Forum 03/30/2006

“Structural Correlates of Proteasome Activation and Function”

Ed Gogol – School of Biological Sciences, University of Missouri, Kansas City

Proteasomes are the compartmentalized proteases responsible for most eukaryotic cytoplasmic proteolysis, both in housekeeping and in specifically-targeted manners.  They are built up of a proteolytic core particle (CP) comprised of four rings of seven subunits, and several different regulatory complexes (RC) that in large part determine the cellular activities and targets of proteolysis.   Because of the non-specific nature of the catalytic sites of the proteasome, its activity must be controlled in the cellular environment to prevent digestion of unintended substrates.  The sequestering of the active sites in the interior of the CP prevents the hydrolysis of most folded proteins, though not of smaller polypeptides.  The RCs serve to select substrates and cause their transit into the interior of the CP, for those CPs in complex with them.  However, the CPs themselves appear to be variable in their activity toward suitable substrates (peptides and loosely-folded proteins).  Part of our study has been an attempt to directly visualize changes in the CP among different states: Latent, active, and inhibited (by a specific polypeptide inhibitor).  Earlier visualization by AFM suggested large-scale changes between the first two states.  CryoEM reconstructions contradict these observations, but do indicate more subtle differences whose basis is not yet clear.  We have also begun to examine CP-RC complexes, in preparations rapidly isolated from yeast cell extracts, in hopes of identifying and describing the nature of the interaction between the RC, natural substrates, and the adapter complexes that are suspected to be involved in delivering them.