title: An unusual organelle in Cryptococcus neoformans links luminal pH and capsule biosynthesis.
abstract: Cryptococcus neoformans is a basidiomycete that causes deadly infections in the immunocompromised. We previously generated a secretion mutant in this fungus by introducing a mutation in the SAV1 gene, which encodes a homolog of the Sec4/Rab8 subfamily GTPases. Under restrictive conditions there are two notable morphological changes in the sav1 mutant: accumulation of post-Golgi vesicles and the appearance of an unusual organelle, which we term the sav1 body (SB). The SB is an electron-transparent structure 0.2-1microm in diameter, with vesicles or other membranous structures associated with the perimeter. Surprisingly, the SB was heavily labeled with anti-glucuronoxylomannan (GXM) antibodies, suggesting that it contains a secreted capsule component, GXM. A structure similar to the SB, also labeled by anti-GXM antibodies, was induced in wild type cells treated with the vacuolar-ATPase inhibitor, bafilomycin A(1). Bafilomycin A(1) and other agents that increase intraluminal pH also inhibited capsule polysaccharide shedding and capsule growth. These studies highlight an unusual organelle observed in C. neoformans with a potential role in polysaccharide synthesis, and a link between luminal pH and GXM biosynthesis.
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Aki
authors.initials: A
authors.lastname: Yoneda
authors.forename: Tamara L
authors.initials: TL
authors.lastname: Doering
mesh_terms: D016667:Bacterial Capsules / Q000096:biosynthesis* / Q000187:drug effects; D001426:Bacterial Proteins / Q000378:metabolism; D020126:Brefeldin A / Q000494:pharmacology; D003455:Cryptococcus neoformans / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D018942:Macrolides / Q000494:pharmacology; D046529:Microscopy, Electron, Transmission; D015388:Organelles / Q000378:metabolism / Q000648:ultrastructure; D011134:Polysaccharides / Q000378:metabolism; D055571:Secretory Pathway / Q000187:drug effects
chemical_list: D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D018942:Macrolides; D011134:Polysaccharides; D020126:Brefeldin A; C027478:glucuronoxylomannan; C040929:bafilomycin A1; D020558:GTP Phosphohydrolases