RESUMEN
Glucosamine-6-phosphate synthase (GlcN-6-P synthase) is an essential enzyme involved in cell wall biogenesis that has been proposed as a strategic target for antifungal chemotherapy. Here we describe the cloning and functional characterization of Sporothrix schenckii GFA1 gene which was isolated from a genomic library of the fungus. The gene encodes a predicted protein of 708 amino acids that is homologous to GlcN-6-P synthases from other sources. The recombinant enzyme restored glucosamine prototrophy of the Saccharomyces cerevisiae gfa1 null mutant. Purification and biochemical analysis of the recombinant enzyme revealed some differences from the wild type enzyme, such as improved stability and less sensitivity to UDP-GlcNAc. The sensitivity of the recombinant enzyme to the selective inhibitor FMDP [N(3)-(4-methoxyfumaroyl)-l-2,3-diaminopropanoic acid] and other properties were similar to those previously reported for the wild type enzyme.
Asunto(s)
Proteínas Fúngicas/aislamiento & purificación , Glucosamina/química , Glutamina-Fructosa-6-Fosfato Transaminasa (Isomerizadora)/aislamiento & purificación , Plásmidos/metabolismo , Saccharomyces cerevisiae/genética , Sporothrix/química , Clonación Molecular , Estabilidad de Enzimas , Escherichia coli/genética , Escherichia coli/metabolismo , Fumaratos/química , Proteínas Fúngicas/antagonistas & inhibidores , Proteínas Fúngicas/química , Proteínas Fúngicas/genética , Expresión Génica , Prueba de Complementación Genética , Biblioteca Genómica , Glucosamina/análogos & derivados , Glutamina-Fructosa-6-Fosfato Transaminasa (Isomerizadora)/antagonistas & inhibidores , Glutamina-Fructosa-6-Fosfato Transaminasa (Isomerizadora)/química , Glutamina-Fructosa-6-Fosfato Transaminasa (Isomerizadora)/genética , Cinética , Sistemas de Lectura Abierta , Plásmidos/química , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Saccharomyces cerevisiae/enzimología , Sporothrix/enzimología , beta-Alanina/análogos & derivados , beta-Alanina/químicaRESUMEN
Molecules composed of beta-1,4-linked N-acetylglucosamine (GlcNAc) and deacetylated glucosamine units play key roles as surface constituents of the human pathogenic fungus Cryptococcus neoformans. GlcNAc is the monomeric unit of chitin and chitooligomers, which participate in the connection of capsular polysaccharides to the cryptococcal cell wall. In the present study, we evaluated the role of GlcNAc-containing structures in the assembly of the cryptococcal capsule. The in vivo expression of chitooligomers in C. neoformans varied depending on the infected tissue, as inferred from the differential reactivity of yeast forms to the wheat germ agglutinin (WGA) in infected brain and lungs of rats. Chromatographic and dynamic light-scattering analyses demonstrated that glucuronoxylomannan (GXM), the major cryptococcal capsular component, interacts with chitin and chitooligomers. When added to C. neoformans cultures, chitooligomers formed soluble complexes with GXM and interfered in capsular assembly, as manifested by aberrant capsules with defective connections with the cell wall and no reactivity with a monoclonal antibody to GXM. Cultivation of C. neoformans in the presence of an inhibitor of glucosamine 6-phosphate synthase resulted in altered expression of cell wall chitin. These cells formed capsules that were loosely connected to the cryptococcal wall and contained fibers with decreased diameters and altered monosaccharide composition. These results contribute to our understanding of the role played by chitin and chitooligosaccharides on the cryptococcal capsular structure, broadening the functional activities attributed to GlcNAc-containing structures in this biological system.