p97/VCP is a member of the AAA ATPase family and has roles in both membrane fusion and ubiquitin dependent protein degradation. Here, we present a 3.6 Angstrom crystal structure of murine p97 in which D2 domain has been modelled as poly-alanine and the remaining similar to100 residues are absent. The resulting structure illustrates a head-to-tail packing arrangement of the two p97 AAA domains in a natural hexameric state with D1 ADP bound and D2 nucleotide free. The head-to-tail packing arrangement observed in this structure is in contrast to our previously predicted tail-to-tail packing model. The linker between the D1 and D2 domains is partially disordered, suggesting a flexible nature. Normal mode analysis of the crystal structure suggests anti-correlated motions and distinct conformational states of the two AAA domains. (C) 2003 Published by Elsevier Inc.