Characterization of Streptomyces albus 18-kilodalton heat shock-responsive protein

Abstract

In Streptomyces albus during the heat shock response, a small heat shock protein of 18 kDa is dramatically induced. This protein was purified, and internal sequences revealed that S. albus HSP18 showed a marked homology with proteins belonging to the family of small heat shock proteins. The corresponding gene was isolated and sequenced. DNA sequence analysis confirmed that the hsp18 gene product is an analog of the 18-kDa antigen of Mycobacterium leprae. No hsp18 mRNA could be detected at 30؇C, but transcription of this gene was strongly induced following heat shock. The transcription initiation site was determined by nuclease S1 protection. A typical streptomycete vegetative promoter sequence was identified upstream from the initiation site. Disruption mutagenesis of hsp18 showed that HSP18 is not essential for growth in the 30 to 42؇C temperature range. However, HSP18 is involved in thermotolerance at extreme temperatures.Streptomycetes are gram-positive, filamentous soil bacteria which undergo a complex cycle of morphological differentiation. They constitute an economically important group that produces a wide variety of unusual metabolites, including many of the naturally isolated antibiotics and other therapeutic agents.The heat shock response in streptomycetes has been studied in order to analyze the involvement of the heat shock proteins (HSPs) in morphological and physiological differentiation. Unrelated organisms, from bacteria and fungi to plants and animals, respond to a heat shock by the expression of very similar proteins. In prokaryotes, the best-characterized HSPs are DnaK and GroEL. The pleiotropic phenotypes of dnaK and groEL mutants and biochemical studies have demonstrated that these proteins have physiologically diverse functions due to their role as molecular chaperones; they mediate the correct assembly of other polypeptides (4). However, some organisms may have adapted HSPs for special requirements; HSPs in some prokaryotic and eukaryotic cells have been shown to play a role during development (11,12,20). Significantly, there are reports indicating induction of GroEL at a crucial point of the Streptomyces cell cycle (5).Two different groEL-like genes are present in Streptomyces albus (a common feature in Streptomyces species) (16). The S. albus groEL1 and groEL2 genes have been cloned, sequenced, and shown to be expressed. HSP56 is coded for by groEL2, and groEL1, which forms an operon with a groES-like gene, encodes HSP58.During a survey of the heat shock response in a set of 15 streptomycetes, the induction of a small HSP of 18 kDa was observed in S. albus (see Fig. 6) in our laboratory (7). An 18-kDa protein of an S. albus culture subjected to heat shock after normal growth was purified by a multistep procedure. N-terminal amino acid sequences were determined for the intact protein and internal peptides. The sequence of 49 amino acid residues was identical to that of the predicted product of the 5Ј end of the groEL1 gene.In the context of our continuing studies of the possible processin...

α-Crystallin-Type Heat Shock Proteins: Socializing Minichaperones in the Context of a Multichaperone Network

“…In contrast to E. coli, the deletion of hsp16.6 in Synechocystis sp. strain PCC 6803 resulted in a clear growth defect after heat shock treatment (177,178) and disruption of hsp18 in Streptomyces albus showed that the gene is required for thermotolerance at extreme temperatures (275). Thus, there is cumulative in vivo evidence that ␣-Hsps do play a physiological role in the protection against adverse conditions.…”

A Small Heat Shock Protein Cooperates with Heat Shock Protein 70 Systems to Reactivate a Heat-Denatured Protein

“…A considerable amount of data support a role for sHsps in the acquisition of thermotolerance to high temperature (Vierling, 1991(Vierling, , 1997Arrigo and Landry, 1994), although in some organisms or under some environmental conditions their function may be redundant with other cellular components (Petko and Lindquist, 1985;Servant and Mazodier, 1995;Wotton et al, 1996). Gain-of-function experiments in mammalian and Drosophila cells have shown that constitutive expression of sHsps confers some thermotolerance (Arrigo and Landry, 1994), and expression of plant sHsps in E. coli has also been reported to enhance hightemperature tolerance (Yeh et al, 1997;Soto et al, 1999).…”

Disruption of hspR, the repressor gene of the dnaK operon in Streptomyces albus G

“…Transcription of hsp18, encoding a small HSP (smHSP) highly expressed in S. albus, was also analysed (Servant and Mazodier, 1995). Its regulation is likely to be different from that of the groEL genes, as no CIRCE motif is present in the hsp18 promoter region.…”

“…albus RNA was extracted and Northern blotting was performed as previously described (Servant and Mazodier, 1995;Servant et al, 1994). Hybridization was carried out under highly stringent conditions and blots were washed with 0.5× SSC-0.1% SDS at 65ЊC.…”

“…Hybridization was carried out under highly stringent conditions and blots were washed with 0.5× SSC-0.1% SDS at 65ЊC. The probes used were a 750 bp Pst I fragment internal to S. coelicolor dnaK, eluted from pDML723, and the S. albus groES and hsp18 (Servant and Mazodier, 1995) genes.…”