Energy cost of protein gradient formation in cells

Cells make protein gradients for various purposes, such as establishing position information in development or defining cell polarity in the process of cell division. Two classes of mechanisms for maintaining protein gradients in cells have been reported in the literature: i. those that combine protein diffusion and degradation, and ii. mechanisms that involve active transport of proteins by molecular motors. An example of the first mechanism is the Bicoid protein gradient in the Drosophila embryo, which provides positional information to the nuclei during development. A Smy1 gradient along actin cables in budding yeast cells regulates cable length and is formed by active transport of the proteins by myosin motors to the bud neck [1]. Establishing and maintaining these protein gradients require cells to expend energy. In this talk I examine different mechanisms of gradient formation in cells and estimate the energy costs associated with them. I also consider the scaling of the energy expenditure with cell size for the two different models of gradient formation, and discuss when one mechanism is energetically less costly than the other.
References:
[1] J. A. Eskin, A. Rankova, A. B. Johnston, S. L. Alioto, and B. L. Goode, Mol Biol Cell. (2016) 27:828-37.