In situ and real-time interfacial rheology and sum frequency generation studies of pale, soft, and exudative-like myosin's hydrophobic interface behavior explained by energy landscapes theory

To disclose the interfacial behavior of proteins, in situ and in real-time degree information to which proteins maintain their original conformation at hydrophobic interfaces is critical. Based on energy landscapes theory, surface hydrophobicity and conformation flexibility in control (native) and pale, soft, and exudative-like (PSE-like (pre-denatured)) myosin at the hydrophobic interface was investigated. When the myosin concentration was lower than the keypoint concentration (Control: 0.05 mg/mL, PSE: 0.1 mg/mL), increasing myosin concentration improved the interfacial diffusion rate (Kdiff) and penetration rate (Kp) at the oil/water interface. Although PSE myosin was easily adsorbed at the interface due to high surface hydrophobicity, hydrophobic aggregation and poor conformation flexibility led to low Kdiff and rearrangement rate (Kr), respectively. According to the sum frequency generation (SFG) results, the proportion of the lost α-helix structures in PSE myosin (from 18.93% to 16.79%) was lower than that in control myosin (from 86.64% to 74.18%) after 3 h at the lipid/water surface in situ and in real-time. The difference in interfacial behaviors between control and PSE myosin may be rely on energy barriers from metastable PSE myosin and different unfolding pathways on energy landscapes between two proteins, supported by SFG. Macroscopically, confocal laser scanning microscopy and backscattering (BS) profiles results showed that unstable PSE myosin-soybean oil emulsion with poor interfacial behavior had a larger droplet size and a higher negative peak of ΔBS than control emulsion, respectively. These results have crucial implications for the regulation of interfacial behavior and emulsion characteristics in proteins with varied denatured states.