Abstract
Caspase-2 is an intracellular protease responsible for the proteol-ysis of cellular substrates directly involved in mediating apoptoticsignaling cascades. Caspase-2 activation is inhibited by phospho-rylation followed by binding to the scaffolding protein 14-3-3,which recognizes two phosphoserines located in the linkerbetween the CARD domain and the large catalytic (p19) domainof the caspase-2 zymogen.
This region with both 14-3-3 bindingmotifs also contains the nuclear localization sequence of caspase-2. Using biochemical and biophysical approaches, we performeda structural analysis of the 14-3-3zeta:caspase-2 complex to eluci-date the structural details of this interaction and the role of 14-3-3 in the regulation of caspase-2 activation.
The structure modelproposed in this study suggests that phosphorylated caspase-2and 14-3-3zeta form a compact and rigid complex in which thelarge (p19) and small (p12) catalytic domains of caspase-2 arepositioned within the central channel of the 14-3-3 dimer and arestabilized through interactions with the C-terminal helices of both14-3-3zeta protomers. In this conformation, the surface of thep12 domain, which is involved in caspase-2 activation by dimer-ization, is sterically occluded by the 14-3-3 dimer, thereby likelypreventing caspase-2 activation.
In addition, 14-3-3 protein bind-ing to caspase-2 masks its nuclear localization sequence suggest-ing that 14-3-3 binding may regulate the subcellular localizationof caspase-2.