Exploring the response of PACAP on thermal endurance of F-actin by differential scanning calorimetry

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a bioactive peptide known for its diverse effects on the nervous system. While numerous studies have demonstrated the neuroprotective properties of PACAP, its role in tissue regeneration and potential as a therapeutic agent remain to be fully understood. Specifically, the understanding of PACAP's impact on cytoskeletal dynamics, particularly the organization and disorganization of actin filament networks, is limited due to the scarcity of in vitro studies in this area. Additionally, the interaction between PACAP and actin has been minimally explored, and the influence of PACAP on the thermal stability of actin is completely unknown. To address these gaps, the current study aimed to investigate the impact of different forms and fragments of PACAP on the thermal denaturation and renaturation of Ca2+-F-actin using a differential scanning calorimetry (DSC) approach. Our primary objective was to determine whether PACAP modulates the thermal stability of Ca2+-F-actin and establish a temperature-dependent pattern of any structural alterations that may occur as a result of PACAP interaction. Two PACAP forms exist in vivo: the 38 amino acid length PACAP38 and the PACAP27, the latter truncated at the C-terminal. Both in the PACAP38 + Ca2+-F-actin and in the PACAP6-38 + Ca2+-F-actin mixtures, the DSC scans exhibited a significant decrease of actin denaturation temperature compared to the control; however, the PACAP27 + Ca2+-F-actin and PACAP6-27 + Ca2+-F-actin revealed no remarkable differences compared to the actin control sample. The calorimetric enthalpy of the truncated PACAP27 and PACAP6-27 + actin mixture also followed the tendencies mentioned above. Thus, in PACAP27 and PACAP6-27 mixture, there was no change in the denaturation temperature of actin, and no significant Delta Hcal was observed. Through this research, we sought to elucidate the underlying mechanisms of PACAP's effects on actin dynamics using thermal de- and renaturation cycles.