, [4Fe-4S] cluster assembly, is the biological process responsible for the incorporation of four iron atoms and four sulfur atoms into an iron-sulfur cluster. This process is a subset of iron-sulfur cluster assembly and is specifically dedicated to the formation of the [4Fe-4S] cluster type, as opposed to other cluster types like [2Fe-2S]. The term encompasses the biochemical steps and the protein machinery required to build the cluster from its elemental components, ensuring that the cluster is correctly assembled and delivered to target proteins [1,2].

[4Fe-4S] cluster assembly is fundamentally important because [4Fe-4S] clusters are essential cofactors for a wide array of proteins involved in critical cellular processes, including oxidative phosphorylation, DNA repair, ribosome biogenesis, and metabolism [1,6]. Without proper assembly, these proteins lose their function, leading to cellular energy failure, genomic instability, and metabolic collapse. In humans, mutations in genes encoding the assembly machinery cause severe multi-systemic diseases, often with neurological and muscular symptoms. Furthermore, the assembly process is a target of environmental toxins and is implicated in the pathophysiology of common diseases such as cancer and ischemia-reperfusion injury [5,7]. Therefore, studying [4Fe-4S] cluster assembly is not only a basic science endeavor but also a clinically relevant pursuit that can inform therapeutic strategies.

The following table lists key genes and proteins involved in [4Fe-4S] cluster assembly, along with their major roles and relevance to research.

The process of [4Fe-4S] cluster assembly is regulated at multiple levels to meet cellular demands and respond to stress. Key regulatory nodes include the availability of iron and sulfur, the expression of assembly machinery genes, and the activity of transcription factors such as the iron-responsive element-binding proteins (IRPs) that control iron uptake and storage. In mitochondria, the assembly process is coupled to the respiratory chain activity and the redox state of the cell. Copper has been shown to impair [4Fe-4S] cluster assembly, suggesting a regulatory role for metal homeostasis. Additionally, the assembly of specific clusters can be regulated by the target apoprotein levels, ensuring that clusters are only made when needed. Post-translational modifications of assembly factors, such as phosphorylation, may also modulate their activity, although the details are still emerging.

Mutations in genes encoding the [4Fe-4S] cluster assembly machinery, such as ISCU, ISCA1, ISCA2, NFU1, BOLA3, and IBA57, cause severe mitochondrial diseases often presenting with myopathy, encephalopathy, and developmental delay. These disorders highlight the critical role of [4Fe-4S] clusters in energy metabolism and neuronal function. For example, ISCU mutations lead to a myopathy with exercise intolerance, while NFU1 mutations cause a fatal multiple mitochondrial dysfunctions syndrome. The study of these diseases has been instrumental in understanding the assembly pathway and its tissue-specific requirements.

Iron overload can exacerbate renal ischemia-reperfusion injury by promoting tubular cuproptosis, a form of cell death triggered by copper, through interrupting the function of LIAS, a [4Fe-4S] cluster-dependent enzyme. This links [4Fe-4S] cluster assembly to acute kidney injury and metal-induced cell death. The study by Chen et al. (2025) demonstrated that iron overload disrupts LIAS function, leading to cuproptosis and worsened injury, suggesting that targeting [4Fe-4S] cluster assembly could be therapeutic.

The [4Fe-4S] cluster of Mak16 is required for its function in ribosome biogenesis, and disruption of this cluster impairs ribosome assembly. This connects [4Fe-4S] cluster assembly to ribosomopathies, a group of diseases caused by defective ribosome biogenesis. The study by Duppe et al. (2025) showed that the [4Fe-4S] cluster of Mak16 is essential for its role in ribosome biogenesis, providing a direct link between cluster assembly and translation. This expands the disease relevance of [4Fe-4S] cluster assembly beyond mitochondrial disorders.

Cancer cells often exhibit altered iron metabolism and depend on [4Fe-4S] cluster assembly for proliferation and survival. The assembly machinery is upregulated in some cancers, and targeting it can induce cell death. For instance, the [4Fe-4S] cluster assembly pathway is essential for the function of enzymes involved in DNA replication and repair, making it a potential vulnerability in cancer. However, more research is needed to fully understand the role of [4Fe-4S] cluster assembly in cancer and to develop specific inhibitors.

Biochemical assays, such as those measuring the reconstitution of [4Fe-4S] clusters on apo-proteins, are fundamental for studying assembly [3,4]. Spectroscopic techniques like UV-visible absorption, electron paramagnetic resonance (EPR), and circular dichroism (CD) are used to characterize cluster formation and integrity [3,4]. These methods allow researchers to monitor the transfer of clusters between proteins and to determine the stoichiometry and redox state of the cluster.

CRISPR-Cas9 genome editing enables the creation of knockout, point mutation, and knock-in cell models to study the function of genes involved in [4Fe-4S] cluster assembly [1,3]. Knockout models reveal essentiality and phenotypic consequences, while point mutations can dissect specific residues involved in cluster binding or transfer. Knock-in of tagged versions of assembly proteins allows for affinity purification and interaction studies. These genetic tools are complemented by RNAi and overexpression strategies.

Affinity purification coupled with mass spectrometry (AP-MS) can identify protein-protein interactions within the [4Fe-4S] cluster assembly machinery. Proximity labeling techniques, such as BioID, can map the interactome of assembly factors in living cells. These methods help to define the network of proteins involved in cluster assembly and transfer, and can reveal disease-relevant interactions.

Fluorescence microscopy with targeted biosensors can monitor iron and sulfur availability in live cells. Mitochondrial function can be assessed using Seahorse respirometry and fluorescent dyes for membrane potential and ROS. These cellular assays provide a physiological context for understanding how [4Fe-4S] cluster assembly defects impact cellular metabolism and viability.

Researchers studying [4Fe-4S] cluster assembly-related genes often need to determine whether a candidate gene is causally involved in the pathway, how mutations affect function, and whether targeting the gene can modulate disease phenotypes. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research, from generating knockout and point-mutation cell models to performing high-throughput library screens and bioinformatics analysis.

[4Fe-4S] cluster assembly (GO:0044572) is a fundamental biological process that underpins the function of numerous essential proteins. Its machinery is highly conserved and tightly regulated, and its dysfunction leads to a spectrum of human diseases. Continued research using advanced CRISPR models and biochemical methods will further illuminate the mechanisms of cluster assembly and provide opportunities for therapeutic intervention. EDITGENE is committed to supporting this research with state-of-the-art gene editing and screening services.