Mutations in the Human AAA+ Chaperone p97 and Related Diseases

Abstract

A number of neurodegenerative diseases have been linked to mutations in the human protein p97, an abundant cytosolic AAA⁺ (ATPase associated with various cellular activities) ATPase, that functions in a large number of cellular pathways. With the assistance of a variety of cofactors and adaptor proteins, p97 couples the energy of ATP hydrolysis to conformational changes that are necessary for its function. Disease-linked mutations, which are found at the interface between two main domains of p97, have been shown to alter the function of the protein, although the pathogenic mutations do not appear to alter the structure of individual subunit of p97 or the formation of the hexameric biological unit. While exactly how pathogenic mutations alter the cellular function of p97 remains unknown, functional, biochemical and structural differences between wild-type and pathogenic mutants of p97 are being identified. Here, we summarize recent progress in the study of p97 pathogenic mutants.

Keywords: VCP/p97; conformational changes; multisystem diseases; mutations; structure and function.

Figure 1

Structure of the AAA ATPase p97. (A) Schematic domain organization of a p97 subunit showing the three structural domains: N-terminal N domain and two ATPase domains D1 and D2, and the positions of pathogenic mutations. (B) Ribbon representation of the top and side views of the hexameric structure of ^FLp97 (PDB:3CF2, Davies et al., 2008). The N domain is in purple, D1 domain in blue and D2 domain in gold. (C) The top view of ^ND1p97 structure showing the location of pathogenic mutations. Selected pathogenic mutations (residue I27, R93, I126, P137, R155, R191, L198, I206, A232, T262, N387, N401, A439) are represented as yellow spheres on the ribbon diagram of ^ND1p97 with ADP bound (PDB: 1E32, Zhang et al., 2000).

Figure 2

The Up- and Down-conformation of p97 N domain. Ribbon presentation of the structure of the hexameric ^ND1p97. The D1 domains are colored in blue and the N domains are in purple.

Figure 3

Model proposed for the relationship between control of N domain conformation and ATPase activity in p97. Cartoon representation of a hexameric p97 shows the D1 domains in blue, D2 domains in orange, and the N domains in pink circle. N domains that are labeled with the letter “D” are in the Down-conformation and their corresponding D1 domains are occupied by ADP. N domains that are labeled with the letter “T” are in the Up-conformation and their corresponding D1 domains are occupied with ATP. Only those subunits that have their D1 domains occupied by ATP are capable of hydrolyzing ATP in their D2 domains. The conformation of the N domains is not determined when their corresponding D1 domains are empty (No label in the N domain). Proposed nucleotide binding and hydrolysis cycle for (A) the wild-type p97 and for (B) mutant p97. Mutations are represented by the green dots at the interface between N and D1 domains. Empty state indicates a state in the absence of added ATP or ADP. The ATP state is the presence of added ATP. The ADP-locked state refers to a subset of subunits where ADP in the D1 domain is very tightly bound, whereas the ADP-open state refers to a subset of subunits where ADP molecules in the D1 domains are able to exchange nucleotides with those in solution. The ADP-locked and ADP-open states are in equilibrium in solution.

Figure 4

Structures of p97 in complex with interacting proteins. The N domain of p97 is shown as a surface representation with the two subdomains, double ψ-barrel and β-barrel, in gray and violet, respectively. Individual domains or peptides from different p97-interacting proteins are shown as a cyan cartoon. All the structures were superposed with the N domain of p97 and presented in the same orientation. (A) PDB:1S3S (Dreveny et al., 2004). (B) PDB:4KDI (Kim et al., 2014). (C) PDB:3TIW (Hänzelmann and Schindelin, 2011). (D) PDB:5C1B (Hänzelmann and Schindelin, 2016a).