title: The Tribbles 2 (TRB2) pseudokinase binds to ATP and autophosphorylates in a metal-independent manner.
abstract: The human Tribbles (TRB)-related pseudokinases are CAMK (calcium/calmodulin-dependent protein kinase)-related family members that have evolved a series of highly unusual motifs in the 'pseudocatalytic' domain. In canonical kinases, conserved amino acids bind to divalent metal ions and align ATP prior to efficient phosphoryl-transfer to substrates. However, in pseudokinases, atypical residues give rise to diverse and often unstudied biochemical and structural features that are thought to be central to cellular functions. TRB proteins play a crucial role in multiple signalling networks and overexpression confers cancer phenotypes on human cells, marking TRB pseudokinases out as a novel class of drug target. In the present paper, we report that the human pseudokinase TRB2 retains the ability to both bind and hydrolyse ATP weakly in vitro. Kinase activity is metal-independent and involves a catalytic lysine residue, which is conserved in TRB proteins throughout evolution alongside several unique amino acids in the active site. A similar low level of autophosphorylation is also preserved in the closely related human TRB3. By employing chemical genetics, we establish that the nucleotide-binding site of an 'analogue-sensitive' (AS) TRB2 mutant can be targeted with specific bulky ligands of the pyrazolo-pyrimidine (PP) chemotype. Our analysis confirms that TRB2 retains low levels of ATP binding and/or catalysis that is targetable with small molecules. Given the significant clinical successes associated with targeting of cancer-associated kinases with small molecule inhibitors, it is likely that similar approaches will be useful for further evaluating the TRB pseudokinases, with the translation of this information likely to furnish new leads for drug discovery.
authors.affiliation: *Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, U.K.
authors.forename: Fiona P
authors.initials: FP
authors.lastname: Bailey
authors.affiliation: *Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, U.K.
authors.forename: Dominic P
authors.initials: DP
authors.lastname: Byrne
authors.affiliation: †Institute of Bioinformatics, University of Georgia, Athens, GA 30602, U.S.A.
authors.forename: Krishnadev
authors.initials: K
authors.lastname: Oruganty
authors.affiliation: *Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, U.K.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Eyers
authors.affiliation: ‡Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, UCSF, San Francisco, CA 94158, U.S.A.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Novotny
authors.affiliation: ‡Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, UCSF, San Francisco, CA 94158, U.S.A.
authors.forename: Kevan M
authors.initials: KM
authors.lastname: Shokat
authors.affiliation: †Institute of Bioinformatics, University of Georgia, Athens, GA 30602, U.S.A.
authors.forename: Natarajan
authors.initials: N
authors.lastname: Kannan
authors.affiliation: *Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, U.K.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Eyers
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D055162:Biocatalysis; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020134:Catalytic Domain; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D006801:Humans; D006868:Hydrolysis; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017354:Point Mutation; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D018797:Cell Cycle Proteins; D047908:Intracellular Signaling Peptides and Proteins; D050505:Mutant Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; C474831:TRIB3 protein, human; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C489044:TRIB2 protein, human; D008239:Lysine