Regulation of Aspergillus nidulans CreA-Mediated Catabolite Repression by the F-Box Proteins Fbx23 and Fbx47

Autor(es)

de Assis, Leandro Jose ; Ulas, Mevlut ; Annick Ries, Laure Nicolas ; El Ramli, Nadia Ali Mohamed ; Sarikaya-Bayram, Ozlem ; Braus, Gerhard H. ; Bayram, Ozgur ; Goldman, Gustavo Henrique

• Tipo de documento: Artigo Científico
• Fonte: MBIO; v. 9, n. 3, p. 19-pg., 2018-05-01.

Resumo

The attachment of one or more ubiquitin molecules by SCF (Skp-Cullin-F-box) complexes to protein substrates targets them for subsequent degradation by the 26S proteasome, allowing the control of numerous cellular processes. Glucose-mediated signaling and subsequent carbon catabolite repression (CCR) are processes relying on the functional regulation of target proteins, ultimately controlling the utilization of this carbon source. In the filamentous fungus Aspergillus nidulans, CCR is mediated by the transcription factor CreA, which modulates the expression of genes encoding biotechnologically relevant enzymes. Although CreA-mediated repression of target genes has been extensively studied, less is known about the regulatory pathways governing CCR and this work aimed at further unravelling these events. The Fbx23 F-box protein was identified as being involved in CCR and the Delta fbx23 mutant presented impaired xylanase production under repressing (glucose) and derepressing (xylan) conditions. Mass spectrometry showed that Fbx23 is part of an SCF ubiquitin ligase complex that is bridged via the GskA protein kinase to the CreA-SsnF-RcoA repressor complex, resulting in the degradation of the latter under derepressing conditions. Upon the addition of glucose, CreA dissociates from the ubiquitin ligase complex and is transported into the nucleus. Furthermore, casein kinase is important for CreA function during glucose signaling, although the exact role of phosphorylation in CCR remains to be determined. In summary, this study unraveled novel mechanistic details underlying CreA-mediated CCR and provided a solid basis for studying additional factors involved in carbon source utilization which could prove useful for biotechnological applications. IMPORTANCE The production of biofuels from plant biomass has gained interest in recent years as an environmentally friendly alternative to production from petroleum-based energy sources. Filamentous fungi, which naturally thrive on decaying plant matter, are of particular interest for this process due to their ability to secrete enzymes required for the deconstruction of lignocellulosic material. A major drawback in fungal hydrolytic enzyme production is the repression of the corresponding genes in the presence of glucose, a process known as carbon catabolite repression (CCR). This report provides previously unknown mechanistic insights into CCR through elucidating part of the protein-protein interaction regulatory system that governs the CreA transcriptional regulator in the reference organism Aspergillus nidulans in the presence of glucose and the biotechnologically relevant plant polysaccharide xylan. (AU)

• Processo FAPESP: 14/00789-6 - Caracterização funcional de fosfatases de Aspergillus nidulans envolvidas no metabolismo da glicose
• Beneficiário: Leandro Jose de Assis
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 16/07870-9 - A influência de proteínas quinases ativadas por mitógenos (MAPK) na expressão de determinantes genéticos importantes para a virulência de Aspergillus fumigatus
• Beneficiário: Gustavo Henrique Goldman
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 16/03900-0 - Identificação de interações proteicas na regulação da repressão catabólica do carbono em Aspergillus nidulans
• Beneficiário: Leandro Jose de Assis
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Pós-Doutorado