Brownian dynamics simulations of interactions between aldolase and G- or F-actin

Compartmentation of proteins in cells is important to proper cell function, interactions of F-actin and glycolytic enzymes is one mechanism by which g lycolytic enzymes can compartment. Brownian dynamics (BD) simulations of th e binding of the muscle form of the glycolytic enzyme fructose-1,6-bisphosp hate aldolase (aldolase) to F- or G-actin provide first-encounter snapshots of these interactions. Using x-ray structures of aldolase, G-actin, and th ree-dimensional models of F-actin, the electrostatic potential about each p rotein was predicted by solving the linearized Poisson-Boltzmann equation f or use in BD simulations. The BD simulations provided solution complexes of aldolase with F- or G-actin. All complexes demonstrate the close contacts between oppositely charged regions of the protein surfaces. Positively char ged surface regions of aldolase (residues Lys 13, 27, 288, 293, and 341 and Arg 257) are attracted to the negatively charged amino terminus (Asp 1 and Glu 2 and 4) and other patches (Asp 24, 25, and 363 and Glu 361, 364, 99, and 100) of actin subunits. According to BD results, the most important fac tor for aldolase binding to actin is the quaternary structure of aldolase a nd actin. Two pairs of adjacent aldolase subunits greatly add to the positi ve electrostatic potential of each other creating a region of attraction fo r the negatively charged subdomain 1 of the actin subunit that is exposed t o solvent in the quaternary F-actin structure.