美国Baylor医学院（BCM）的研究者最近发现：当蛋白和多蛋白质复合物处于和它们存在的自然条件类似的环境中时，它们的组装可能会表现出与在常规静态研究条件下的活动或动力学上的不同。这一结果发表于最新一期的《结构》杂志中
Steven Ludtke博士是BCM的生化与分子生物学助理教授，同时也是BCM国立大分子影像中心的副主管，他和BCM以及处于达拉斯的德克萨斯大学西南医学中心的同事们在一项使用冷冻电子显微镜技术的研究中，发现一种称为GroEL蛋白的突变型具有动态行为，这种蛋白能伴随或帮助错误折叠蛋白分子折叠成能正确的形状，以完成其细胞内生理功能，而错误折叠蛋白往往牵涉到许多神经变性和其他疾病。
    冷冻电子显微镜能帮助科学家取得非常详细的单一分子在类天然环境中的二维图象，然后通过电脑和计算生物学的运用，可以将一系列的二维图象重新整合成能表现蛋白动力学的三维结构模型。当Ludtke和他的同事们运用这套方法研究GroEL突变体和它的姐妹蛋白GroES时，他们惊讶地观测到：除了两个预测中结构之外，还有另一个奇怪的结构，Ludtke描述它就像充满了气的气球，而这种膨胀结构之前从未被观测过。
    这种膨胀结构直接关系到蛋白的组装功能。更全面的看法是这是研究任何大分子在溶液中如何表现的有力证据。
Figure 1. Typical Cryo-Images and Representative Reference-free 2D Class Averages
(A and B) Raw images collected on a Gatan 4k × 4k CCD on a JEOL 2010F electron cryomicroscope (scale bar is 200 Å). The white arrows indicate two particles disassociated from GroES. Both images are the farther-from-focus images from a focal pair and are 4 μm under focus. (A) The substrate-free SR398-GroES-Mg-ATP complex. (B) The SR398-αβ-GroES-Mg-ATP complex.
(C and D) Representative reference-free 2D class averages generated from the full set of SR398-GroES-Mg-ATP and SR398-αβ-GroES-Mg-ATP images, respectively (31,163 and 24,162 particles respectively). In each case 300 class averages were generated, a representative subset of which is shown. The number of particles in each class average ranges from 50 to 150. The first row contains views near the symmetric axis. The second row contains various intermediate tilts. The third row shows side views of particles disassociated from GroES. The 4th and 5th rows contain side views of GroES-associated particles. In both sets, the side views exhibit a clear axial protrusion from the base of the structure, as indicated by the white arrows. There is substantial heterogeneity in the substrate-bound case, so additional representative class averages are shown.

原文出处：
Structure November, 2006: 14 (11)  1711－1722
An Expanded Conformation of Single-Ring GroEL-GroES Complex Encapsulates an 86 kDa Substrate
Dong-Hua Chen, Jiu-Li Song, David T. Chuang, Wah Chiu, and Steven J. Ludtke
[Summary] [Full Text] [PDF] [Supplemental Data] 

Articles that cite this article：
Single-Ring GroEL: An Expanded View
Sharon Grayer Wolf
Structure, 2006, 14:11:1599-1600
[Summary] [Full Text] [PDF] 
作者简介：
Steven J. Ludtke
 Asst. Professor of Biochemistry and Molecular Biology and
 Co-director of the National Center for Macromolecular Imaging 
 at Baylor College of Medicine (not affiliated with Baylor University)
 Grad. School: Rice University, PhD in Physics 1996
 Undergrad: Caltech (Lloyd House), graduated 1990
 Check my curriculum vitae for more.
I also have a personal home page

My work involves the 3D reconstruction of molecules and macromolecules using a technique called single particle reconstruction. My most significant contribution to the field is the development of the EMAN software suite, which performs semi-automated processing of electron cryomicrographs to produce accurate 3D reconstructions at subnanometer resolutions. In this technique, a solution containing large molecules and macromolecular assemblies is vitrified (frozen in non-crystalline ice) on an electron microscope grid. It is then imaged at liquid helium or liquid nitrogen temperatures on a transmission electron microscope. Images of individual molecules/assemblies are then collected. These images are very noisy, but represent the solution-like structure of the molecule under study. A large number (1000-100,000) of these particles are then processed using a series of algorithms (implemented in EMAN) to produce accurate volumetric reconstructions of the molecule at resolutions now approaching 0.5 nm (slightly worse than atomic resolution). This technique can also be applied to heterogeneous specimens, such as those existing in multiple functional states.
A growing number of labs around the world are now equipped to collect data using this technique. The NCMI, as an NCRR funded center, participates in both collaborative and service projects using its 4 state of the art electron cryomicroscopes. Visit the NCMI home page if you are interested in performing an experiment using our facilities.
Publications：
CryoEM Related
 Jiang W, Ludtke SJ. (2005) Electron cryomicroscopy of single particles at subnanometer resolution. Curr Opin Struct Biol.
 Ludtke, S.J., Serysheva, I.I., Hamilton, S.L. and Chiu, W. (2005) The pore structure of the closed RyR1 channel. Structure. 8:1203-11.
 Sitharaman, B., Kissell, K.R., Hartman, K.B., Tran, L.A., Baikalov, A., Rusakova, I., Sun, Y., Khant, H.A., Ludtke, S.J., Chiu, W., Laus, S., Toth, E., Helm, L., Merbach, A.E. and Wilson, L.J.. (2005) Superparamagnetic gadonanotubes are high-performance MRI contrast agents. Chem. Commun. 31:3915-7.
 Menetret, J.F., Hegde, R.S., Heinrich, S.U., Chandramouli, P., Ludtke, S.J., Rapoport, T.A., and Akey, C.W. (2005). Architecture of the ribosome-channel complex derived from native membranes. J. Mol. Biol. 348,445-57.
 Serysheva, I.I, Hamilton, S.L., Chiu, W., Ludtke, S.J. (2005). Structure of Ca2+ Release Channel at 14 Å Resolution. J. Mol. Biol., 345, 427-431.
 Zhu, Y., Carragher, B., Glaeser, R.M., Fellmann, D., Bajaj, C., Bern, M., Mouche, F., de Haas, F., Hall, R.J., Kriegman, D.J., Ludtke, S.J., Mallick, S.P., Penczek, P.A., Roseman, A.M., Sigworth, F.J., Volkmann, N., and Potter, C.S. (2004). Automatic particle selection: results of a comparative study. J Struct Biol 145, 3-14.
 Mao, Y., Vyas, N.K., Vyas, M.N., Chen, D.H., Ludtke, S.J., Chiu, W., and Quiocho, F.A. (2004). Structure of the bifunctional and Golgi-associated formiminotransferase cyclodeaminase octamer. Embo J 23, 2963-2971.
 Ludtke, S.J., Chen, D.H., Song, J.L., Chuang, D.T., and Chiu, W. (2004). Seeing GroEL at 6 A resolution by single particle electron cryomicroscopy. Structure (Camb) 12, 1129-1136.
 Chen, C., Ko, Y., Delannoy, M., Ludtke, S.J., Chiu, W., and , P.L. Pedersen (2004). Mitochondrial ATP synthasome: three-dimensional structure by electron microscopy of the ATP synthase in complex formation with carriers for Pi and ADP/ATP. J Biol Chem 279, 31761-31768.
 Brink, J., Ludtke, S.J., Kong, Y., Wakil, S.J., Ma, J., and Chiu, W. (2004). Experimental verification of conformational variation of human fatty acid synthase as predicted by normal mode analysis. Structure (Camb) 12, 185-191.
 Booth, C.R., Jiang, W., Baker, M.L., Zhou, Z.H., Ludtke, S.J., and Chiu, W. (2004). A 9 angstroms single particle reconstruction from CCD captured images on a 200 kV electron cryomicroscope. J Struct Biol 147, 116-127.
 Serysheva, II, Bare, D.J., Ludtke, S.J., Kettlun, C.S., Chiu, W., and Mignery, G.A. (2003). Structure of the type 1 inositol 1,4,5-trisphosphate receptor revealed by electron cryomicroscopy. J Biol Chem 278, 21319-21322.
 Ludtke, S.J., and Chiu, W. (2003). Focal pair merging for contrast enhancement of single particles. J Struct Biol 144, 73-78.
 Ludtke, S.J., Nason, L., Tu, H., Peng, L., and Chiu, W. (2003). Object oriented database and electronic notebook for transmission electron microscopy. Microsc Microanal 9, 556-565.
 Serysheva, II, Ludtke, S.J., Baker, M.R., Chiu, W., and Hamilton, S.L. (2002). Structure of the voltage-gated L-type Ca2+ channel by electron cryomicroscopy. Proc Natl Acad Sci U S A 99, 10370-10375.
 Ludtke, S.J., and Chiu, W. (2002). Image restoration in sets of noisy electron micrographs. In IEEE International Symposium on Biomedical Imaging. pp. WA-SS-2.2, IEEE: Washington, D.C.
 Brink, J., Ludtke, S.J., Yang, C.Y., Gu, Z.W., Wakil, S.J., and Chiu, W. (2002). Quaternary structure of human fatty acid synthase by electron cryomicroscopy. Proc Natl Acad Sci U S A 99, 138-143.
 Baker, M.L., Serysheva, II, Sencer, S., Wu, Y., Ludtke, S.J., Jiang, W., Hamilton, S.L., and Chiu, W. (2002). The skeletal muscle Ca2+ release channel has an oxidoreductase-like domain. Proc Natl Acad Sci U S A 99, 12155-12160.
 Saad, A., Ludtke, S.J., Jakana, J., Rixon, F.J., Tsuruta, H., and Chiu, W. (2001). Fourier amplitude decay of electron cryomicroscopic images of single particles and effects on structure determination. J Struct Biol 133, 32-42.
 Ludtke, S.J., and Chiu, W. (2001). Electron micrographs: computer enhancement and use for molecular 3-dimensional reconstruction. In Encyclopedia of Life Sciences, Volume 6. (London: Nature Publishing Group), pp. 212-217.
 Ludtke, S.J., and Chiu, W. (2001). Editorial: Special Issue on Single Particle Processing. J Struct Biol 133, 89.
 Ludtke, S.J., Jakana, J., Song, J.L., Chuang, D.T., and Chiu, W. (2001). A 11.5 A single particle reconstruction of GroEL using EMAN. J Mol Biol 314, 253-262.
 Jiang, W., Baker, M.L., Ludtke, S.J., and Chiu, W. (2001). Bridging the information gap: computational tools for intermediate resolution structure interpretation. J Mol Biol 308, 1033-1044.
 Ludtke, S.J., Baldwin, P.R., and Chiu, W. (1999). EMAN: semiautomated software for high-resolution single-particle reconstructions. J Struct Biol 128, 82-97.
Membrane Peptides
 Heller, W.T., He, K., Ludtke, S.J., Harroun, T.A., and Huang, H.W. (1997). Effect of changing the size of lipid headgroup on peptide insertion into membranes. Biophys J 73, 239-244.
 Ludtke, S.J., He, K., Heller, W.T., Harroun, T.A., Yang, L., and Huang, H.W. (1996). Membrane pores induced by magainin. Biochemistry 35, 13723-13728.
 He, K., Ludtke, S.J., Worcester, D.L., and Huang, H.W. (1996). Neutron scattering in the plane of membranes: structure of alamethicin pores. Biophys J 70, 2659-2666.
 He, K., Ludtke, S.J., Heller, W.T., and Huang, H.W. (1996). Mechanism of alamethicin insertion into lipid bilayers. Biophys J 71, 2669-2679.
 Wu, Y., He, K., Ludtke, S.J., and Huang, H.W. (1995). X-ray diffraction study of lipid bilayer membranes interacting with amphiphilic helical peptides: diphytanoyl phosphatidylcholine with alamethicin at low concentrations. Biophys J 68, 2361-2369.
 Ludtke, S., He, K., and Huang, H. (1995). Membrane thinning caused by magainin 2. Biochemistry 34, 16764-16769.
 Huang, H.W., He, K., Heller, W.T., and Ludtke, S.J. eds. (1995). Interation of Lipid Bilayer Membranes with Amphiphilic Helical Peptides in Short and Long Chains at Interfaces (Paris, France).
 He, K., Ludtke, S.J., Huang, H.W., and Worcester, D.L. (1995). Antimicrobial peptide pores in membranes detected by neutron in-plane scattering. Biochemistry 34, 15614-15618.
 Ludtke, S.J., He, K., Wu, Y., and Huang, H.W. (1994). Cooperative membrane insertion of magainin correlated with its cytolytic activity. Biochim Biophys Acta 1190, 181-184.
 He, K., Ludtke, S.J., Wu, Y., Huang, H.W., Andersen, O.S., Greathouse, D., and Koeppe, R.E., 2nd (1994). Closed state of gramicidin channel detected by X-ray in-plane scattering. Biophys Chem 49, 83-89.
 He, K., Ludtke, S.J., Wu, Y., and Huang, H.W. (1993). X-ray scatteriing in the plane of membrane. Journal de Physique IV 3, 265-270.
 He, K., Ludtke, S.J., Wu, Y., and Huang, H.W. (1993). X-ray scattering with momentum transfer in the plane of membrane. Application to gramicidin organization. Biophys J 64, 157-162.
Other
 Boehm, F., Bonvin, E., Hatamian, S., Herikson, H., Ludtke, S.J., and van Bladel, K. (1991). A large, low-energy neutrino detector for neutrino oscillations and supernovae watch. Nuclear Instruments and Methods in Physics Research A300, 395-402.

                                                                                       摘自《生物谷》