Phosphorylation, although necessary, may not be sufficient to fully activate many receptor @entity669 kinases (RTKs). Oligomerization-induced conformational changes may be necessary to modulate the kinetic properties of RTKs and render them fully functional. To investigate this regulatory mechanism, recombinant TPR-MET, a functionally active oncoprotein derivative of the RTK @entity1916 , has been expressed and purified for quantitative enzymatic analysis. This naturally occurring oncoprotein contains the cytoplasmic domain of @entity1916 fused to a coiled coil motif from the nuclear pore complex (TPR). cytoMET, the monomeric analog of TPR-MET, has also been expressed and purified for comparative enzymatic analysis. @entity855 and peptide substrates have been kinetically characterized for both TPR-MET and cytoMET. Significantly, phosphorylated TPR-MET has smaller Km values for @entity855 (Km, @entity855 ) and peptide substrates (Km,peptide) and a larger kcat relative to phosphorylated cytoMET. This provides the first direct evidence that receptor oligomerization and not simply activation loop phosphorylation modulates RTK enzymatic activity. The @entity855 dissociation constants (Kd, @entity855 ) for the two enzymes also displayed significant differences. In contrast, the KI values for the @entity855 competitive inhibitor @entity47796 are similar for the two phosphorylated enzymes. These results suggest that much of the oligomerization-induced kinetic changes occur with respect to peptide substrate binding or catalytic efficiency. The possibility that oligomerization-induced conformational changes occur within the cytoplasmic domain of receptor @entity669 kinases has significant implications for structure-based design of RTK inhibitors and the development of a detailed mechanistic model of RTK activation.

Oligomerization-induced modulation of TPR-MET XXXX kinase activity.

@entity669 :: ('CHEBI:18186', 'Chemical') :: ['tyrosine'] @entity47796 :: ('CHEBI:15738', 'Chemical') :: ['staurosporin'] @entity1916 :: ('4233', 'Gene') :: ['c-MET'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP']
@entity669 :: (CHEBI:18186,Chemical) :: ['tyrosine']
