Random coil to alpha helix structural shift in the peptide from phospholipase domain of Parvovirus B19 capsid conjugated with the carrier is caused by acidification of the medium

Spectroscopic studies on isolated domains of large proteins and peptides derived from them are complicated because of their tendency to dissolve in aquatic buffers in form of oligomers. Here we demonstrate that conjugation of such peptides with a carrier protein is helpful for studies on the influence of different factors on their secondary structure. Namely, we approved that SK30 peptide from phospholipase A2 domain of Parvovirus B19 capsid conjugated to BSA through N-terminal Cys residue and SMCC linker undergoes random coil to alpha helix transition in the acidic medium mimicking the environment of endolysosome because of His residue protonation. In contrast, unconjugated peptide does not undergo such shift because it forms stable octamers connected by intermolecular beta sheet, as well as the whole isolated phospholipase domain. Obtained results provide evidence on the mechanism of phospholipase domain folding during the acidification of the medium by the way of the formation of contacts between protonated His153 and Asp175, and opens up a perspective of vaccine development, since rabbit polyclonal antibodies against our conjugate, in which the structure of the second alpha helix from the phospholipase A2 domain has been reproduced, can bind epitopes of the complete unique part of VP1 Parvovirus B19 capsid.