Cell Stress and Chaperones (2012) 17:103–108 DOI 10.1007/s12192-011-0289-z ORIGINAL PAPER Thermotolerance and molecular chaperone function of the small heat shock protein HSP20 from hyperthermophilic archaeon, Sulfolobus solfataricus P2 Dong-Chol Li & Fan Yang & Bo Lu & Dian-Fu Chen & Wei-Jun Yang Received: 3 August 2011 / Accepted: 7 August 2011 / Published online: 20 August 2011 # The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Small heat shock proteins are ubiquitous in all three domains (Archaea, Bacteria and Eukarya) and possess molecular chaperone activity by binding to unfolded polypeptides and preventing aggregation of proteins in vitro. The functions of a small heat shock protein (S.so-HSP20) from the hyperthermophilic archaeon, Sulfolobus solfataricus P2 have not been described. In the present study, we used real-time polymerase chain reaction analysis to measure mRNA expression of S.so-HSP20 in S. solfataricus P2 and found that it was induced by temperatures that were substantially lower (60°C) or higher (80°C) than the optimal tempera- ture for S. solfataricus P2 (75°C). The expression of S.so- HSP20 mRNA was also up-regulated by cold shock (4°C). Escherichia coli cells expressing S.so-HSP20 showed greater thermotolerance in response to temperature shock (50°C, 4°C). By assaying enzyme activities, S.so-HSP20 was found to promote the proper folding of thermo- denatured citrate synthase and insulin B chain. These results suggest that S.so-HSP20 promotes thermotolerance and engages in chaperone-like activity during the stress response. Keywords sHSP . S.so-HSP20 . Sulfolobus solfataricus P2 D.-C. Li : F. Yang : B. Lu : D.-F. Chen : W.-J. Yang (*) College of Life Sciences, Zhejiang University and Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education, Hangzhou 310058, China e-mail: w_jyang@cls.zju.edu.cn D.-C. Li College of Life Sciences, Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea Introduction Archaea, one of the three major groups of life forms, are a highly diverse and abundant group that includes many “extremophiles” that thrive in harsh environments, such as hot springs, salt lakes, and submarine volcanic habitats (Madigan et al. 2000; Eckburg et al. 2003). Current knowledge on stress genes in archaea is considerably more limited than that for bacteria and eukaryotes. The stress response in archaea was first studied in 1980, but it was not until 1991 that an archaeal stress gene (hsp70) was first cloned and sequenced (Macario et al. 1991; Klumpp and Baumeister 1998). Since then, several studies have focused on stress genes and their expression in archaea (Macario et al. 1999), but many aspects of the archaeal stress response are yet to be studied. Sulfolobus solfataricus P2 is a very widely studied crenarchaeal organism that grows well in the low pH, high sulfur environment of volcanic hot springs. It is used as a model organism in archaeal research to study processes such as DNA replication, cell cycle, chromosomal integration, and RNA processing (She et al. 2001; Nicholas et al. 2004). The optimum temperature for S. solfataricus P2 is about 75°C, although it can live between 55°C and 90°C and in a pH range of 0.9–5.8, with its optimum pH being 2–3. The genome of S. solfataricus P2 was sequenced in 2001. It consists of a single circular chromosome of 2,992,245 base pairs, with 3,032 genes encoding 2,977 proteins (Ehrnsperger et al. 1997; Jakob et al. 1993; chang et al. 1996). Heat shock proteins (HSPs) are ubiquitously expressed cellular proteins that form a major, conserved protein family. Some HSPs are expressed constitutively under physiological conditions (Lindquist and Craig 1998; Haslbeck et al. 2005), while others are induced in response to chemical or physical stressors such as heat, heavy metals, oxidative stress, ethanol (Charles et al. 1996; Laszlo and Li 1993; Sun et al. 2007).