TY - JOUR
T1 - Cations Stiffen Actin Filaments by Adhering a Key Structural Element to Adjacent Subunits
AU - Hocky, Glen M.
AU - Baker, Joseph L.
AU - Bradley, Michael J.
AU - Sinitskiy, Anton V.
AU - De La Cruz, Enrique M.
AU - Voth, Gregory A.
N1 - Funding Information:
We thank members of the Voth and De La Cruz groups for many helpful discussions. This research was supported by Department of Defense Army Research Office (ARO) through a MURI grant, number W911NF1410403, on which G.A.V. and E.M.DLC. are coinvestigators. G.M.H. was previously supported as a Kadanoff-Rice postdoctoral scholar sponsored by the University of Chicago MRSEC NSF DMR-1420709. G.M.H. is currently supported by a Ruth L. Kirschstein National Research Service Award (NIGMS, F32 GM113415- 01). E.M.DLC. and M.J.B. were also supported by NIH Grant R01-GM097348. Computations performed on Midway at the University of Chicago Research Computing Center, and this research is part of the Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (Awards OCI-0725070 and ACI-1238993) and the state of Illinois. Blue Waters is a joint effort of the University of Illinois at Urbana?Champaign and its National Center for Supercomputing Applications. This work was part of the Petascale Multiscale Simulations of Biomolecular Systems PRAC allocation.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/5/26
Y1 - 2016/5/26
N2 - Ions regulate the assembly and mechanical properties of actin filaments. Recent work using structural bioinformatics and site-specific mutagenesis favors the existence of two discrete and specific divalent cation binding sites on actin filaments, positioned in the long axis between actin subunits. Cation binding at one site drives polymerization, while the other modulates filament stiffness and plays a role in filament severing by the regulatory protein, cofilin. Existing structural methods have not been able to resolve filament-associated cations, and so in this work we turn to molecular dynamics simulations to suggest a candidate binding pocket geometry for each site and to elucidate the mechanism by which occupancy of the "stiffness site" affects filament mechanical properties. Incorporating a magnesium ion in the "polymerization site" does not seem to require any large-scale change to an actin subunits conformation. Binding of a magnesium ion in the "stiffness site" adheres the actin DNase-binding loop (D-loop) to its long-axis neighbor, which increases the filament torsional stiffness and bending persistence length. Our analysis shows that bound D-loops occupy a smaller region of accessible conformational space. Cation occupancy buries key conserved residues of the D-loop, restricting accessibility to regulatory proteins and enzymes that target these amino acids.
AB - Ions regulate the assembly and mechanical properties of actin filaments. Recent work using structural bioinformatics and site-specific mutagenesis favors the existence of two discrete and specific divalent cation binding sites on actin filaments, positioned in the long axis between actin subunits. Cation binding at one site drives polymerization, while the other modulates filament stiffness and plays a role in filament severing by the regulatory protein, cofilin. Existing structural methods have not been able to resolve filament-associated cations, and so in this work we turn to molecular dynamics simulations to suggest a candidate binding pocket geometry for each site and to elucidate the mechanism by which occupancy of the "stiffness site" affects filament mechanical properties. Incorporating a magnesium ion in the "polymerization site" does not seem to require any large-scale change to an actin subunits conformation. Binding of a magnesium ion in the "stiffness site" adheres the actin DNase-binding loop (D-loop) to its long-axis neighbor, which increases the filament torsional stiffness and bending persistence length. Our analysis shows that bound D-loops occupy a smaller region of accessible conformational space. Cation occupancy buries key conserved residues of the D-loop, restricting accessibility to regulatory proteins and enzymes that target these amino acids.
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U2 - 10.1021/acs.jpcb.6b02741
DO - 10.1021/acs.jpcb.6b02741
M3 - Article
C2 - 27146246
AN - SCOPUS:84973452053
SN - 1520-6106
VL - 120
SP - 4558
EP - 4567
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 20
ER -