Glutamine-Specific N-Terminal Amidase, a Component of the N-End Rule Pathway

SummaryDeamidation of N-terminal Gln by NtQ-amidase, an N-terminal amidohydrolase, is a part of the N-end rule pathway of protein degradation. We detected the activity of NtQ-amidase, termed Ntaq1, in mouse tissues, purified Ntaq1 from bovine brains, identified its gene, and began analyzing this enzyme. Ntaq1 is highly conserved among animals, plants, and some fungi, but its sequence is dissimilar to sequences of other amidases. An earlier mutant in the Drosophila Cg8253 gene that we show here to encode NtQ-amidase has defective long-term memory. Other studies identified protein ligands of the uncharacterized human C8orf32 protein that we show here to be the Ntaq1 NtQ-amidase. Remarkably, “high-throughput” studies have recently solved the crystal structure of C8orf32 (Ntaq1). Our site-directed mutagenesis of Ntaq1 and its crystal structure indicate that the active site and catalytic mechanism of NtQ-amidase are similar to those of transglutaminases.