Determining the Structural Basis of Cofactor and Substrate Interactions with Cdc48

Abstract

Cdc48 (also known as p97 or VCP) is an essential and abundant AAA+ ATPase. It acts to separate proteins from a variety of contexts, including organelle membranes, ribosomes, protein complexes, and chromatin 1. This "segregase" activity is best described for unfolding proteins that are presented to the proteasome for degradation. Inhibition of human Cdc48 is an emerging therapeutic strategy for cancer treatment 1 and mutations in the human homolog of Cdc48 are linked to diseases such as multisystem proteinopathy 2. Cdc48 has a general structure of two ATPase domains capped by an N-terminal domain. Six Cdc48 subunits bind together in order to form a hexamer that has a central pore with pore loops from each subunit reaching into the pore. The N-terminal domain that sits atop Cdc48 is responsible for the binding of most adaptor proteins of Cdc48 3. Until recently, all published structures show Cdc48 in a six-fold symmetric conformation with no substrate bound. This is true regardless of the nucleotide state of these structures 4-5 。 However, these symmetrical structures most likely do not represent the active state of Cdc48.