The Tribbles 2 (TRB2) pseudokinase binds to ATP and autophosphorylates in a metal-independent manner

The human Tribbles (TRB)-related pseudokinases are CAMK-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 this 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 Lys 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’ TRB2 mutant can be targeted with specific bulky ligands of the pyrazolo-pyrimidine 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...
Source: BJ Signal - Category: Biochemistry Authors: Tags: BJ Signal Source Type: research