1. The Neurospora peptide:N-glycanase ortholog PNG1 is essential for cell polarity despite its lack of enzymatic activity.
- Author
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Maerz S, Funakoshi Y, Negishi Y, Suzuki T, and Seiler S
- Subjects
- Acetylglucosamine metabolism, Catalytic Domain, Cell Wall enzymology, DNA Repair Enzymes genetics, DNA Repair Enzymes metabolism, Enzyme Activation physiology, Fungal Proteins genetics, Glycosylation, Molecular Sequence Data, Mutagenesis, Neurospora crassa genetics, Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase genetics, Cell Polarity physiology, Fungal Proteins metabolism, Hyphae enzymology, Neurospora crassa enzymology, Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase metabolism
- Abstract
Secretory proteins are subjected to a stringent endoplasmic reticulum-based quality control system that distinguishes aberrant from correctly folded proteins. The cytoplasmic peptide:N-glycanase cleaves oligosaccharides from misfolded glycoproteins and prepares them for degradation by the 26 S proteasome. In contrast to abundant in vitro data on its enzymatic function, the in vivo relevance of peptide:N-glycanase activity remains unclear. Here we show that the PNG1 ortholog from the filamentous ascomycete Neurospora crassa is an essential protein, and its deletion results in strong polarity defects. PNG1 and its predicted binding partner RAD23 have distinct functions in N. crassa and are involved in cell wall integrity and DNA repair, respectively. Moreover, wild type PNG1 has substitutions in essential catalytic amino acids, and its deglycosylation activity is lost. These substitutions are conserved in many PNG1 orthologs of the fungal kingdom, implying a so far unrecognized enzyme-independent function of PNG1 that may only become apparent in highly polar cells such as fungal hyphae.
- Published
- 2010
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