The Neurospora peptide:N-glycanase ortholog PNG1 is essential for cell polarity despite its lack of enzymatic activity.
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.
Maerz
Sabine
S
DFG Research Center of Molecular Physiology of the Brain (CMPB), D-37073 Goettingen, Germany.
Funakoshi
Yoko
Y
Negishi
Yuki
Y
Suzuki
Tadashi
T
Seiler
Stephan
S
D000117:Acetylglucosamine / Q000378:metabolism; D020134:Catalytic Domain; D016764:Cell Polarity / Q000502:physiology*; D002473:Cell Wall / Q000201:enzymology; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D025301:Hyphae / Q000201:enzymology*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009492:Neurospora crassa / Q000201:enzymology* / Q000235:genetics; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000235:genetics / Q000378:metabolism*
D005656:Fungal Proteins; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D045643:DNA Repair Enzymes; D000117:Acetylglucosamine