Electrically conductive polymers are promising materials for charge transfer from living cells to the anodes of electrochemical biosensors and biofuel cells. The modification of living cells by polypyrrole (PPy) causes shortened cell lifespan, burdens the replication process, and diminishes renewability in the long term. In this paper, the viability and morphology non-modified, inactivated, and PPy-modified yeasts were evaluated. The results displayed a reduction in cell size, an incremental increase in roughness parameters, and the formation of small structural clusters of polymers on the yeast cells with the increase in the pyrrole concentration used for modification. Yeast modified with the lowest pyrrole concentration showed minimal change; thus, a microbial fuel cell (MFC) was designed using yeast modified by a solution containing 0.05 M pyrrole and compared with the characteristics of an MFC based on non-modified yeast. The maximal generated power of the modified system was 47.12 mW/m², which is 8.32 mW/m² higher than that of the system based on non-modified yeast. The open-circuit potentials of the non-modified and PPy-modified yeast-based cells were 335 mV and 390 mV, respectively. Even though applying a PPy layer to yeast increases the charge-transfer efficiency towards the electrode, the damage done to the cells due to modification with a higher concentration of PPy diminishes the amount of charge transferred, as the current density drops by 846 μA/cm². This decrease suggests that modification by PPy may have a cytotoxic effect that greatly hinders the metabolic activity of yeast.

Neurodegenerative disorders, such as Alzheimer’s and Parkinson’s diseases, are associated with the formation of amyloid fibrils. The DNAJB6b (JB6) chaperone greatly inhibits the disease-related self-assembly of amyloid peptides in an ATP-independent manner. The molecular basis of this process is, however, not understood. Here, we studied the low complexity linker between the N- and C-terminal domains of JB6 as an isolated 110 amino acid residue construct, to get a better understanding of the role of the composition of the intact protein. We investigate the structure and aggregation behaviour of the linker and its anti-amyloid activity in comparison with the full-length chaperone. We find that the linker contains ca. 45% α-helix and 20% β-sheet and is in itself an amyloid-like peptide that self-assembles into different structures, which are bigger than those formed by the intact chaperone, including fibrils. The isolated linker protects against fibril formation of Aβ42 as well as α-synuclein, but is less potent than the intact chaperone. Based on our results, we propose a possible mechanism behind JB6 and linker amyloid suppression relating to their self-assembly behaviour. In the intact protein, the domains serve to solubilize the linker such that the solution concentration of exposed linker is high enough to sustain its high potency against amyloid formation.

The molecular chaperone DNAJB6b inhibits the disease-related self-assembly of amyloid peptides in an efficient and ATP-independent manner. The molecular basis for this action is not yet fully understood, but the low-complexity region of DNAJB6b as a stand-alone peptide displays its antiamyloid formation properties and an ability to form self-assembled structures. Here, we studied the role of phenylalanine residues within the low-complexity region of the intact chaperone to gain insight into the role of these aromatic amino acid residues in chaperone-amyloid interactions. We designed, expressed, purified, and tested eight variants with various numbers of phenylalanine residues within the low-complexity region substituted with either alanine or serine. We show that substituting only 3 of these residues significantly affects the amyloid inhibition activity of the chaperone as well as its self-assembling ability, while substituting more residues affects these functions in a dose-dependent manner. Furthermore, we show that substituting all the phenylalanine residues within the low-complexity region reduces the amyloid inhibition activity of intact DNAJB6b to the equivalent of the isolated C-terminal domain, indicating that most of the chaperone activity stems from the aromatic residues within the low-complexity region.