Key result
Amphipols protect SERCA1a from irreversible denaturation while reversibly inhibiting its activity and slowing backward calcium dissociation, likely by damping protein dynamics.
Amphipols protect membrane proteins like SERCA1a against irreversible denaturation but may inhibit activity by damping protein dynamics.
Amphipols may aid membrane protein handling in research; leaves open translation to cardiac SERCA2a or in vivo models.
Amphipols are amphipathic polymers designed to replace or supplement detergents in membrane protein solution studies. Previous work has suggested both advantages and disadvantages to the use of a polyacrylate-based amphipol, A8-35, for studying the sarcoplasmic reticulum Ca2+-ATPase (SERCA1a). We investigated this issue further using a set of four amphipols with different chemical structures. Previous size exclusion chromatography experiments had shown that A8-35 and SERCA1a/A8-35 complexes aggregate under certain conditions. We show here that aggregation can be prevented by omitting calcium from buffers or by using a sulfonated version of A8-35. A8-35 had previously been shown to protect Ca2+-ATPase from irreversible denaturation, while inhibiting its activity in a reversible manner. We show here that the other three amphipols tested also display these properties and that all four amphipols slow down backward calcium dissociation from the nonphosphorylated solubilized enzyme, a priori an unrelated step. As this calcium dissociation involves the opening up of the bundle of transmembrane ATPase segments, the slowing of this process may indicate that multipoint attachment of the polymers to the hydrophobic transmembrane surface damps protein dynamics ("Gulliver" effect). Damping might be the reason why amphipols also simultaneously protect membrane proteins against irreversible denaturation and may inhibit the activity of those of them that display large rearrangements of their transmembrane surface during their catalytic cycle.
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Picard et al. (2006) studied this question. Amphipols was evaluated on Aggregation, denaturation protection, and calcium dissociation. Amphipols protect SERCA1a from irreversible denaturation while reversibly inhibiting its activity and slowing backward calcium dissociation, likely by damping protein dynamics.
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