Structure and function of metabolic enzyme assemblies

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PROJECT SUMMARY Intermediate metabolism must be finely tuned, carefully balanced, and robustly adaptable to changes in envi- ronmental conditions. While the individual enzymes that drive most metabolic processes are well understood, only have we appreciated the widespread role of metabolic enzyme assemblies in metabolic organization and control. In particular, two types of structures, metabolic filaments that assemble from single enzyme types, and metabolons that co-assemble multiple enzymes in single pathways, provide important mechanisms for regulating enzyme activity and metabolic flux. Both filaments and metabolons assemble dynamically in cells, and alter the functions of the constituent enzymes to adapt to metabolic demand. This proposal builds on recent successes from our group describing the molecular mechanisms and functional consequences of enzyme assembly in mul- tiple systems, including nucleotide biosynthesis, energy metabolism, and amino acid regulation. Recent work, including our own published and preliminary data, shows that enzyme assembly is a general mechanism of control, and that assembly itself is controlled by cells in multiple ways, including by the levels of specific metab- olites, by posttranslational modification, by expression of splice variants that alter polymerization characteristics, and by interaction with regulatory proteins. We use in vitro reconstitution and cryo-electron microscopy to deter- mine the structural basis for assembly and regulation, coupled with biochemical, biophysical, and cell biological techniques in an integrative approach to understanding the functions of metabolic assemblies. This work will provide insight into the specific roles assembly plays in modulating the function of multiple enzymes, and illumi- nate general principles of metabolic control.