Data Sheet 1_The protein kinases family in fungi: adaptability, virulence and conservation between species.docx

Protein Kinases (PKs) are a large family of enzymes that act as “molecular switches,” playing fundamental role in cellular signaling through protein phosphorylation. This process consists in transfer a phosphate group (γ-PO₄2−) from ATP (adenosine triphosphate) to specific residues in target proteins; thereby, controlling vital cellular processes, such as (i) cell proliferation and differentiation, (ii) response to environmental stimuli (stress, nutrients, hormones), (iii) metabolism, (iv) cell cycle and apoptosis, and (v) signal transduction. Among fungi, adaptability is intrinsically connected to their ability to thrive under extreme environmental stress, being morphological plasticity an example of this adaptability. While many of these adaptive responses are regulated by diverse signaling pathways involving different kinase families, as mitogen-activated protein kinase (MAPK) for example, this review places a special focus on the General Control Nonderepressible 2 kinase (GCN2), a highly conserved sensor of amino acid scarcity in many fungi, as well as the species Cryptococcus neoformans, Candida albicans, and Aspergillus fumigatus. Amino acid deprivation triggers the accumulation of uncharged tRNAs, which directly activate GCN2, and this activation leads to the phosphorylation of the eukaryotic initiation factor 2 alpha (eIF2α) at the serine in the position 51, initiating the Integrated Stress Response (ISR). Phosphorylated eIF2α suppresses global translation initiation while selectively enhancing the translation of stress-responsive genes, notably GCN4, which encodes a transcription factor that promotes amino acid biosynthesis and stress adaptation. In Cryptococcus neoformans, GCN2 emerges as the sole kinase responsible for eIF2α phosphorylation, a unique role in modulating translational responses to environmental and host-induced stressors. Previous studies have shown that the absence of GCN2 disrupts eIF2α phosphorylation, impairing stress responses and reducing pathogenicity, therefore being an important target for development of new generation antifungals. To better understand the mechanistic role of GCN2 and related kinases in amino acid sensing and stress response, we present a review based on studying the central role of kinases in fungal stress adaptation, discussing how the high conservation of their catalytic kinase domains makes them valuable as phylogenetic markers and therapeutic targets.

蛋白激酶（Protein Kinases，PKs）是一类庞大的酶家族，充当“分子开关”，通过蛋白质磷酸化在细胞信号传导中发挥核心作用。该过程指将三磷酸腺苷（adenosine triphosphate，ATP）上的磷酸基团（γ-PO₄²⁻）转移至靶蛋白的特定残基，借此调控诸多关键细胞进程，包括：(i) 细胞增殖与分化；(ii) 对环境刺激（压力、营养物质、激素）的响应；(iii) 新陈代谢；(iv) 细胞周期与细胞凋亡；以及(v) 信号转导。在真菌界中，适应性与其在极端环境压力下存活的能力内在相关，形态可塑性便是这类适应性的典型例证。尽管诸多此类适应性响应由涉及不同激酶家族的多样信号通路调控，例如丝裂原活化蛋白激酶（mitogen-activated protein kinase，MAPK），本综述重点关注通用控制非阻遏2激酶（General Control Nonderepressible 2 kinase，GCN2）——一种在多数真菌中高度保守的氨基酸匮乏感应器——以及新型隐球菌（Cryptococcus neoformans）、白色念珠菌（Candida albicans）和烟曲霉（Aspergillus fumigatus）这三个物种。氨基酸剥夺会引发不带负载的转运RNA（uncharged tRNA）积累，后者可直接激活GCN2；该激活过程会使真核翻译起始因子2α（eukaryotic initiation factor 2 alpha，eIF2α）的第51位丝氨酸发生磷酸化，进而启动整合应激反应（Integrated Stress Response，ISR）。磷酸化的eIF2α会抑制全局性翻译起始，同时选择性增强应激响应基因的翻译，其中尤以GCN4为重：GCN4编码一种可促进氨基酸生物合成与应激适应性的转录因子。在新型隐球菌中，GCN2是唯一负责eIF2α磷酸化的激酶，其在调控针对环境与宿主诱导应激源的翻译响应方面发挥着独特作用。既往研究表明，敲除GCN2会破坏eIF2α的磷酸化过程，损害应激响应能力并降低致病性，因此GCN2是开发新一代抗真菌药物的重要靶点。为更深入阐明GCN2及其相关激酶在氨基酸感知与应激响应中的机制性作用，本综述围绕激酶在真菌应激适应性中的核心作用展开探讨，分析其催化激酶结构域的高度保守性如何使其成为系统发育标记与治疗靶点的宝贵价值。