title: Drosophila Dystroglycan is a target of O-mannosyltransferase activity of two protein O-mannosyltransferases, Rotated Abdomen and Twisted.
abstract: Recent studies highlighted an emerging possibility of using Drosophila as a model system for investigating the mechanisms of human congenital muscular dystrophies, called dystroglycanopathies, resulting from the abnormal glycosylation of alpha-dystroglycan. Several of these diseases are associated with defects in O-mannosylation, one of the most prominent types of alpha-dystroglycan glycosylation mediated by two protein O-mannosyltransferases. Drosophila appears to possess homologs of all essential components of the mammalian dystroglycan-mediated pathway; however, the glycosylation of Drosophila Dystroglycan (DG) has not yet been explored. In this study, we characterized the glycosylation of Drosophila DG using a combination of glycosidase treatments, lectin blots, trypsin digestion, and mass spectrometry analyses. Our results demonstrated that DG extracellular domain is O-mannosylated in vivo. We found that the concurrent in vivo activity of the two Drosophila protein O-mannosyltransferases, Rotated Abdomen and Twisted, is required for O-mannosylation of DG. While our experiments unambiguously determined some O-mannose sites far outside of the mucin-type domain of DG, they also provided evidence that DG bears a significant amount of O-mannosylation within its central region including the mucin-type domain, and that O-mannose can compete with O-GalNAc glycosylation of DG. We found that Rotated Abdomen and Twisted could potentiate in vivo the dominant-negative effect of DG extracellular domain expression on crossvein development, which suggests that O-mannosylation can modulate the ligand-binding activity of DG. Taken together these results demonstrated that O-mannosylation of Dystroglycan is an evolutionarily ancient mechanism conserved between Drosophila and humans, suggesting that Drosophila can be a suitable model system for studying molecular and genetic mechanisms underlying human dystroglycanopathies.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Naosuke
authors.initials: N
authors.lastname: Nakamura
authors.forename: Stephanie H
authors.initials: SH
authors.lastname: Stalnaker
authors.forename: Dmitry
authors.initials: D
authors.lastname: Lyalin
authors.forename: Olga
authors.initials: O
authors.lastname: Lavrova
authors.forename: Lance
authors.initials: L
authors.lastname: Wells
authors.forename: Vladsilav M
authors.initials: VM
authors.lastname: Panin
mesh_terms: D000818:Animals; D004330:Drosophila / Q000201:enzymology* / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D049030:Dystroglycans / Q000737:chemistry / Q000378:metabolism*; D008364:Mannosyltransferases / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry
chemical_list: C550355:Dg protein, Drosophila; D029721:Drosophila Proteins; D049030:Dystroglycans; D008364:Mannosyltransferases; C550353:rt protein, Drosophila; C550354:tw protein, Drosophila; C082696:protein O-mannosyltransferase