Complexation of Lysozyme with Sodium Poly(styrenesulfonate)
via the Two-State and Non-Two-State Unfoldings of Lysozyme
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Abstract
To
provide an in-depth understanding of the complexation mechanism
of protein and polyelectrolyte, a heating–cooling–reheating
protocol was employed to study the unfolding and refolding behaviors
of a model protein, lysozyme, in the presence of a negatively charged
polyelectrolyte, sodium poly(styrenesulfonate) (PSS). It was found
that, with elevated PSS concentration, a new state (state I) was first
formed via a “two-state” conversion process and this
state could further convert to a completely unfolded state (state
II) via a “non-two-state” conversion. This non-two-state
conversion process occurs without the coexistence of states I and
II but involves the formation of various intermediate unfolded protein
structures. Different from the pure lysozyme that exhibited refolding
upon cooling from its heat-denatured state, lysozyme in state I could
undergo unfolding upon heating but no refolding upon cooling, while
lysozyme in state II did not undergo unfolding or refolding upon thermal
treatments. In addition, the effects of ionic strength and molecular
weight of polyelectrolyte on the unfolding and refolding behaviors
of lysozyme were also investigated. The present work provides a better
understanding of the principles governing protein–polyelectrolyte
interactions and may have implications for the fabrication of biocolloids
and biofilms