Atomic view into Plasmodium actin polymerization, ATP hydrolysis, and phosphate release

BioRxiv : the Preprint Server for Biology
Esa-Pekka KumpulaInari Kursula

Abstract

Plasmodium actins form very short filaments and have a non-canonical link between ATP hydrolysis and polymerization. Long filaments are detrimental to the parasites, but the structural factors constraining Plasmodium microfilament lengths are currently unknown. Using high-resolution crystallography, we show that magnesium binding activates the Plasmodium actin I monomer before polymerization by a slight flattening, which is reversed upon phosphate release. A coordinated potassium ion resides in the active site during hydrolysis and leaves together with the phosphate, a process governed by the position of the Arg178/Asp180-containing A-loop. Asp180 interacts with either Lys270 or His74, depending on protonation, while Arg178 links the inner and outer domains. Hence, the A-loop is a switch between stable and non-stable filament conformations. Our data provide a comprehensive model for polymerization, phosphate release, and the inherent instability of parasite microfilaments.

Related Concepts

Actins
Adenosine Triphosphate
Crystallography
Magnesium
Parasites
Inorganic phosphate
Plasmodium
Protein Binding
Extrinsic
Internal

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