Biophysical Characterization of the C-Terminal Tail of T. rubrum PacC Reveals an Inherent Intrinsically Disordered Structure with pH- Induced Structural

PacC is a key transcriptional regulator of human pathogenic fungus Trichophyton rubrum with pivotal roles in pH homeostasis and virulence. We report the first biophysical characterization of the C-terminal inhibitory tail of PacC, pertinent to its physiological role in maintaining the inactive state of PacC at acidic pH which undergoes conformational changes for its proteolytic removal and activation, at alkaline pH. To gain insights into the structural features of PacC that enable the required conformational flexibility, we performed gel filtration chromatog-raphy, dynamic light scattering, circular dichroism, and 1-anilino-8-naphthalenesulfonate binding and showed that the tail exhibits properties similar to intrinsically disordered proteins, as also predicted by bioinformatics tools. We demonstrate that the C -terminal tail is conformationally flexible and attains a molten globule-like state at extremely acidic pH and undergoes biphasic GdmCl-induced unfolding in a noncooperative manner with an intermediate X state. We hypothesize that the conformational plasticity of the C-terminal tail of PacC may play a significant role in modulating its pH-dependent transcriptional activation.

Automated summary

PacC is a key transcriptional regulator of Trichophyton rubrum, a human pathogenic fungus. The C-terminal inhibitory tail of PacC plays a crucial role in maintaining its inactive state at acidic pH and undergoes conformational changes for its activation at alkaline pH. The tail exhibits properties similar to intrinsically disordered proteins and may play a significant role in modulating the pH-dependent transcriptional activation of PacC.