Cryptococcus neoformans cryoultramicrotomy and vesicle fractionation reveals an intimate association between membrane lipids and glucuronoxylomannan |
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| Institution: | 1. Laboratorio de Estudos Integrados em Bioquimica Microbiana, Instituto de Microbiologia Professor Paulo de Goes, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941590, Brazil;2. Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941590, Brazil;3. Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA;4. Departments of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA;5. Pasarow Mass Spectrometry Laboratory, Semel Institute for Neuroscience and Human Behavior and the Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA;1. SAAD Centre for Pharmacy and Diabetes, School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, UK;2. Department of Biochemistry, College of Medicine and Health Sciences, United Arab Emirates University, 17666 Al Ain, United Arab Emirates;3. Viral Zoonoses, Emerging and Vector-Borne Infections Group, Institute of Virology, University of Veterinary Medicine, Veterinärplatz 1, A-1210 Vienna, Austria;4. INSERM U-982, PRIMACEN, CNRS, IRIB, University of Rouen, 76821 Mont-Saint-Aignan, France;5. PISSARO, Institute for Research and Innovation in Biomedicine (IRIB) CNRS UMR 6270, University of Rouen, 76821 Mont-Saint-Aignan, France;6. Department of Microbiology and Immunology, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Oman;7. Rare Species Conservatory Foundation, St. Louis, MO 63110, USA;1. Department of Chemistry, North Carolina State University, Raleigh, North Carolina |
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| Abstract: | Cryptococcus neoformans is an encapsulated pathogenic fungus. The cryptococcal capsule is composed of polysaccharides and is necessary for virulence. It has been previously reported that glucuronoxylomannan (GXM), the major capsular component, is synthesized in cytoplasmic compartments and transported to the extracellular space in vesicles, but knowledge on the organelles involved in polysaccharide synthesis and traffic is extremely limited. In this paper we report the GXM distribution in C. neoformans cells sectioned by cryoultramicrotomy and visualized by transmission electron microscopy (TEM) and polysaccharide immunogold staining. Cryosections of fungal cells showed high preservation of intracellular organelles and cell wall structure. Incubation of cryosections with an antibody to GXM revealed that cytoplasmic structures associated to vesicular compartments and reticular membranes are in close proximity to the polysaccharide. GXM was generally found in association with the membrane of intracellular compartments and within different layers of the cell wall. Analysis of extracellular fractions from cryptococcal supernatants by transmission electron microscopy in combination with serologic, chromatographic and spectroscopic methods revealed fractions containing GXM and lipids. These results indicate an intimate association of GXM and lipids in both intracellular and extracellular spaces consistent with polysaccharide synthesis and transport in membrane-associated structures. |
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