Title:

Effects of Mutation on Structure and Binding of the Intrinsically Disordered Protein PopZ

Cellular organization has been key factor in creating and maintaining the complex biochemical functions that underlie cellular function. Organization is particularly important in cellular division as the uneven division of important proteins can lead to the death of one or more of the resulting daughter cells. Despite their relative simplicity bacteria also have a complex subcellular anatomy for cellular organization. For example, the bacteria Caulobacter cresentus processes a177-amino acid protein known Polar Organizing Protein Z (PopZ) that self assembles into multiprotein superstructures at the cell poles of the bacterium. These superstructures then bind to at least 8 different proteins at the cell poles that are linked to cell cycle regulation and chromosome segregation. Currently the structure of a C-terminal truncated form of PopZ has been determined using Nuclear Magnetic Resonance (NMR) Spectroscopy to be mostly intrinsically disordered with a small alpha-helix located near the N-terminus of the protein.NMR titration experiments with one of PopZ’s known protein binding partners has also revealed that this alpha-helix is the region of the protein that interacts with the protein binding partner. To further characterize this interaction, an amino acid substituted isoform of the PopZ protein, PopZ I17A, was recombinantly expressed and subjected to the same titration experiment, to determine if isoleucine 17 was critical in the electrostatic binding of PopZ to the protein binding partner. This experiment displayed that the I17A amino acid substitution resulted in a complete loss of function of the PopZ isoform, indicating that isoleucine 17 is critical in the binding of PopZ to its binding partners.

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