The DEAD-box adenosine triphosphatase (ATPase) Prp5p facilitates U2 small
nuclear ribonucleoprotein particle (snRNP) binding to the intron branch site
region during spliceosome assembly. We present crystal structures of
S. cerevisiae Prp5p alone and in complex with ADP at 2.12 Å and 1.95 Å
resolution. The three-dimensional packing of Prp5p subdomains differs strikingly
from that so far observed in other DEAD-box proteins: two RecA-like subdomains
adopt an "open state" conformation stabilized by extensive
interactions involving sequences that flank the two subdomains. This
conformation is distinct from that required for ATP hydrolysis. Consistent with
this, Prp5p mutations that destabilize interdomain interactions exhibited
increased ATPase activity in vitro and inhibited splicing of suboptimal branch
site substrates in vivo, whereas restoration of interdomain interactions
reversed these effects. We conclude that the Prp5p open state conformation is
biologically relevant and that disruption of the interdomain interaction
facilitates a large-scale conformational change of Prp5p during U2 snRNP-branch
site recognition.