Structural Characteristics of Pneumolysin and Its Domains in a Biomimetic Solution

Pneumolysin (PLY) and its truncated fragments, domains 1–3 (D1–3), and domain 4 (D4), were purified as recombinant proteins after being cloned and over-expressed in Escherichia coli. The three-dimensional structures of these proteins were quantitatively investigated in a biomimetic condition, phosphate buffered saline (PBS) by synchrotron X-ray scattering. X-ray scattering analysis revealed important structural features including structural parameters. PLY was present as a monomeric form in PBS. The monomeric form resembled its crystallographic structure with a discrepancy of only 6.3%, confirming that PLY forms a stable structure and, thus, retains its structure in the crystalline state and even in PBS solution. D4 was also present as a monomeric form, but its structure was very different from that of the corresponding part in the crystallographic PLY structure; the discrepancy was 92.0%. Such a dissimilar structure might originate from a less folded-chain conformation. This result suggested that the str...