PDF(Pubmed)
Abstract：
The phosphoinositide-3 kinase (PI3K), a heterodimeric enzyme, plays a pivotal role in cellular metabolism and survival. Its deregulation is associated with major human diseases, particularly cancer. The p85 regulatory subunit of PI3K binds to the catalytic p110 subunit via its C-terminal domains, stabilising it in an inhibited state. Certain Src homology 3 (SH3) domains can activate p110 by binding to the proline-rich (PR) 1 motif located at the N-terminus of p85. However, the mechanism by which this N-terminal interaction activates the C-terminally bound p110 remains elusive. Moreover, the intrinsically poor ligand selectivity of SH3 domains raises the question of how they can control PI3K. Combining structural, biophysical, and functional methods, we demonstrate that the answers to both these unknown issues are linked: PI3K-activating SH3 domains engage in additional \"tertiary\" interactions with the C-terminal domains of p85, thereby relieving their inhibition of p110. SH3 domains lacking these tertiary interactions may still bind to p85 but cannot activate PI3K. Thus, p85 uses a functional selection mechanism that precludes nonspecific activation rather than nonspecific binding. This separation of binding and activation may provide a general mechanism for how biological activities can be controlled by promiscuous protein-protein interaction domains.
摘要：
磷酸肌醇-3激酶（PI3K），一种异源二聚体酶，在细胞代谢和生存中起着关键作用。它的放松管制与重大人类疾病有关，尤其是癌症。PI3K的p85调节亚基通过其C端结构域与催化p110亚基结合，将其稳定在抑制状态。某些Src同源3(SH3)结构域可以通过与位于p85的N末端的富含脯氨酸(PR)1基序结合来激活p110。然而,这种N端相互作用激活C端结合的p110的机制仍然难以捉摸。此外，SH3结构域固有的低配体选择性提出了它们如何控制PI3K的问题。结合结构，生物物理，和功能方法，我们证明了这两个未知问题的答案是相关的:激活PI3K的SH3结构域与p85的C端结构域参与额外的“三级”相互作用,从而减轻其对p110的抑制作用.缺乏这些三级相互作用的SH3结构域仍可与p85结合,但不能激活PI3K。因此，p85使用功能选择机制，排除非特异性激活而不是非特异性结合。这种结合和激活的分离可以提供一种关于如何通过混杂的蛋白质-蛋白质相互作用结构域来控制生物活性的一般机制。
