Subunit Exchange of Small Heat Shock Proteins

Bova, Michael P.; Mchaourab, Hassane S.; Han, Yun; Fung, Bernard K.-K.

doi:10.1074/jbc.275.2.1035

Cited by 221 publications

(192 citation statements)

References 88 publications

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“…3 Investigation of the time course of subunit exchange of HSP18.1 and HSP16.6 revealed that this process is temperaturedependent and is rapid at the optimal growth temperature for the organism from which the sHSP originated. At 0°C no subunit exchange was observed for HSP18.1 or HSP16.6, similar to results with vertebrate sHSPs at 3°C (19,21). At 22°C, a normal growth temperature for pea, subunit exchange of HSP18.1 was very rapid, going to completion between 15 and 30 min.…”

Section: Shsp-substrate Complexessupporting

confidence: 59%

“…Subunit exchange for Synechocystis HSP16.6 was complete within ϳ1 h at 30°C, the optimal growth temperature for the cyanobacterium, but was significantly reduced at 22°C, taking over 3 h to reach completion. Subunit exchange for both proteins is much faster than what has been observed for mammalian ␣A-crystallin and ␣B-crystallin, which required ϳ4 h to reach equilibrium at 37°C and was even slower at lower temperatures (19,21). Previous experiments also showed that HSP16.5 from M. jannaschii does not exhibit significant subunit exchange until over 50°C, consistent with the hyperthermophilic lifestyle of this organism.…”

Section: Shsp-substrate Complexesmentioning

confidence: 49%

“…The only noticeable difference between wild-type and strep-tagged sHSPs was a small increase in the apparent size of HSP18.1⅐Luc complexes. From the crystal structure and other evidence, the C-terminal extension has been shown to be important for oligomerization, but there is no evidence that it interacts with substrate (5,7,21,37,38). The size differences between complexes made with wild type alone and those made with some amount of strep-tagged HSP18.1 indicate that the C-terminal extension may play a role in structuring complexes.…”

Section: Shsp-substrate Complexesmentioning

confidence: 98%

“…Rapid subunit exchange between sHSP oligomers has been observed for a number of sHSPs (11, 19 -22). Fluorescence energy transfer experiments conducted with the polydisperse mammalian ␣A-and ␣B-crystallin and HSP27 revealed fully exchanged oligomers within a few hours at 37°C (19,21). Even the well ordered wheat and Methanococcus sHSP oligomers exhibit rapid subunit dissociation and reassociation (11,22).…”

mentioning

confidence: 99%

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Interactions between Small Heat Shock Protein Subunits and Substrate in Small Heat Shock Protein-Substrate Complexes

Friedrich

Giese

Buan³

et al. 2004

Journal of Biological Chemistry

105

114

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Small heat shock proteins (sHSPs) are dynamic oligomeric proteins that bind unfolding proteins and protect them from irreversible aggregation. This binding results in the formation of sHSP-substrate complexes from which substrate can later be refolded. Interactions between sHSP and substrate in sHSP-substrate complexes and the mechanism by which substrate is transferred to ATP-dependent chaperones for refolding are poorly defined. We have established C-terminal affinity-tagged sHSPs from a eukaryote (pea HSP18.1) and a prokaryote (Synechocystis HSP16.6) as tools to investigate these issues. We demonstrate that sHSP subunit exchange for HSP18.1 and HSP16.6 is temperature-dependent and rapid at the optimal growth temperature for the organism of origin. Increasing the ratio of sHSP to substrate during substrate denaturation decreased sHSP-substrate complex size, and accordingly, addition of substrate to pre-formed sHSP-substrate complexes increased complex size. However, the size of pre-formed sHSP-substrate complexes could not be reduced by addition of more sHSP, and substrate could not be observed to transfer to added sHSP, although added sHSP subunits continued to exchange with subunits in sHSPsubstrate complexes. Thus, although some number of sHSP subunits within complexes remain dynamic and may be important for complex structure/solubility, association of substrate with the sHSP does not appear to be similarly dynamic. These observations are consistent with a model in which ATP-dependent chaperones associate directly with sHSP-bound substrate to initiate refolding. Small heat shock proteins (sHSPs)1 are ubiquitous stress proteins of 12-42 kDa that share a conserved C-terminal domain of ϳ100 amino acids (the ␣-crystallin domain) (1). The conserved ␣-crystallin domain is flanked by a variable length non-conserved N-terminal arm and a short C-terminal extension. In vivo and in vitro sHSP monomers assemble into native oligomers of 9 to Ͼ30 subunits, depending on the specific sHSP (2). sHSPs and the related vertebrate ␣-crystallins are proposed to function as molecular chaperones by preventing irreversible aggregation and insolubilization of denatured proteins (3-11). Many experiments have shown that sHSPs and ␣-crystallins have a large binding capacity for a variety of heat and chemically denatured model protein substrates (8,10,(12)(13)(14)(15). The models for sHSP function have been extended to suggest that substrates in sHSP-substrate complexes (here after referred to as "complexes") are held in a folding competent state, such that substrates can be reactivated by the ATP-dependent chaperone HSP70 (DnaK) and its respective co-chaperones (6, 9, 13, 14, 16).The x-ray structures of HSP16.5 from Methanococcus jannaschii, a 24-subunit oligomer (17), and HSP16.9 from Triticum aestivum (wheat), a 12-subunit oligomer (17, 18), reveal common features of sHSP structure. Despite limited sequence identity, these structures have a 1.5-Å root mean square difference between C-␣ atoms in the conserved ␣-crystallin domain, whic...

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Section: Shsp-substrate Complexessupporting

confidence: 59%

Section: Shsp-substrate Complexesmentioning

confidence: 49%

Section: Shsp-substrate Complexesmentioning

confidence: 98%

mentioning

confidence: 99%

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Interactions between Small Heat Shock Protein Subunits and Substrate in Small Heat Shock Protein-Substrate Complexes

Friedrich

Giese

Buan³

et al. 2004

Journal of Biological Chemistry

105

114

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“…4 The flexibility might also be an essential property enabling variable sizes and compositions of the multimeric complex of ␣B-crystallin and yielding mixed sHSP species (i.e. ␣A-crystallin, ␣B-crystallin, and HSP27) in a single hetero-oligomeric complex (44). It should be stressed that the potential flexibility of the protein is problematic for crystallographic analysis but not for solution scattering modeling (the experimental scattering pattern corresponds to an average position of the monomers).…”

Section: Discussionmentioning

confidence: 99%

A Novel Quaternary Structure of the Dimeric α-Crystallin Domain with Chaperone-like Activity

Feil¹,

Malfois²,

Hendle³

et al. 2001

Journal of Biological Chemistry

105

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␣B-crystallin, a member of the small heat-shock protein family and a major eye lens protein, is a high molecular mass assembly and can act as a molecular chaperone. We report a synchrotron radiation x-ray solution scattering study of a truncation mutant from the human ␣B-crystallin (␣B57-157), a dimeric protein that comprises the ␣-crystallin domain of the ␣B-crystallin and retains a significant chaperone-like activity. According to the sequence analysis (more than 23% identity), the monomeric fold of the ␣-crystallin domain should be close to that of the small heat-shock protein from Methanococcus jannaschii (MjHSP16.5). The theoretical scattering pattern computed from the crystallographic model of the dimeric MjHSP16.5 deviates significantly from the experimental scattering by the ␣-crystallin domain, pointing to different quaternary structures of the two proteins. A rigid body modeling against the solution scattering data yields a model of the ␣-crystallin domain revealing a new dimerization interface. The latter consists of a strand-turn-strand motif contributed by each of the monomers, which form a four-stranded, antiparallel, intersubunit composite ␤-sheet. This model agrees with the recent spin labeling results and suggests that the ␣B-crystallin is composed by flexible building units with an extended surface area. This flexibility may be important for biological activity and for the formation of ␣B-crystallin complexes of variable sizes and compositions.␣A-and ␣B-crystallin, which share 54% amino acid sequence identity, build the subunits of ␣-crystallin, a major eye lens protein, comprising up to 40% of the total lens proteins. The structural function of the ␣-crystallin is to assist in maintaining transparency in the lens (1). The chaperone-like function of ␣B-crystallin helps to avoid formation of large light-scattering aggregates and possibly helps to prevent cataract in the lens. Moreover, neurodegenerative diseases, ischemia, or multiple sclerosis lead to an overexpression of this protein, which makes it an object of special medical interest (2).The ␣-crystallin as well as other mammalian small heat-shock proteins (sHSPs)1 form large globular complexes with a diameter of about 10 -25 nm. Cryoelectron microscopy and image analysis revealed that ␣B-crystallin is a hollow spherical shell with variable quaternary structure (3), and a frequent exchange of subunits between the particles was observed. The chaperone activity of ␣B-crystallin is associated with partial perturbation of the substrate protein tertiary structure, leading to a multimeric molten globule-like state with increased hydrophobicity (4, 5). The exposed hydrophobic regions of ␣-crystallin interact with substrate proteins possessing an increased surface hydrophobicity but a low degree of unfolding (6).The molecular structure and subunit interactions in ␣-crystallin have long been under investigation. The stretches of residues promoting formation of lower or higher molecular weight ␣-crystallin oligomers have been identified. Upon additio...

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Crystallins

Jong¹,

Lubsen²

2006

Encyclopedia of Life Sciences

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‘Crystallins’ were originally designated as the characteristic eye lens protein constituents, but several of them are now known to function also in other tissues. In humans, three types of crystallins are distinguished (α‐, β‐ and γ‐crystallins), which together make up more than 90% of the water‐soluble lens protein. Additional and unrelated types of crystallins are present in other vertebrates.

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Subunit Exchange of Small Heat Shock Proteins

Cited by 221 publications

References 88 publications

Interactions between Small Heat Shock Protein Subunits and Substrate in Small Heat Shock Protein-Substrate Complexes

Interactions between Small Heat Shock Protein Subunits and Substrate in Small Heat Shock Protein-Substrate Complexes

A Novel Quaternary Structure of the Dimeric α-Crystallin Domain with Chaperone-like Activity

Crystallins

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