Investigating a back door mechanism of actin phosphate release by steered molecular dynamics
✍ Scribed by Willy Wriggers; Klaus Schulten
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 591 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0887-3585
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✦ Synopsis
In actin-based cell motility, phosphate (P i ) release after ATP hydrolysis is an essential biochemical process, but the actual pathway of P i separation from actin is not well understood. We report a series of molecular dynamics simulations that induce the dissociation of P i from actin. After cleavage from ATP, the singly protonated phosphate (HPO 4 2؊ ) rotates about the ADP-associated Ca 2؉ ion, turning away from the negatively charged ADP towards the putative exit near His73. To reveal the microscopic processes underlying the release of P i , adhesion forces were measured when pulling the substrate out of its binding pocket. The results suggest that the separation from the divalent cation is the rate-limiting step in P i release. Protonation of HPO 4 2؊ to H 2 PO 4؊ lowers the electrostatic barrier during P i liberation from the ion. The simulations revealed a propensity of charged His73 ؉ to form a salt bridge with HPO 4 2؊ , but not with H 2 PO 4 ؊ . His73 stabilizes HPO 4 2؊ and, thereby, inhibits rapid P i release from actin. Arg177 remains attached to P i along the putative back door pathway, suggesting a shuttle function that facilitates the transport of P i to a binding site on the protein surface.