Proteomic analysis on Aspergillus strains that are useful for industrial enzyme production

A simple intracellular proteomic study was conducted to investigate the biological activities of Aspergillus niger during industrial enzyme production. A strain actively secreting a heterologous enzyme was compared to a reference strain. In total, 1824 spots on 2-D gels were analyzed using MALDI-TOF MS, yielding 343 proteins. The elevated levels of UPR components, BipA, PDI, and calnexin, and proteins related to ERAD and ROS reduction, were observed in the enzyme-producer. The results suggest the occurrence of these responses in the enzyme-producers. Major glycolytic enzymes, Fba1, EnoA, and GpdA, were abundant but at a reduced level relative to the reference, indicating a potential repression of the glycolytic pathway. Interestingly, it was observed that a portion of over-expressed heterologous enzyme accumulated inside the cells and digested during fermentation, suggesting the secretion capacity of the strain was not enough for completing secretion. Newly identified conserved-proteins, likely in signal transduction, and other proteins were also investigated. Abbreviations: 2-D: two-dimensional; UPR: unfolded protein response; ER: endoplasmic reticulum; ERAD: ER-associated protein degradation; PDI: protein disulfide-isomerase; ROS: reactive oxygen species; RESS: Repression under Secretion Stress; CSAP: Conserved Small Abundant Protein; TCTP: translationally controlled tumor protein.