 Pseudokinase

A pseudokinase is a protein kinase-like protein domain that lacks one or more conserved residues usually important for conventional phosphoryl-transfer catalysis. The term identifies an atypical kinase-like structure and sequence; it does not by itself establish that the domain is biologically useless, unable to bind ATP, or incapable of every catalytic reaction. Such domains can regulate other proteins through binding and conformational effects.^[ref]

A systematic biochemical study used thermal-shift measurements to examine nucleotide and ion binding in thirty-one pseudokinase domains. Binding properties differed: many showed no detectable nucleotide binding, while others bound nucleotides with different requirements for divalent ions. The results challenged the shortcut of assigning the same biochemical behavior to every atypical domain.^[ref]

For an assay example, suppose adding ATP reproducibly changes a purified domain's thermal unfolding curve. That supports an interaction under the assay conditions; it does not yet demonstrate transfer of a phosphate group to a substrate. Conversely, detecting phosphorylation in a protein preparation does not establish which protein catalyzed it: a small contaminating protein kinase can matter. Binding and catalytic assays therefore require different controls.^[ref]

The useful question is what the particular pseudokinase does in its molecular context. Sequence-based expectations guide experiments, but measurements must distinguish nucleotide recognition, chemical turnover and downstream signaling.