Macromolecular Organization and Cell Function: A Multi-System Analysis

Abstract

The interior of the cell is a densely crowded and complex arena, full of a vast and diverse array of molecules and macromolecules. A fundamental understanding of cellular physiology will depend not only upon a reductionist analysis of the chemistry, structure, and function of individual components and subsystems, but also on a sagacious exegesis of the dynamic and emergent properties that characterize the higher-level system of living cells. Here, we present work on two aspects of the supramolecular organization of the cell: the controlled assembly of the mitotic spindle during cell division and the regulation of cellular metabolism through the formation of multienzyme complexes.

During division, the cell undergoes a profound morphological and molecular reorganization that includes the creation of the mitotic spindle, a process that must be highly controlled in order to ensure that accurate segregation of hereditary material. Chapter 2 describes results that implicate the kinase, Zeste-white3/Shaggy (Zw3/Sgg), as having a role in regulating spindle morphology.

The congregation of metabolic enzymes into macromolecular complexes is a key feature of cellular physiology. Given the apparent pervasiveness of these assemblies, it seems likely that some of the mechanisms involved in their organization and regulation might be conserved across a range of biosynthetic pathways in diverse organisms. The Winkel laboratory makes use of the flavonoid biosynthetic pathway in Arabidopsis as an experimental model for studying the architecture, dynamics, and functional roles of metabolic complexes. Over the past several years, we have accumulated substantive and compelling evidence indicating that a number of these enzymes directly interact, perhaps as part of a dynamic globular complex involving multiple points of contact between proteins. Chapter 3 describes the functional analysis of a predicted flavonol synthase gene family in Arabidopsis. The first evidence for the interaction of flavonoid enzymes in living cells, using fluorescent lifetime imaging microscopy fluorescent resonance energy transfer analysis (FLIM-FRET), is presented in Chapter 4.