Molecular dynamic studies on the impact of mutations on the structure, stability, and N-terminal orientation of annexin A1: implications for membrane aggregation.

Multiple MD simulations were performed for the full-length wild-type A1, the full length A1 mutations S27E and S27A, as well as the N-terminal peptide (AMVSEFLKQAWFIDNEEQEYIKTVKGS²⁷KGGPGSAVSPYPTFN) of wild-type A1 and mutations S27E and S27A. The MD simulation trajectories of about 350 ns were generated and analyzed to examine the changes of core domain calcium binding affinity, core domain and N-terminal domain structures, and N-terminal domain orientation. Our results indicated that S27A and S27E mutations caused little changes on the calcium-binding affinity of the core domain of A1. However, the S27A mutation made the N-terminal domain of A1 less helical, and made the N-terminal domain migrate faster toward the core domain; these impacts on A1 are beneficial to the membrane aggregation process. On the contrary, the S27E mutation made the N-terminal domain of A1 more stable, and hindered the migration to the core domain; these changes on A1 are antagonistic for the membrane aggregation process. Our results using MD simulations provide an atomistic explanation for experimental observations that the S27E mutant showed a higher calcium concentration requirement and lower maximal extent of aggregation, while the wild-type and two mutants S27E and S27A required identical calcium concentrations for liposome binding.