Free Glycine Accelerates the Autoproteolytic Activation of Human Asparaginase

SummaryHuman asparaginase 3 (hASNase3), which belongs to the N-terminal nucleophile hydrolase superfamily, is synthesized as a single polypeptide that is devoid of asparaginase activity. Intramolecular autoproteolytic processing releases the amino group of Thr168, a moiety required for catalyzing asparagine hydrolysis. Recombinant hASNase3 purifies as the uncleaved, asparaginase-inactive form and undergoes self-cleavage to the active form at a very slow rate. Here, we show that the free amino acid glycine selectively acts to accelerate hASNase3 cleavage both in vitro and in human cells. Other small amino acids such as alanine, serine, or the substrate asparagine are not capable of promoting autoproteolysis. Crystal structures of hASNase3 in complex with glycine in the uncleaved and cleaved enzyme states reveal the mechanism of glycine-accelerated posttranslational processing and explain why no other amino acid can substitute for glycine.

Graphical AbstractFigure optionsDownload high-quality image (231 K)Download as PowerPoint slideHighlights
► Increased expression of hASNase3 was observed in several tumors, but the relevance is unclear
► Cancer cells have increased glycolytic flux and thus have more glycine but less aspartate
► Glycine activates the asparaginase activity of hASNase3 by promoting self-cleavage
► Thus, glycine may act as a sensor that regulates cellular aspartate concentrations