Skip to main content
eScholarship
Open Access Publications from the University of California

UC Berkeley

UC Berkeley Electronic Theses and Dissertations bannerUC Berkeley

Molecular stochaticity in mammalian cell signaling: Lipid membrane organization and CaMKII kinetics

Abstract

Molecular processes viewed at the single molecule level are stochastic and living cells are full of stochastic processes. Cellular processes frequently occur with a discrete number of molecules and understanding the stochastic behavior of them is of fundamental importance. Here, I studied physical chemistry of two important molecular species in cells: the lipid and the protein.

On the subject of lipids, I studied miscibility phase structure of the live cell membrane. Observations of liquid-liquid miscibility phase transition in ternary mixture membranes with hypothetical existence of heterogeneous membrane domains in mammalian cells caused hypothesis of immiscible domains in live cell membranes. Discussion on the subject is often misleading when the discussion is only focused on the qualitative picture of domain existence, but does not consider the physical principles behind it. The question is where in the phase diagram the living cell membrane is poised. To address this question directly I observed physical parameters of the live cell membrane as a function of temperature and I conclude that the live cell membrane is poised reasonably far from the transition temperature. I also discuss the lack of direct evidence for miscibility phase structures playing an important role in actual signaling and the implication of criticality in membrane reactions.

On the subject of protein, I studied kinetics of CaMKII, a major protein involved in hippocampal synaptic plasticity. CaMKII holoenzyme has a complex structure comprising of twelve subunits and as a molecular component in a neuronal signaling network, this complex structure allows the enzyme to carry out complicated functions. Using a recently solved x-ray crystallographic structure of the CaMKII holoenzyme, I have modeled the relationship between docked-extended states equilibrium and the calcium frequency response of CaMKII. Stochastic kinetics simulations show that CaMKII frequency response can be fine-tuned by adjusting the equilibrium constant. I also show for the first time, activation dependent subunit exchange of CaMKII dodecamer using single molecule TIRF microscopy. This strongly supports the hypothesis that the CaMKII dodecamer, with its continuous turnover of subunits, can serve as a form of molecular memory.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View