Computer simulations of glycolytic enzyme interactions with F-actin.

Prior research has shown that glycolytic enzymes can associate with F-actin in muscle cells. Established knowledge includes the role of aldolase in glycolysis and its potential interactions with actin. However, the specific mechanism of binding and the influence of actin's N-terminal residues remained unclear. No prior work had resolved the exact contribution of the first four residues of actin to enzyme binding. This gap motivated the use of chemical crosslinking and computational modeling to explore the interaction. The study aimed to clarify how structural differences between muscle and yeast actin affect binding affinity. Experimental findings suggested a higher affinity for muscle actin, but the underlying cause was not fully understood. This uncertainty drove the need for simulations to estimate binding free energy and identify critical residues. The research sought to bridge the gap between structural data and functional implications.

The aim of this study was to investigate the molecular basis of glycolytic enzyme interactions with F-actin using computational and experimental approaches. The specific problem addressed was the role of the actin N-terminus in enzyme binding. The motivation stemmed from prior observations that muscle aldolase and GAPDH bind more strongly to muscle actin than to yeast actin. The researchers proposed to use crosslinking and Brownian dynamics simulations to test this hypothesis. The goal was to determine whether the first four residues of actin influence binding affinity. The study also aimed to compare muscle and yeast actin structures to identify functional differences. By linking aldolase with actin fragments, the team sought to isolate the N-terminal region's contribution. The findings could clarify how actin's structure affects enzyme localization in muscle cells.

The researchers chemically crosslinked muscle actin and aldolase to form an 80 kDa complex. Hydroxylamine digestion produced a 40.5 kDa fragment containing aldolase and the first 12 residues of actin. Brownian dynamics simulations modeled interactions between aldolase, GAPDH, and F-actin from muscle and yeast sources. Mutant actin variants with residues 1-4 replaced by alanine were simulated to assess binding free energy. The simulations estimated association free energy for each protein pair. The team compared binding affinities between wild-type and mutant actin structures. Structural differences in the N-terminus were analyzed for their impact on enzyme binding. The study combined experimental crosslinking with computational modeling to validate structural hypotheses.

The crosslinked complex revealed a direct link between aldolase and actin's N-terminal residues. Simulations showed that mutations in residues 1-4 reduced binding free energy by an average of 2.3 kcal/mol. Muscle aldolase bound yeast actin with the same affinity as the double-mutant muscle actin. This finding suggested that the N-terminus of muscle actin is critical for binding. The free energy wells for yeast and mutant actin were shallower than for native rabbit actin. Simulations confirmed that muscle actin has a higher affinity for aldolase and GAPDH than yeast actin. Acidic residues at the N-terminus of yeast actin correlated with lower binding affinity. These results supported the hypothesis that structural differences in the actin N-terminus influence enzyme binding.

The authors concluded that the N-terminus of muscle actin plays a significant role in binding glycolytic enzymes. The simulations supported experimental findings that muscle actin has a higher affinity for aldolase and GAPDH than yeast actin. The study proposed that structural differences in the N-terminus account for this variation. Mutations in residues 1-4 of muscle actin reduced binding free energy, aligning with the yeast actin profile. The shallower free energy wells for yeast and mutant actin suggested weaker interactions. The acidic residues at the N-terminus of yeast actin were directly linked to lower affinity. These findings reinforced the importance of the actin N-terminus in enzyme binding. The research provided a computational framework for understanding actin-enzyme interactions in muscle cells.