Site-directed spin labeling was used to investigate quaternary interactions along a conserved sequence in the ␣-crystallin domain of ␣A-crystallin, heat-shock protein 27 (HSP 27), and Mycobacterium tuberculosis heatshock protein (HSP 16.3). In previous work, it was demonstrated that this sequence in ␣A-crystallin and HSP 27 forms a ␤-strand involved in subunit contacts. In this study, the symmetry and geometry of the resulting interface were investigated. For this purpose, the pattern of spin-spin interactions was analyzed, and the number of interacting spins was determined in ␣A-crystallin and HSP 27. The results reveal a 2-fold symmetric interface consisting of two ␤-strands interacting near their N termini in an antiparallel fashion. Remarkably, subunit interactions along this interface persist when the ␣-crystallin domains are expressed in isolation. Because this domain in ␣A-crystallin forms dimers and tetramers, it is inferred that interactions along this interface mediate the formation of a basic dimeric unit. In contrast, in HSP 16.3, spin-spin interactions are observed at only one site near the C terminus of the sequence. Furthermore, cysteine substitutions at residues flanking the N terminus resulted in the dissociation of the oligomeric structure. Analysis of the spin-spin interactions and size exclusion chromatography indicates a 3-fold symmetric interface. Taken together, our results demonstrate that subunit interactions in the ␣-crystallin domain of mammalian small heat-shock proteins assemble a basic building block of the oligomeric structure. Sequence divergence in this domain results in variations in the size and symmetry of the quaternary structure between distant members of the small heat-shock protein family.In response to exposure to high temperature and other forms of stress, cells and organisms express multiple families of heatshock proteins (HSP) 1 (1). The function of these proteins is to confer thermotolerance via a variety of mechanisms including suppression of aggregation and refolding of denatured proteins.The small heat-shock protein (sHSP) family consists of proteins with molecular mass Ͻ40 kDa and possessing a stretch of 80 -100 amino acids that shows sequence similarities to lens ␣-crystallins, the ␣-crystallin domain (2). The extent of sequence similarity in this domain is variable, ranging from 20% between distant members of the family (e.g. bacterial and mammalian sHSP) to over 60% between mammalian sHSP (2-4). Flanking the ␣-crystallin domain are an N-terminal region, characterized by extensive sequence and length variability, and a polar nonconserved C-terminal tail (2). The patterns of abundance and expression of sHSP are also speciesspecific. For instance, heat-stressed plant cells express over 25 sHSP (3), while mammalian cells express two: HSP 25/27 and ␣B-crystallin (5, 6). Although their cellular function is not well understood, in vitro sHSP bind unfolding proteins in a stable complex (7,8). This chaperone-like function does not require ATP, and sHSP do not have an in...

The aim of this work is to assemble the computer models of phase diagrams (PD) for the typical ternary systems and to examine the processes of crystallization on its base. Spatial schemes of mono-and invariant equilibria have been used for it. Analysis of concentration fields, obtained by the projection of the surfaces on the Gibbs triangle, allows establish the boundaries of phase regions (located above the considered fields), the sequence of phase transformations and microstructural elements for the solidification of the initial melt at equilibrium condition. Concentration fields have been analyzed by means of mass balances for their centers of masses. Based on this technology, the research identifies concentration fields with coinciding sets of phase reactions and microconstituents, and the fields with individual characteristics.

New algorithm has been offered to divide a concentration complex of reciprocal system for the subsystems. It is based on the relations between the number of complex polyhedron vertexes and resulting number of simplexes. Method is demonstrated on the quaternary systems. It is easy realized in the software, and is very effective in the cases with inner points (compounds) and with the competition of inner diagonals.

Three-dimensional (3D) computer model of the Al-Sn-Zn isobaric phase diagram is presented. It is shown that the T-x-y diagram consists of 64 surfaces and 25 phase regions. Features of Al-Zn binary system phase diagram related to decomposition of aluminum solid solution and its influence on geometric structure of liquidus and solidus surfaces in the ternary system, formed by this binary system and tin, are considered. Critical analysis of the published data was carried out and errors in visualization of those fragments of the Al-Zn T-x diagram, in which phase regions are formed with the participation of new aluminum solid solutions, appeared after the decomposition of the initial solid solution, are discussed. To design this 3D model, literary data were used, and the assessment of its quality is based on isopleths and isothermal sections from the same primary sources.

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