Formation of insoluble intracellular aggregates due to protein misfolding is a common pathogenetic basis for many degenerative and human neurodegenerative dis- eases including Alzheimer’s, Parkinson’s, Huntington’s, and other diseases [1, 2]. Heat shock proteins (HSPs) playing the role of molecular chaperones [3] and found in all organisms [4], can prevent protein aggregation. Human and animal lens protein, crystallin, is also an HSP. Like other HSPs, it does not exhibit specificity with respect to protein substrates, and αB-crystallin has been found in almost all tissues, including skeletal muscle [5]. In vitro α-crystallin suppressed aggregation of a number of proteins [6-8]. It is suggested that α-crystallin suppres- sion of aggregation of denatured proteins involves its binding to hydrophobic sites of a nonnative protein; increase in temperature increased this ability [9, 10]. The three-dimensional structure of α-crystallin still remains unknown due to its polydispersity and also due to varia- tions of oligomeric state and molecular mass, which may vary depending on temperature and isolation conditions of this protein [11]. In this study, we have investigated the effect of α- crystallin on thermal aggregation of glycogen phosphory- lase b (Phb). Glycogen phosphorylase (1,4-α-D-glu- can:orthophosphate-α-D-glycosyl transferase; EC 2.4.1.1) is the key enzyme of glycogen metabolism in skeletal muscles. Phb catalyzes the first stage of glycogen degradation. In a resting muscle, the enzyme exists in the ISSN 0006-2979, Biochemistry (Moscow), 2007, Vol. 72, No. 5, pp. 518-528. © Pleiades Publishing, Ltd., 2007. Original Russian Text © A. V. Meremyanin, T. B. Eronina, N. A. Chebotareva, S. Yu. Kleimenov, I. K. Yudin, K. O. Muranov, M. A. Ostrovsky, B. I. Kurganov, 2007, published in Biokhimiya, 2007, Vol. 72, No. 5, pp. 642-654. 518 Abbreviations: DSC) differentiation scanning calorimetry; Phb) glycogen phosphorylase b; HSP) heat shock protein. * To whom correspondence should be addressed. Effect of α-Crystallin on Thermal Aggregation of Glycogen Phosphorylase b from Rabbit Skeletal Muscle A. V. Meremyanin 1 *, T. B. Eronina 1 , N. A. Chebotareva 1 , S. Yu. Kleimenov 1 , I. K. Yudin 2 , K. O. Muranov 3 , M. A. Ostrovsky 3 , and B. I. Kurganov 1 1 Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, 119071 Moscow, Russia; fax: (495) 954-2732; E-mail: mer-av@inbi.ras.ru 2 Oil and Gas Research Institute, Russian Academy of Sciences, ul. Gubkina 3, 119991 Moscow, Russia 3 Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, 117997 Moscow, Russia Received December 27, 2006 Abstract—Thermal aggregation of rabbit skeletal muscle glycogen phosphorylase b (Phb) has been investigated using dynam- ic light scattering under conditions of a constant rate of temperature increase (1 K/min). The linear behavior of the depend- ence of the hydrodynamic radius on temperature for Phb aggregation is consistent with the idea that thermal aggregation of proteins proceeds in the kinetic regime wherein the rate of aggregation is limited by diffusion of the interacting particles (the regime of “diffusion-limited cluster–cluster aggregation”). In the presence of α-crystallin, a protein exhibiting chaperone- like activity, the dependence of the hydrodynamic radius on temperature follows the exponential law; this suggests that the aggregation process proceeds in the kinetic regime where the sticking probability for colliding particles becomes lower than unity (the regime of “reaction-limited cluster–cluster aggregation”). Based on analysis of the ratio between the light scat- tering intensity and the hydrodynamic radius of Phb aggregates, it has been concluded that the addition of α-crystallin results in formation of smaller size starting aggregates. The data on differential scanning calorimetry indicate that α-crys- tallin interacts with the intermediates of the unfolding process of the Phb molecule. The proposed scheme of thermal denat- uration and aggregation of Phb includes the stage of reversible dissociation of dimers of Phb into monomers, the stage of the formation of the starting aggregates from the denatured monomers of Phb, and the stage of the sticking of the starting aggre- gates and higher order aggregates. Dissociation of Phb dimer into monomers at elevated temperatures has been confirmed by analytical ultracentrifugation. DOI: 10.1134/S0006297907050082 Key words: glycogen phosphorylase b, denaturation, aggregation, α-crystallin, dynamic light scattering, analytical ultracen- trifugation