“I-型二磷酸核酮糖羧化酶/加氧酶”（Rubisco form I）是自然界最丰富的蛋白，在很多植物和藻青菌（蓝细菌）的光合作用中催化大气二氧化碳的吸收。它是生物技术工作者的一个主要目标，因为如果其有限的催化效率能够提高，也许就有可能利用它来培育改良的作物。
利用试管重建和低温电子显微镜对来自名为“聚球藻”（Synecho-coccus）的一种藻青菌加氧酶所做研究显示，GroEL/GroES伴侣蛋白的亚单元折叠与亚单元组合因伴侣蛋白RbcX2而密切关联，后者起一个“分子订书针”的作用。以这种方式来重建加氧酶的方法，也许可用作再造具有潜在更高效率加氧酶的一个有用工具。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 463, 197-202 (14 January 2010) | doi:10.1038/nature08651
Coupled chaperone action in folding and assembly of hexadecameric Rubisco
Cuimin Liu1,4, Anna L. Young2,4, Amanda Starling-Windhof1, Andreas Bracher1, Sandra Saschenbrecker1, Bharathi Vasudeva Rao1, Karnam Vasudeva Rao1, Otto Berninghausen2, Thorsten Mielke3, F. Ulrich Hartl1, Roland Beckmann2 & Manajit Hayer-Hartl1
1 Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
2 Gene Centre and Center for Integrated Protein Science CIPSM, Department of Chemistry and Biochemistry, University of Munich, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
3 UltraStructure Network, USN, Max Planck Institute for Molecular Genetics, Ihnestrasse 63–73, 14195 Berlin and Charité – Unversit?tsmedizin Berlin, Institut für Medizinische Physik und Biophysik, Ziegelstra?e 5–9, 10098 Berlin, Germany
4 These authors contributed equally to this work.
5 Correspondence to: F. Ulrich Hartl1Roland Beckmann2Manajit Hayer-Hartl1 Correspondence and requests for materials should be addressed to M.H-H., R.B. or F.U.H.
Form I Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase), a complex of eight large (RbcL) and eight small (RbcS) subunits, catalyses the fixation of atmospheric CO2 in photosynthesis. The limited catalytic efficiency of Rubisco has sparked extensive efforts to re-engineer the enzyme with the goal of enhancing agricultural productivity. To facilitate such efforts we analysed the formation of cyanobacterial form I Rubisco by in vitro reconstitution and cryo-electron microscopy. We show that RbcL subunit folding by the GroEL/GroES chaperonin is tightly coupled with assembly mediated by the chaperone RbcX2. RbcL monomers remain partially unstable and retain high affinity for GroEL until captured by RbcX2. As revealed by the structure of a RbcL8–(RbcX2)8 assembly intermediate, RbcX2 acts as a molecular staple in stabilizing the RbcL subunits as dimers and facilitates RbcL8 core assembly. Finally, addition of RbcS results in RbcX2 release and holoenzyme formation. Specific assembly chaperones may be required more generally in the formation of complex oligomeric structures when folding is closely coupled to assembly.
