Stability studies of the human Bax protein

Abstract

Bax is a member of the Bcl-2 protein family that participates in mitochondrionmediated apoptosis. In the early stages of the apoptotic pathway, Bax migrates from the cytosol to the outer mitochondrial membrane, where it is inserted and usually oligomerizes to build cytochrome c-compatible pores. Although there are several cellular and structural studies about the stability of Bax, its description at the molecular level remains elusive. Therefore, in this work, computational (in silico) studies were performed on the available structural information of Bax, retrieved from the Universal Protein Resource (Uniprot) and the Protein Data Bank (PDB). This work was focused on the most relevant structural changes observed, investigating their relationship with biological experimental results. These studies include sequence analysis and molecular dynamics (MD) simulations of monomeric human Bax at 300, 400, and 500 K. Sequence analysis was useful for identifying conserved regions in the protein that were later related to structural stability and function. In the MD simulations, Bax gradually loses its -helices when it is submitted to high temperatures, yet it maintains its globular conformation. The resistance of Bax to adopt an extended conformation could be due to several interactions that were found to be responsible for maintaining the structural stability of this protein. Among these interactions, electrostatic interactions, hydrophobic interactions, and hydrogen bonds were found. Remarkably, electrostatic interactions were the most relevant to prevent the elongation of the structure. This atomistic description might have important implications for understanding the functionality and stability of Bax in vitro as well as within the cellular environment. The applications of the knowledge about the activation mechanism of Bax include the development of new drugs and therapies for cell death related diseases such as cancer, and the design of new biosensors employing bilipidic membranes based on the modulation of their permeability.