Effects of urban particulate matter on the secondary structure of albumin

Particulate air pollution is an environmental problem recognized as a global public health issue. Although the toxicological effects of environmental particle matter (PM) have been reported, the mechanism underlying the effect of PM on protein conformational changes, which are associated with the development of various diseases, has yet to be elucidated. In this study, we investigated the effect of urban PM on the secondary structure of proteins using bovine serum albumin (BSA). An urban aerosol (CRM28) was used as the original PM (PMO) and washed with acetone to investigate the effect of PM with two different chemical compositions. After washing with acetone, the remaining PM fraction contained decreased amounts of ions and carbon, while the metallic concentration was increased; thus, this PM fraction was labeled as PMM. After incubation of BSA with PM, the samples were subjected to Fourier-transform infrared (FT-IR) spectroscopy to investigate the changes in the absorption peak of the amide I band. BSA incubated with PMO and PMM showed an increase in the β-sheet ratio to the total secondary structure. Furthermore, the β-sheet content was more significantly increased when mixed with PMM (by 22.6%), indicating a more significant effect of the metallic fraction on the formation of β-sheets. In comparison, the lowest total amount of α-helix and β-sheets (with a decrease of 8.5%) was observed after incubation with PMO, associated with the protein partial unfolding in the presence of ions and carbonaceous PM constituents. The potential of a long-term effect of PM composition on protein structure would be of future interest in in vivo time-course studies.