Abstract
Choline kinase alpha is a 457-residue protein that catalyzes the reaction between ATP and choline to yield ADP and phosphocholine. This metabolic action has been well studied because of choline kinase’s link to cancer malignancy and poor patient prognosis. As the myriad of x-ray crystal structures available for this enzyme show, chemotherapeutic drug design has centered on stopping the catalytic activity of choline kinase and reducing the downstream metabolites it produces. Furthermore, these crystal structures only reveal the catalytic domain of the protein, residues 80–457. However, recent studies provide evidence for a non-catalytic protein-binding role for choline kinase alpha. Here, we show that choline kinase alpha interacts with the SH3 domain of c-Src. Co-precipitation assays, surface plasmon resonance, and crystallographic analysis of a 1.5 Å structure demonstrate that this interaction is specific and is mediated by the poly-proline region found N-terminal to the catalytic domain of choline kinase. Taken together, these data offer strong evidence that choline kinase alpha has a heretofore underappreciated role in protein-protein interactions, which offers an exciting new way to approach drug development against this cancer-enhancing protein.
Highlights
Choline kinase alpha is a 457-residue protein that catalyzes the reaction between ATP and choline to yield ADP and phosphocholine
Co-precipitation assays, surface plasmon resonance, and crystallographic analysis of a 1.5 Å structure demonstrate that this interaction is specific and is mediated by the poly-proline region found N-terminal to the catalytic domain of choline kinase
X-ray crystal structures have provided important insight into the substrate binding sites present in ChoKα. Though such studies have greatly advanced the mechanistic understanding of enzyme catalysis, they show that only residues 80–457 are ordered in the protein (Fig. 1A)
Summary
Choline kinase alpha is a 457-residue protein that catalyzes the reaction between ATP and choline to yield ADP and phosphocholine. As the myriad of x-ray crystal structures available for this enzyme show, chemotherapeutic drug design has centered on stopping the catalytic activity of choline kinase and reducing the downstream metabolites it produces These crystal structures only reveal the catalytic domain of the protein, residues 80–457. Co-precipitation assays, surface plasmon resonance, and crystallographic analysis of a 1.5 Å structure demonstrate that this interaction is specific and is mediated by the poly-proline region found N-terminal to the catalytic domain of choline kinase Taken together, these data offer strong evidence that choline kinase alpha has a heretofore underappreciated role in protein-protein interactions, which offers an exciting new way to approach drug development against this cancer-enhancing protein. Choline kinase is the enzyme responsible for the conversion of choline (Cho) to phosphocholine (pCho) via the transfer of the gamma-phosphoryl group of ATP1. Many structures exist demonstrating how inhibitors bind to ChoKα, and several generations of drug candidates have been developed to inhibit this clinically relevant enzyme[12,13,14]
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