Abstract
Co- and post-translational amino-terminal processing of proteins is one mechanism by which intracellular proteins can be either protected from or targeted to degradation by the N-end Rule pathway (Bachmair, A., Finley, D., and Varshavsky, A. (1986) Science 234, 179-186). A novel enzyme, protein NH2-terminal asparagine amidohydrolase, which can function in this pathway by potentially directing critical regulatory proteins possessing an amino-terminal asparagine residue formed from the removal of N-acetylmethionine, has recently been purified and characterized (Stewart, A.E., Arfin, S. M., and Bradshaw, R. A. (1994) J. Biol. Chem. 269, 23509-23517). Here, we report the isolation and characterization of a cDNA for porcine protein NH2-terminal asparagine amidohydrolase, which indicates that it is a new type of enzyme, not homologous to any previously identified protein. This provides strong evidence for the importance of regulated protein degradation in cellular functioning.
Highlights
Co- and post-translational amino-terminal processing of proteins is one mechanism by which intracellular proteins can be either protected from or targeted to degradation by the N-end Rule pathway (Bachmair, A, Finley, D., and Varshavsky, A (1986) Science 234, 179186)
A novel enzyme, protein NHll-terminal asparagine amidohydrolase, which can function in this pathway by potentially directing critical regulatory proteins possessing an amino-terminal asparagine residue formed from the removal of N-acetylmethionine, has recently been purified and characterized
From previous studies [5,6,7], it is known that exposure of the penultimate asparagine residue destabilizes proteins, rendering them susceptible to N-end Rule-mediated polyubiquitinylation and degradation by the proteasome
Summary
We report the isolation and characterization of a cDNA for porcine protein NHll-terminal asparagine amidohydrolase, which indicates that it is a new type of enzyme, not homologous to any previously identified protein. This provides strong evidence for the importance of regulated protein degradation in cellular functioning. Some 43 unique (nonspecies-redundant) proteins beginning with the Met-Asnsequence have been identified [4] These proteins are almost exclusively involved in such regulatory functions as transcription, signal transduction, and developmental processes. We describe the cDNA and predicted protein sequence and report the interesting observation that, like its activity, it represents a unique protein, unrelated to any known sequence at a detectable level
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