Computational tools and resources for pseudokinase research

Expression, Purification and Biophysical Characterisation of Klebsiella Pneumoniae Protein Adenylyltransferase: A Systematic Integration of Empirical and Computational Modelling Approaches

Infections that are acquired due to a prolonged hospital stay and manifest 2 days following the admission of a patient to a health-care institution can be classified as hospital-acquired infections. Klebsiella pneumoniae (K. pneumoniae) has become a critical pathogen, posing serious concern globally due to the rising incidences of hypervirulent and carbapenem-resistant strains. Glutaredoxin is a redox protein that protects cells from oxidative stress as it associates with glutathione to reduce mixed disulfides. Protein adenylyltransferase (PrAT) is a pseudokinase with a proposed mechanism of transferring an AMP group from ATP to glutaredoxin. Inducing oxidative stress to the bacterium by inhibiting the activity of PrAT is a promising approach to combating its contribution to hospital-acquired infections. Thus, this study aims to overexpress, purify, and analyse the effects of ATP and Mg2+ binding to Klebsiella pneumoniae PrAT (KpPrAT). The pET expression system and nickel affinity chromatography were effective in expressing and purifying KpPrAT. Far-UV CD spectroscopy demonstrates that the protein is predominantly α-helical, even in the presence of Mg2+. Extrinsic fluorescence spectroscopy with ANS indicates the presence of a hydrophobic pocket in the presence of ATP and Mg2+, while mant-ATP studies allude to the potential nucleotide binding ability of KpPrAT. The presence of Mg2+ increases the thermostability of the protein. Isothermal titration calorimetry provides insight into the binding affinity and thermodynamic parameters associated with the binding of ATP to KpPrAT, with or without Mg2+. Conclusively, the presence of Mg2+ induces a conformation in KpPrAT that favours nucleotide binding.

Inactive metallopeptidase homologs: the secret lives of pseudopeptidases

Inactive enzyme homologs, or pseudoenzymes, are proteins, found within most enzyme families, that are incapable of performing catalysis. Rather than catalysis, they are involved in protein-protein interactions, sometimes regulating the activity of their active enzyme cousins, or scaffolding protein complexes. Pseudoenzymes found within metallopeptidase families likewise perform these functions. Pseudoenzymes within the M14 carboxypeptidase family interact with collagens within the extracellular space, while pseudopeptidase members of the M12 "a disintegrin and metalloprotease" (ADAM) family either discard their pseudopeptidase domains as unnecessary for their roles in sperm maturation or utilize surface loops to enable assembly of key complexes at neuronal synapses. Other metallopeptidase families contain pseudopeptidases involved in protein synthesis at the ribosome and protein import into organelles, sometimes using their pseudo-active sites for these interactions. Although the functions of these pseudopeptidases have been challenging to study, ongoing work is teasing out the secret lives of these proteins.

Informatic challenges and advances in illuminating the druggable proteome

The understudied members of the druggable proteomes offer promising prospects for drug discovery efforts. While large-scale initiatives have generated valuable functional information on understudied members of the druggable gene families, translating this information into actionable knowledge for drug discovery requires specialized informatics tools and resources. Here, we review the unique informatics challenges and advances in annotating understudied members of the druggable proteome. We demonstrate the application of statistical evolutionary inference tools, knowledge graph mining approaches, and protein language models in illuminating understudied protein kinases, pseudokinases, and ion channels.

Redefining pseudokinases: A look at the untapped enzymatic potential of pseudokinases

Catalytically inactive kinases, known as pseudokinases, are conserved in all three domains of life. Due to the lack of catalytic residues, pseudokinases are considered to act as allosteric regulators and scaffolding proteins with no enzymatic function. However, since these "dead" kinases are conserved along with their active counterparts, a role for pseudokinases may have been overlooked. In this review, we will discuss the recently characterized pseudokinases Selenoprotein O, Legionella effector SidJ, and the SARS-CoV2 protein nsp12 which catalyze AMPylation, glutamylation, and RNAylation, respectively. These studies provide structural and mechanistic insight into the versatility and diversity of the kinase fold.

Evolutionary and cellular analysis of the 'dark' pseudokinase PSKH2

Pseudokinases, so named because they lack one or more conserved canonical amino acids that define their catalytically active relatives, have evolved a variety of biological functions in both prokaryotic and eukaryotic organisms. Human PSKH2 is closely related to the canonical kinase PSKH1, which maps to the CAMK family of protein kinases. Primates encode PSKH2 in the form of a pseudokinase, which is predicted to be catalytically inactive due to loss of the invariant catalytic Asp residue. Although the biological role(s) of vertebrate PSKH2 proteins remains unclear, we previously identified species-level adaptions in PSKH2 that have led to the appearance of kinase or pseudokinase variants in vertebrate genomes alongside a canonical PSKH1 paralog. In this paper we confirm that, as predicted, PSKH2 lacks detectable protein phosphotransferase activity, and exploit structural informatics, biochemistry and cellular proteomics to begin to characterise vertebrate PSKH2 orthologues. AlphaFold 2-based structural analysis predicts functional roles for both the PSKH2 N- and C-regions that flank the pseudokinase domain core, and cellular truncation analysis confirms that the N-terminal domain, which contains a conserved myristoylation site, is required for both stable human PSKH2 expression and localisation to a membrane-rich subcellular fraction containing mitochondrial proteins. Using mass spectrometry-based proteomics, we confirm that human PSKH2 is part of a cellular mitochondrial protein network, and that its expression is regulated through client-status within the HSP90/Cdc37 molecular chaperone system. HSP90 interactions are mediated through binding to the PSKH2 C-terminal tail, leading us to predict that this region might act as both a cis and trans regulatory element, driving outputs linked to the PSKH2 pseudokinase domain that are important for functional signalling.