Lengyel Jeffrey S, Stott Katherine M, Wu Xiongwu, Brooks Bernard R, Balbo Andrea, Schuck Peter, Perham Richard N, Subramaniam Sriram, Milne Jacqueline L S
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Structure. 2008 Jan;16(1):93-103. doi: 10.1016/j.str.2007.10.017.
Icosahedral pyruvate dehydrogenase (PDH) enzyme complexes are molecular machines consisting of a central E2 core decorated by a shell of peripheral enzymes (E1 and E3) found localized at a distance of approximately 75-90 A from the core. Using a combination of biochemical, biophysical, and cryo-electron microscopic techniques, we show here that the gap between the E2 core and the shell of peripheral enzymes is maintained by the flexible but extended conformation adopted by 60 linker polypeptides that radiate outwards from the inner E2 core, irrespective of the E1 or E3 occupancy. The constancy of the gap is thus not due to protein-protein interactions in the outer protein shell. The extended nature of the E2 inner-linker regions thereby creates the restricted annular space in which the lipoyl domains of E2 that carry catalytic intermediates shuttle between E1, E2, and E3 active sites, while their conformational flexibility facilitates productive encounters.
二十面体丙酮酸脱氢酶（PDH）酶复合物是一种分子机器，由一个中央E2核心和一层外围酶（E1和E3）组成，外围酶位于距离核心约75 - 90埃的位置。通过结合生化、生物物理和冷冻电子显微镜技术，我们在此表明，E2核心与外围酶壳之间的间隙由60条连接多肽从内部E2核心向外辐射所采用的灵活但伸展的构象维持，而与E1或E3的占据情况无关。因此，间隙的恒定并非由于外部蛋白质壳中的蛋白质 - 蛋白质相互作用。E2内部连接区域的伸展性质从而创造了一个受限的环形空间，在其中携带催化中间体的E2的硫辛酰结构域在E1、E2和E3活性位点之间穿梭，而它们的构象灵活性促进了有效的相互作用。
