大腸桿菌的致病菌種將很多蛋白轉位進宿主細胞中,以促進其毒性。這些蛋白中的其中一個(來自大腸桿菌O157:H7的EspG)的結構,已在與兩個宿主酶形成的一個複合物中被確定,其機制也已被弄清。這些結構揭示了EspG是怎樣通過在膜細胞器上的囊泡萌芽反應期間有針對性地識別宿主ARF6酶的與GTP結合的活性狀態來破壞內膜運輸通道的。EspG是直接激發PAK激酶的,其方式是束縛該激酶激發級聯中一個未摺疊的過渡態。(生物谷Bioon.com)
生物谷推薦原文出處:
Nature doi:10.1038/nature09593
The assembly of a GTPase–kinase signalling complex by a bacterial catalytic scaffold
Andrey S. Selyunin,Sarah E. Sutton,Bethany A. Weigele,L. Evan Reddick,Robert C. Orchard,Stefan M. Bresson,Diana R. Tomchick& Neal M. Alto
The fidelity and specificity of information flow within a cell is controlled by scaffolding proteins that assemble and link enzymes into signalling circuits1, 2. These circuits can be inhibited by bacterial effector proteins that post-translationally modify individual pathway components3, 4, 5, 6. However, there is emerging evidence that pathogens directly organize higher-order signalling networks through enzyme scaffolding7, 8, and the identity of the effectors and their mechanisms of action are poorly understood. Here we identify the enterohaemorrhagic Escherichia coli O157:H7 type III effector EspG as a regulator of endomembrane trafficking using a functional screen, and report ADP-ribosylation factor (ARF) GTPases and p21-activated kinases (PAKs) as its relevant host substrates. The 2.5?? crystal structure of EspG in complex with ARF6 shows how EspG blocks GTPase-activating-protein-assisted GTP hydrolysis, revealing a potent mechanism of GTPase signalling inhibition at organelle membranes. In addition, the 2.8?? crystal structure of EspG in complex with the autoinhibitory Iα3-helix of PAK2 defines a previously unknown catalytic site in EspG and provides an allosteric mechanism of kinase activation by a bacterial effector. Unexpectedly, ARF and PAKs are organized on adjacent surfaces of EspG, indicating its role as a 『catalytic scaffold』 that effectively reprograms cellular events through the functional assembly of GTPase-kinase signalling complex.