Yan Nieng, Huh Jun R, Schirf Virgil, Demeler Borries, Hay Bruce A, Shi Yigong
Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, New Jersey 08544, USA.
J Biol Chem. 2006 Mar 31;281(13):8667-74. doi: 10.1074/jbc.M513232200. Epub 2006 Jan 30.
Activation of an initiator caspase is essential to the execution of apoptosis. The molecular mechanisms by which initiator caspases are activated remain poorly understood. Here we demonstrate that the autocatalytic cleavage of Dronc, an important initiator caspase in Drosophila, results in a drastic enhancement of its catalytic activity in vitro. The autocleaved Dronc forms a homodimer, whereas the uncleaved Dronc zymogen exists exclusively as a monomer. Thus the autocatalytic cleavage in Dronc induces its stable dimerization, which presumably allows the two adjacent monomers to mutually stabilize their active sites, leading to activation. Crystal structure of a prodomain-deleted Dronc zymogen, determined at 2.5 A resolution, reveals an unproductive conformation at the active site, which is consistent with the observation that the zymogen remains catalytically inactive. This study revealed insights into mechanism of Dronc activation, and in conjunction with other observations, suggests diverse mechanisms for the activation of initiator caspases.
起始半胱天冬酶的激活对于细胞凋亡的执行至关重要。起始半胱天冬酶被激活的分子机制仍知之甚少。在此我们证明，果蝇中一种重要的起始半胱天冬酶Dronc的自催化切割在体外会导致其催化活性大幅增强。自切割的Dronc形成同源二聚体，而未切割的Dronc酶原仅以单体形式存在。因此，Dronc中的自催化切割诱导其稳定二聚化，这可能使两个相邻单体相互稳定其活性位点，从而导致激活。以2.5埃分辨率测定的缺失前结构域的Dronc酶原的晶体结构显示，活性位点存在无活性构象，这与酶原仍无催化活性的观察结果一致。这项研究揭示了Dronc激活机制的见解，并与其他观察结果一起，提示了起始半胱天冬酶激活的多种机制。
