Further characterization of the role of the mitochondrial high-mobility group box protein in the intracellular redox environment of Aspergillus nidulans

Abstract

zé p fasor 52, Hungary HmbB, a predominantly mitochondrial high-mobility group box (HMGB) protein, of Aspergillus nidulans affects diverse biological activities, such as sterigmatocystin production, the maintenance of mitochondrial DNA copy number, germination of asexual and sexual spores, and protection against oxidative stress agents. We hypothesized that the latter correlates with an unbalanced intracellular redox state, in which case, a not yet fully characterized physiological function could be attributed to this mitochondrial HMGB protein. Here, we studied the intracellular redox environment and oxidative stress tolerance in hmbB + and hmbBD strains under normal and oxidative stress conditions by measuring glutathione redox couple, intracellular reactive oxygen species (ROS) content and ROS-protecting enzyme activities. Our results revealed that the intracellular redox environment is different in hmbBD conidia and mycelia from that of hmbB + , and shed light on the seemingly contradictory difference in the tolerance of hmbBD mycelia to diamide and menadione oxidative stressors.

The role of the Aspergillus nidulans high mobility group B protein HmbA, the orthologue of Saccharomyces cerevisiae Nhp6p

“…As the hmbAΔ conidiospores showed a delay germination compard to the hmbA + control, we started the growth tests by inoculating pre-grown, non-sporulating mycelial discs instead of conidiospores as previously described 29 .…”

Mitochondrial HMG-Box Containing Proteins: From Biochemical Properties to the Roles in Human Diseases

“…An HmgB deletion strain exhibited a decrease in conidial and ascospore viability, probably due to the importance of HmgB in maintaining mtDNA in spores [ 164 ]. Furthermore, it was also shown that HmgB plays a role in cellular protection against oxidative stress agents, although it is possible that this role is associated with its nuclear functions [ 165 ].…”

HMGB proteins are required for sexual development in Aspergillus nidulans

“…This indicates that HmbB may play a role in the structure and function of nuclear chromatin [11]. This hypothesis is further supported by the altered transcription level of numerous nuclear genes in hmbBΔ [11, 16]. Regarding HmbA and HmbC, we have limited knowledge about their function in terms of their physiological roles and transcriptional regulation, however, based on the functions of their yeast homologues, it can be assumed that they modulate the expression of a wide range of genes [10, 14, 17, 18].…”

“…Of these three A . nidulans proteins, the physiological role of the dually localized mitochondrial/nuclear HmbB was previously characterized in details [11, 16]. Deletion of hmbB has pleiotropic effects (S1 Table).…”

“…The hmbBΔ mutant is viable, but displays severe fitness loss due to the drastic reduction in the viability of conidiospores and ascospores (0.4% viable) [11]. Besides its role in spore viability, HmbB is also involved in diverse biological processes such as sugar metabolism during conidia germination, sterigmatocystin production, redox homeostasis or maintaining mitochondrial DNA copy number [11, 16]. The latter correlates with the mitochondrial localization of HmbB, whereas the other functions might be associated with the nuclear localization of the protein.…”