Moreover, this study revealed that the oligomeric structures of proteins with amino Ganetespib in vitro acid substitutions do not appear to be modified. Our data strongly suggest that different amino acids are involved in the thermostabilization of proteins and in membrane fluidity regulation and are localized in the α-crystallin domain. Bacteria use several mechanisms including heat shock protein (Hsp) synthesis to cope with environmental stress (Watson, 1990). Small Hsp (smHsp)

is a ubiquitous class of molecular chaperones that is similar in amino acid structure to the α-crystallins of the vertebrate eye lens (Narberhaus, 2002). They share monomer sizes ranging from 12 to 43 kDa. Although the smHsp family is the most diverse in terms of amino acid sequence, they are structurally subdivided into an N-terminal region of variable sequence and length, a conserved region of about

100 amino acids called the α-crystallin domain and a short C-terminal region (Krappe et al., 2002; Nakamoto & Vigh, 2007). SmHsps act as chaperones in vitro by binding to partially unfolded proteins in an ATP-independent manner, preventing their irreversible find more aggregation under heat shock (Haslbeck et al., 2005). This chaperone activity has also been demonstrated in Escherichia coli cells expressing an smHsp, Oshsp 16.9 of rice, by evaluating the thermostabilization of cellular proteins (Yeh et al., 1997). Previous biochemical studies with various smHsp family members Pyruvate dehydrogenase have shown a strong relationship between chaperone activity and oligomerization (Lentze et al., 2003; Giese & Vierling, 2004; Haslbeck et al., 2004). The active forms of smHsps are usually

large oligomers made up of an association of multiple subunits (MacRae, 2000; Narberhaus, 2002). The quaternary structure of α-crystallins is dynamic, which is reflected by a rapid subunit exchange (van den Oetelaar et al., 1990; Bova et al., 1997; Van Montfort et al., 2001). Under various stress conditions, the cytoplasmic membrane is the first sensitive target of damage in cells, as demonstrated by the leakage of intracellular substances and variation in membrane fluidity (Da Silveira et al., 2003). The cytoplasmic location of the smHsp is very variable and some are associated with cellular membrane fractions. This is indeed the case for the smHsp Lo18 from the lactic acid bacteria Oenococcus oeni, Hsp17 from Synechocystis PCC 6803, Sp21 from Stigmatella aurantiaca and Hsp12 of Saccharomyces cerevisiae (Lunsdorf et al., 1995; Jobin et al., 1997; Horvath et al., 1998; Sales et al., 2000). This type of localization has been related to a newly described function of the smHsp, i.e. its ability to interact with in vitro model lipid membranes and to increase lipid order in the liquid crystalline state (Török et al., 2001).