Protein Kinase‐Like Non‐Kinases (PKLNKs), commonly known as “pseudokinases”, are homologous to eukaryotic Ser/Thr/Tyr protein kinases (PKs) but lack the crucial aspartate residue in the catalytic loop, indispensable for phosphotransferase activity. Therefore, they are predicted to be “catalytically inactive” enzyme homologs. Analysis of protein‐kinase like sequences from Arabidopsis thaliana led to the identification of more than 120 pseudokinases lacking catalytic aspartate, majority of which are closely related to the plant‐specific receptor‐like kinase family. These pseudokinases engage in different biological processes, enabled by their diverse domain architectures and specific subcellular localizations. Structural comparison of pseudokinases with active and inactive conformations of canonical PKs, belonging to both plant and animal origin, revealed unique structural differences. The currently available crystal structures of pseudokinases show that the loop topologically equivalent to activation segment of PKs adopts a distinct‐folded conformation, packing against the pseudoenzyme core, in contrast to the extended and inhibitory geometries observed for active and inactive states, respectively, of catalytic PKs. Salt‐bridge between ATP‐binding Lys and DFG‐Asp as well as hydrophobic interactions between the conserved nonpolar residue C‐terminal to the equivalent DFG motif and nonpolar residues in C‐helix mediate such a conformation in pseudokinases. This results in enhanced solvent accessibility of the pseudocatalytic loop in pseudokinases that can possibly serve as an interacting surface while associating with other proteins. Specifically, our analysis identified several residues that may be involved in pseudokinase regulation and hints at the repurposing of pseudocatalytic residues to achieve mechanistic control over noncatalytic functions of pseudoenzymes.

中文翻译：

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全基因组和拟南芥基因组中编码的假激酶的结构分析提供了功能上的见解。

蛋白激酶样非激酶（PKLNK），通常称为“假激酶”，与真核Ser / Thr / Tyr蛋白激酶（PKs）同源，但在催化环中缺乏关键的天冬氨酸残基，这对于磷酸转移酶活性是必不可少的。因此，预计它们是“催化惰性”的酶同源物。拟南芥蛋白激酶样序列的分析导致鉴定出120多种缺乏催化天冬氨酸的假激酶，其中大多数与植物特异性受体样激酶家族密切相关。这些假激酶通过其不同的结构域结构和特定的亚细胞定位而参与不同的生物学过程。具有植物和动物起源的典型PK的活性和非活性构象的假激酶的结构比较显示出独特的结构差异。目前可用的假激酶晶体结构表明，与PKs激活片段拓扑相同的环具有明显折叠的构象，堆积在假酶核心上，与催化活性和非活性状态分别观察到的扩展和抑制几何形状相反PK。ATP结合Lys和DFG-Asp之间的盐桥以及等同于DFG基序的保守非极性残基C-末端与C-螺旋中非极性残基之间的疏水相互作用介导了假激酶中的这种构象。这导致假激酶中假催化环的溶剂可及性增强，当与其他蛋白质缔合时，假激酶可能充当相互作用表面。具体而言，我们的分析确定了可能参与假激酶调节的几个残基，并暗示了伪催化残基的重新利用，以实现对假酶非催化功能的机械控制。