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Muranova LK, Strelkov SV, Gusev NB. Effect of cataract-associated mutations in the N-terminal domain of αB-crystallin (HspB5). Exp Eye Res 2020; 197:108091. [PMID: 32533979 DOI: 10.1016/j.exer.2020.108091] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 05/08/2020] [Accepted: 05/28/2020] [Indexed: 11/18/2022]
Abstract
Physico-chemical properties of three cataract-associated missense mutants of αB-crystallin (HspB5) (R11H, P20S, R56W) were analyzed. The oligomers formed by the R11H mutant were smaller, whereas the oligomers of the P20S and R56W mutants were larger than those of the wild-type protein. The P20S mutant possessed lower thermal stability than the wild-type HspB5 or two other HspB5 mutants. All HspB5 mutants were able to form heterooligomeric complexes with αA-crystallin (HspB4), a genuine component of eye lens. However, the P20S and R56W mutants were less effective in the formation of these complexes and properties of heterooligomeric complexes formed by these mutants and HspB4 and analyzed by ion-exchange chromatography were different from those formed by the wild-type HspB5 and HspB4. All HspB5 variants also heterooligomerized with another partner protein, HspB6. Specifically for the P20S mutant forming two distinct sizes of homooligomers, only the smaller homooligomer population was able to interact with HspB6. P20S and R56W mutants possessed lower chaperone-like activity than the wild-type HspB5 when UV-irradiated βL-crystallin was used as a model substrate. Importantly, all three mutations are localized in three earlier postulated short α-helical regions present in the N-terminal domain of αB-crystallin. These observations suggest an important structural and functional role of these regions. Correspondingly, therein localized mutations ultimately result in clinically relevant cataracts.
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Affiliation(s)
- Lydia K Muranova
- Department of Biochemistry, School of Biology, Moscow State University, Moscow, 119991, Russian Federation
| | - Sergei V Strelkov
- Laboratory of Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, 3000, Belgium
| | - Nikolai B Gusev
- Department of Biochemistry, School of Biology, Moscow State University, Moscow, 119991, Russian Federation.
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Haslbeck M, Weinkauf S, Buchner J. Small heat shock proteins: Simplicity meets complexity. J Biol Chem 2018; 294:2121-2132. [PMID: 30385502 DOI: 10.1074/jbc.rev118.002809] [Citation(s) in RCA: 172] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Small heat shock proteins (sHsps) are a ubiquitous and ancient family of ATP-independent molecular chaperones. A key characteristic of sHsps is that they exist in ensembles of iso-energetic oligomeric species differing in size. This property arises from a unique mode of assembly involving several parts of the subunits in a flexible manner. Current evidence suggests that smaller oligomers are more active chaperones. Thus, a shift in the equilibrium of the sHsp ensemble allows regulating the chaperone activity. Different mechanisms have been identified that reversibly change the oligomer equilibrium. The promiscuous interaction with non-native proteins generates complexes that can form aggregate-like structures from which native proteins are restored by ATP-dependent chaperones such as Hsp70 family members. In recent years, this basic paradigm has been expanded, and new roles and new cofactors, as well as variations in structure and regulation of sHsps, have emerged.
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Affiliation(s)
- Martin Haslbeck
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
| | - Sevil Weinkauf
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
| | - Johannes Buchner
- From the Department of Chemie and Center for Integrated Protein Science, Technische Universität München, Lichtenbergstrasse 4, 85 748 Garching, Germany
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The Role of the Arginine in the Conserved N-Terminal Domain RLFDQxFG Motif of Human Small Heat Shock Proteins HspB1, HspB4, HspB5, HspB6, and HspB8. Int J Mol Sci 2018; 19:ijms19072112. [PMID: 30036999 PMCID: PMC6073470 DOI: 10.3390/ijms19072112] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Revised: 07/14/2018] [Accepted: 07/17/2018] [Indexed: 11/17/2022] Open
Abstract
Although the N-terminal domain of vertebrate small heat shock proteins (sHsp) is poorly conserved, it contains a core motif preserved in many members of the sHsp family. The role of this RLFDQxFG motif remains elusive. We analyzed the specific role of the first arginine residue of this conserved octet sequence in five human sHsps (HspB1, HspB4, HspB5, HspB6, and HspB8). Substitution of this arginine with an alanine induced changes in thermal stability and/or intrinsic fluorescence of the related HspB1 and HspB8, but yielded only modest changes in the same biophysical properties of HspB4, HspB5, and HspB6 which together belong to another clade of vertebrate sHsps. Removal of the positively charged Arg side chain resulted in destabilization of the large oligomers of HspB1 and formation of smaller size oligomers of HspB5. The mutation induced only minor changes in the structure of HspB4 and HspB6. In contrast, the mutation in HspB8 was accompanied by shifting the equilibrium from dimers towards the formation of larger oligomers. We conclude that the RLFDQxFG motif plays distinct roles in the structure of several sHsp orthologs. This role correlates with the evolutionary relationship of the respective sHsps, but ultimately, it reflects the sequence context of this motif.
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Heirbaut M, Lermyte F, Martin EM, Beelen S, Sobott F, Strelkov SV, Weeks SD. Specific sequences in the N-terminal domain of human small heat-shock protein HSPB6 dictate preferential hetero-oligomerization with the orthologue HSPB1. J Biol Chem 2017; 292:9944-9957. [PMID: 28487364 DOI: 10.1074/jbc.m116.773515] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 04/20/2017] [Indexed: 12/17/2022] Open
Abstract
Small heat-shock proteins (sHSPs) are a conserved group of molecular chaperones with important roles in cellular proteostasis. Although sHSPs are characterized by their small monomeric weight, they typically assemble into large polydisperse oligomers that vary in both size and shape but are principally composed of dimeric building blocks. These assemblies can include different sHSP orthologues, creating additional complexity that may affect chaperone activity. However, the structural and functional properties of such hetero-oligomers are poorly understood. We became interested in hetero-oligomer formation between human heat-shock protein family B (small) member 1 (HSPB1) and HSPB6, which are both highly expressed in skeletal muscle. When mixed in vitro, these two sHSPs form a polydisperse oligomer array composed solely of heterodimers, suggesting preferential association that is determined at the monomer level. Previously, we have shown that the sHSP N-terminal domains (NTDs), which have a high degree of intrinsic disorder, are essential for the biased formation. Here we employed iterative deletion mapping to elucidate how the NTD of HSPB6 influences its preferential association with HSPB1 and show that this region has multiple roles in this process. First, the highly conserved motif RLFDQXFG is necessary for subunit exchange among oligomers. Second, a site ∼20 residues downstream of this motif determines the size of the resultant hetero-oligomers. Third, a region unique to HSPB6 dictates the preferential formation of heterodimers. In conclusion, the disordered NTD of HSPB6 helps regulate the size and stability of hetero-oligomeric complexes, indicating that terminal sHSP regions define the assembly properties of these proteins.
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Affiliation(s)
- Michelle Heirbaut
- From the Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, 3000 Leuven, Belgium
| | - Frederik Lermyte
- the Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, 2020 Antwerp, Belgium, and
| | - Esther M Martin
- the Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, 2020 Antwerp, Belgium, and.,the Astbury Centre for Structural Molecular Biology and
| | - Steven Beelen
- From the Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, 3000 Leuven, Belgium
| | - Frank Sobott
- the Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, 2020 Antwerp, Belgium, and.,the Astbury Centre for Structural Molecular Biology and.,School of Molecular and Cellular Biology, University of Leeds, LS2 9JT, United Kingdom
| | - Sergei V Strelkov
- From the Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, 3000 Leuven, Belgium,
| | - Stephen D Weeks
- From the Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, 3000 Leuven, Belgium,
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Heirbaut M, Lermyte F, Martin EM, Beelen S, Verschueren T, Sobott F, Strelkov SV, Weeks SD. The preferential heterodimerization of human small heat shock proteins HSPB1 and HSPB6 is dictated by the N-terminal domain. Arch Biochem Biophys 2016; 610:41-50. [PMID: 27717639 DOI: 10.1016/j.abb.2016.10.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 09/13/2016] [Accepted: 10/03/2016] [Indexed: 01/13/2023]
Abstract
Small heat shock proteins are ATP-independent molecular chaperones. Their function is to bind partially unfolded proteins under stress conditions. In vivo, members of this chaperone family are known to preferentially assemble together forming large, polydisperse heterooligomers. The exact molecular mechanisms that drive specific heteroassociation are currently unknown. Here we study the oligomers formed between human HSPB1 and HSPB6. Using small-angle X-ray scattering we could characterize two distinct heterooligomeric species present in solution. By employing native mass spectrometry we show that such assemblies are formed purely from heterodimeric building blocks, in line with earlier cross-linking studies. Crucially, a detailed analysis of truncation variants reveals that the preferential association between these two sHSPs is solely mediated by their disordered N-terminal domains.
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Affiliation(s)
- Michelle Heirbaut
- Laboratory for Biocrystallography, Dept. of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium
| | - Frederik Lermyte
- Biomolecular and Analytical Mass Spectrometry Group, Dept. of Chemistry, University of Antwerp, Belgium; Centre for Proteomics, University of Antwerp, Belgium
| | - Esther M Martin
- Biomolecular and Analytical Mass Spectrometry Group, Dept. of Chemistry, University of Antwerp, Belgium
| | - Steven Beelen
- Laboratory for Biocrystallography, Dept. of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium
| | - Tim Verschueren
- Biomolecular and Analytical Mass Spectrometry Group, Dept. of Chemistry, University of Antwerp, Belgium
| | - Frank Sobott
- Biomolecular and Analytical Mass Spectrometry Group, Dept. of Chemistry, University of Antwerp, Belgium
| | - Sergei V Strelkov
- Laboratory for Biocrystallography, Dept. of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium.
| | - Stephen D Weeks
- Laboratory for Biocrystallography, Dept. of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium.
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