LLP1 is a pyrophosphatase involved in homeostasis/quality control of dolichol-linked oligosaccharide

Dolichol-linked oligosaccharide (DLO) is the precursor for asparagine (N)-linked protein glycosylation. DLO synthesis can be impaired by genetic and environmental factors, leading to the accumulation of various immature DLO intermediates that are subsequently cleaved into phosphorylated oligosaccharides (POSs). Despite the fact that its activity has been known since the 1970s, the identity of the enzyme has not been clarified. Here, we identified a Saccharomyces cerevisiae gene encoding a DLO-pyrophosphatase (Llp1), which converts DLO to POSs. Intriguingly, LLP1 mRNA was translated through a programmed +1 translational frameshifting. LLP1 orthologs encode members of VanZ family proteins, which are found in various bacteria and fungi. Llp1 and its substrate DLO are likely to be localized in the Golgi, and when LLP1 was knocked out, abnormal DLO modified by Golgi mannosyltransferases accumulated, which is consistent with a role in DLO homeostasis/quality control. This study provides insights into how the cellular levels and quality of DLOs are maintained in eukaryotes.