Characterization of a Small Heat Shock Protein, Mx Hsp16.6, of Myxococcus xanthus

Abstract

A number of heat shock proteins in Myxococcus xanthus were previously identified by two-dimensional (2D) gel electrophoresis. One of these protein was termed Mx Hsp16.6, and the gene encoding Mx Hsp16.6 was isolated. Mx Hsp16.6 consists of 147 amino acid residues and has an estimated molecular weight of 16,642, in accordance with the apparent molecular mass in the 2D gel. An ␣-crystallin domain, typically conserved in small heat shock proteins, was found in Mx Hsp16.6. Mx Hsp16.6 was not detected during normal vegetative growth but was immediately induced after heat shock. Expression of the hsp16.6 gene was not induced by other stresses, such as starvation, oxidation, and high osmolarity. Mx Hsp16.6 was mostly localized in particles formed after heat shock and precipitated by low-speed centrifugation. Furthermore, Mx Hsp16.6 was detected in highly electron-dense particles in heat-shocked cells by immunoelectron microscopy, suggesting that it forms large complexes with heat-denatured proteins. An insertion mutation in the hsp16.6 gene resulted in lower viability during heat shock and lower acquired thermotolerance. Therefore, it is likely that Mx Hsp16.6 plays critical roles in the heat shock response in M. xanthus.

The clpB gene is involved in the stress response of Myxococcus xanthus during vegetative growth and development

“…5). These genetic and phenotypic data are consistent with a role in M. xanthus for the predicted ClpB encoded by MXAN5092 as a stress-related chaperone protein involved in cellular tolerance of environmental stresses, as reported in other bacteria (Squires et al, 1991;Otani et al, 2005;Simão et al, 2005;Ventura et al, 2005;Meibom et al, 2008).…”

“…The M. xanthus genome encodes a large number of chaperones of different families (Goldman et al, 2006). Some of these chaperones have been shown to be induced in response to elevated temperature or other cellular stresses, and their functional roles in helping bacteria to cope with stressful conditions by inhibiting and reversing protein aggregation, as well as their involvement in the complex social behaviours of myxobacteria have been characterized (Weimer et al, 1998;Yang et al, 1998;Otani et al, 2005;. In this study we focused on MXAN5092, an M. xanthus ORF encoding a protein with strong sequence homology to ClpB (Fig.…”

“…The stress survival ability of the MXAN5092 mutant SW5001 was analysed as reported by Otani et al (2005). The wild-type strain and mutant were grown exponentially at 32 uC (OD 600 0.5-0.8).…”

“…To test the involvement of MXAN5092 in acquiring thermotolerance, the experiments were carried out as reported elsewhere (Otani et al, 2005;Simão et al, 2005). In brief, both the MXAN5092 mutant SW5001 and the wild-type strain DK1622 were grown exponentially in CYE liquid medium at 32 uC.…”

“…The genomic sequence of M. xanthus revealed multiple copies of chaperone-encoding genes (Goldman et al, 2006), and several of these genes have been shown to be involved in different cellular functions in M. xanthus under various stress conditions. Sglk, an hsp70 family protein, was reported to control the production of extracellular fibrils (Weimer et al, 1998;Yang et al, 1998), while a small heat-shock protein, Mx Hsp16.6, was identified and shown to play a critical role in the heat-shock response of M. xanthus (Otani et al, 2005). More recently, two copies of groEL genes were reported to be important in the stress response and multicellular social life cycle of M. xanthus .…”