Effect of GroEL on Thermal Aggregation of Glycogen Phosphorylase b from Rabbit Skeletal Muscle a Tatyana B. Eronina,* Natalia A. Chebotareva, Svetlana G. Bazhina, Sergey Y. Kleymenov, Irina N. Naletova, Vladimir I. Muronetz, Boris I. Kurganov Introduction Chaperones are molecules that assist proteins during folding, protect them from aggregation and facilitate correct protein folding during heat stress. [1] The GroEL molecular chaperone from Escherichia coli is a member of the highly conserved heat shock protein 60 (HSP60) family of such proteins. [2] The GroEL molecule is a porous cylinder consisting of 14 identical subunits of 57 kDa, each made of two 7-fold rings stacked back-to-back. [3] The GroL chaper- onin system consists of two homo-oligomeric proteins, GroEL and GroES, and assists folding of various proteins through multiple rounds of binding of protein targets in the inner cavity of the GroEL ring and release of protein substrate. [4] It has been demonstrated that GroEL suppresses the aggregation of proteins. [5,6] It has been suggested that hydrophobic interactions represent the main factor stabi- lizing the GroEL complex with non-native proteins. [7] However, electrostatic interactions also play an important role in the complexing of GroEL with non-native proteins. [8] Ybarra and Horowitz [9] and Surin et al. [10] have shown that the conditions commonly used for the preparation of GroEL (the simultaneous presence of Mg-adenosine triphosphate (Mg-ATP) or Mg-adenosine diphosphate (Mg- ADP) and a solid-phase anion-exchange medium) favor the Full Paper T. B. Eronina, N. A. Chebotareva, S. G. Bazhina, S. Y. Kleymenov, B. I. Kurganov Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky 33, Moscow, 119071, Russia Fax: (þ7-495) 954 2732; E-mail: eronina@inbi.ras.ru S. Y. Kleymenov Koltsov’s Institute of Developmental Biology, Russian Academy of Sciences, Vavilova 26, Moscow, 119991, Russia I. N. Naletova, V. I. Muronetz Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory, Moscow, 119992, Russia S. G. Bazhina Department of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia a : Supporting information for this article is available at the bottom of the article’s abstract page, which can be accessed from the journal’s homepage at http://www.mbs-journal.de, or from the author. The suppression of the thermal aggregation of glycogen phosphorylase b (Phb) from rabbit skeletal muscle by the chaperonin GroEL is studied using dynamic light scattering. It is shown that the decrease in the rate of Phb aggregation under the action of GroEL is due to the transition of the aggregation process from the kinetic regime, wherein the rate of aggregation is limited by diffusion of the interacting particles, to a regime where the sticking probability for the colliding particles becomes lower than one (reaction-limited clus- ter-cluster aggregation). The analytical-ultracentrifugation data show that elevated temperatures induce dissociation of the dimeric Phb. The formation of a complex between the denatured monomeric form of Phb and the dissociated forms of GroEL is detected during heating at 46 8C. 768 Macromol. Biosci. 2010, 10, 768–774 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mabi.200900396