PLoS Biol:特殊蛋白質如何殺滅癌細胞

2015年2月7日 訊 /生物谷BIOON/ --可食用的平菇往往有著神奇的一面，它們可以通過一種特殊的蛋白「吃掉」蜘蛛和線蟲；然而我們機體的免疫系統也有特殊的一面，通過破壞感染性細胞、癌細胞及細菌來保護機體不受侵害。近日，一篇發表於國際雜誌PLoS Biology上的研究論文中，來自澳洲莫納斯大學的研究人員通過研究揭示了免疫細胞保護機體不為人知的一面。

利用同步加速器和低溫電子顯微檢查技術，研究者對名為側耳溶血素(pleurotolysin)的蛋白質的功能進行了研究，從而為開發新型靶向藥物及工具提供了新思路；通過分子快照技術，研究者就可以將側耳溶血素的活動過程轉化成為視頻影像來展現其特殊的打孔蛋白，這種打孔蛋白可以在靶向細胞上打孔進而有效殺滅細胞，同時也為其它殺傷性細胞提供了一個作用通道。

研究者Michelle Dunstone說道，我曾經並不認為可以觀察到這種特殊蛋白的作用方式，但在新型技術的幫助下我們如今可以清楚地觀察到這種打孔蛋白的作用過程了；通過分子成像，結合生物物理學及計算機相關模擬試驗，研究小組闡明了側耳溶血素蛋白的運動方式，以及其如何伸展及重摺疊從而在靶向細胞上打孔，與此同時研究者也發現了這種蛋白的要害部位，這樣研究者就可以觀察如何阻斷打孔的機制，或者是將側耳溶血素蛋白引入到可以發揮更大用途的位置。

下一步研究人員將選取從平菇中提取的蛋白來將其同自然界中的相同蛋白進行對比，當然研究者尤其感興趣於研究人類機體中的蛋白家族，尤其是穿孔素，其被認為同上述蛋白質的作用方式相同。這些蛋白在醫藥研究領域均具有潛在的應用價值，比如抑制自體免疫疾病患者的免疫反應或阻斷李斯特菌從免疫細胞中逃逸等。

最後研究者Helen Saibil說道，目前我們還有大量的工作需要去做，後期我們將對側耳溶血素的更多功能進行研究，希望其早日可以應用於臨床中幫助治療疾病改善患者的生活質量。（生物谷Bioon.com）

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Conformational Changes during Pore Formation by the Perforin-Related Protein Pleurotolysin

Lukoyanova N, Kondos SC, Farabella I, Law RHP, Reboul CF, et al.

 

Membrane attack complex/perforin-like (MACPF) proteins comprise the largest superfamily of pore-forming proteins, playing crucial roles in immunity and pathogenesis. Soluble monomers assemble into large transmembrane pores via conformational transitions that remain to be structurally and mechanistically characterised. Here we present an 11 Å resolution cryo-electron microscopy (cryo-EM) structure of the two-part, fungal toxin Pleurotolysin (Ply), together with crystal structures of both components (the lipid binding PlyA protein and the pore-forming MACPF component PlyB). These data reveal a 13-fold pore 80 Å in diameter and 100 Å in height, with each subunit comprised of a PlyB molecule atop a membrane bound dimer of PlyA. The resolution of the EM map, together with biophysical and computational experiments, allowed confident assignment of subdomains in a MACPF pore assembly. The major conformational changes in PlyB are a ~70° opening of the bent and distorted central β-sheet of the MACPF domain, accompanied by extrusion and refolding of two α-helical regions into transmembrane β-hairpins (TMH1 and TMH2). We determined the structures of three different disulphide bond-trapped prepore intermediates. Analysis of these data by molecular modelling and flexible fitting allows us to generate a potential trajectory of β-sheet unbending. The results suggest that MACPF conformational change is triggered through disruption of the interface between a conserved helix-turn-helix motif and the top of TMH2. Following their release we propose that the transmembrane regions assemble into β-hairpins via top down zippering of backbone hydrogen bonds to form the membrane-inserted β-barrel. The intermediate structures of the MACPF domain during refolding into the β-barrel pore establish a structural paradigm for the transition from soluble monomer to pore, which may be conserved across the whole superfamily. The TMH2 region is critical for the release of both TMH clusters, suggesting why this region is targeted by endogenous inhibitors of MACPF function.