The Myosin Chaperone UNC-45 Is Organized in Tandem Modules to Support Myofilament Formation in C. elegans

Gazda, Linn; Pokrzywa, Wojciech; Hellerschmied, Doris; Löwe, Thomas; Forné, Ignasi; Mueller-Planitz, Felix; Hoppe, Thorsten; Clausen, Tim

doi:10.1016/j.cell.2012.12.025

Cited by 101 publications

(219 citation statements)

References 72 publications

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“…In Sec72, it is positively charged (Fig. 1d), similarly to the TPR domains in Hop, Tom71, and Unc45, which all interact with the negatively charged C termini of chaperones (27)(28)(29). These features raise the possibility that the TPR domain of Sec72 also interacts with the negatively charged C terminus of a chaperone.…”

Section: Crystal Structure Of the Sec71-sec72 Complexmentioning

confidence: 94%

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Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

Tripathi

Mandon

Gilmore

et al. 2017

Journal of Biological Chemistry

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The biosynthesis of many eukaryotic proteins requires accurate targeting to and translocation across the endoplasmic reticulum membrane. Post-translational protein translocation in yeast requires both the Sec61 translocation channel, and a complex of four additional proteins: Sec63, Sec62, Sec71, and Sec72. The structure and function of these proteins are largely unknown. This pathway also requires the cytosolic Hsp70 protein Ssa1, but whether Ssa1 associates with the translocation machinery to target protein substrates to the membrane is unclear. Here, we use a combined structural and biochemical approach to explore the role of Sec71-Sec72 subcomplex in post-translational protein translocation. To this end, we report a crystal structure of the Sec71-Sec72 complex, which revealed that Sec72 contains a tetratricopeptide repeat (TPR) domain that is anchored to the endoplasmic reticulum membrane by Sec71. We also determined the crystal structure of this TPR domain with a C-terminal peptide derived from Ssa1, which suggests how Sec72 interacts with full-length Ssa1. Surprisingly, Ssb1, a cytoplasmic Hsp70 that binds ribosome-associated nascent polypeptide chains, also binds to the TPR domain of Sec72, even though it lacks the TPR-binding C-terminal residues of Ssa1. We demonstrate that Ssb1 binds through its ATPase domain to the TPR domain, an interaction that leads to inhibition of nucleotide exchange. Taken together, our results suggest that translocation substrates can be recruited to the Sec71-Sec72 complex either post-translationally through Ssa1 or cotranslationally through Ssb1.

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Section: Crystal Structure Of the Sec71-sec72 Complexmentioning

confidence: 94%

“…2c). We next tested whether Ssa1 binds the TPR domain of Sec72 via its C termini, akin to that seen for Hsp70 binding to other TPR domains such as Hop, Tom71, and Unc45 (27)(28)(29). A GST fusion of the C-terminal lid domain of Ssa1 interacted with the TPR domain (Fig.…”

Section: The Tpr Domain Of Sec72 Binds the C-terminal Tail Of Ssa1mentioning

confidence: 99%

Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

Tripathi

Mandon

Gilmore

et al. 2017

Journal of Biological Chemistry

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“…Strangely enough, while Unc45a is ubiquitously expressed and largely persists in differentiating C2C12 cells (48), the muscle-specific isoform Unc45b (48) appears to bind Hsp90 without isoform specificity (13). Nevertheless, it is noteworthy that Unc45 was linked to muscle differentiation and myosin assembly in the nematode Caenorhabditis elegans (55,56), an organism that has p23 but no Aarsd1 ortholog. Moreover, in an Unc45 mutant of the same organism, Hsp90 and other cochaperones are required for muscle integrity and motility (57).…”

Section: Discussionmentioning

confidence: 99%

A Remodeled Hsp90 Molecular Chaperone Ensemble with the Novel Cochaperone Aarsd1 Is Required for Muscle Differentiation

Echeverria

Briand

Picard

2016

Molecular and Cellular Biology

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Hsp90 is the ATP-consuming core component of a very abundant molecular chaperone machine that handles a substantial portion of the cytosolic proteome. Rather than one machine, it is in fact an ensemble of molecular machines, since most mammalian cells express two cytosolic isoforms of Hsp90 and a subset of up to 40 to 50 cochaperones and regulate their interactions and functions by a variety of posttranslational modifications. We demonstrate that the Hsp90 ensemble is fundamentally remodeled during muscle differentiation and that this remodeling is not just a consequence of muscle differentiation but possibly one of the drivers to accompany and to match the vast proteomic changes associated with this process. As myoblasts differentiate into myotubes, Hsp90␣ disappears and only Hsp90␤ remains, which is the only isoform capable of interacting with the novel musclespecific Hsp90 cochaperone Aarsd1L. Artificially maintaining Hsp90␣ or knocking down Aarsd1L expression interferes with the differentiation of C2C12 myotubes. During muscle differentiation, Aarsd1L replaces the more ubiquitous cochaperone p23 and in doing so dampens the activity of the glucocorticoid receptor, one of the Hsp90 clients relevant to muscle functions. This cochaperone switch protects muscle cells against the inhibitory effects of glucocorticoids and may contribute to preventing muscle wasting induced by excess glucocorticoids. H sp90 is a highly abundant molecular chaperone, including in nonstressed cells, which is required for the maturation, stability, activity, and/or degradation of a substantial portion of the proteome (1-5) (for a regularly updated list of Hsp90 interactors, see http://www.picard.ch/downloads/Hsp90interactors.pdf). To its clients, the Hsp90 dimer offers a moving platform whose complex choreography involves ATP hydrolysis, huge conformational changes, and dynamic interactions with a large cohort of cochaperones (3, 6-11). The cochaperones regulate and are part of the Hsp90 cycle (3,(8)(9)(10)(11), and some may act as client specificity factors (12, 13). With 40 to 50 cochaperones, far more have been reported (see http://www.picard.ch/downloads/Hsp90facts.pdf) than the ones that have been extensively characterized as interacting with Hsp90 as part of the core cycle. Moreover, Hsp90 and cochaperones are extensively regulated by posttranslational modifications (see, for example, references 14-17), and Hsp90 is present in excess over any individual cochaperone. Hence, the Hsp90 molecular chaperone machine constitutes in fact an ensemble of complexes. These complexes dynamically interchange and are fashioned by the cell specificity of signaling and cochaperone expression patterns.One of the most extensively characterized components of the Hsp90 core machinery is the cochaperone p23 (18-20), encoded by the PTGES3 gene in mammals. This small acidic protein binds and stabilizes the ATP-bound state of Hsp90 (19-23). p23 binding, which is disrupted by Hsp90 inhibitors competing with ATP and by hyperacetylation of Hsp90, promotes a ...

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“…This is consistent with recent evidence that the UNC45B protein function is part of a multimeric complex. 35,36 Gazda et al 36 have demonstrated that C. elegans UNC-45 forms linear protein chains that offer multiple binding sites for cooperating chaperones and client proteins. The backbone of the UNC-45 filament is composed of the tethered superhelix ARM1-8 and TPR1-3 unit, and the UCS domain extends away from the filament axis.…”

Section: Discussionmentioning

confidence: 99%

The myosin chaperone UNC45B is involved in lens development and autosomal dominant juvenile cataract

et al. 2014

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Genome-wide linkage analysis, followed by targeted deep sequencing, in a Danish multigeneration family with juvenile cataract revealed a region of chromosome 17 co-segregating with the disease trait. Affected individuals were heterozygous for two potentially protein-disrupting alleles in this region, in ACACA and UNC45B. As alterations of the UNC45B protein have been shown to affect eye development in model organisms, effort was focused on the heterozygous UNC45B missense mutation. UNC45B encodes a myosin-specific chaperone that, together with the general heat shock protein HSP90, is involved in myosin assembly. The mutation changes p.Arg805 to Trp in the UCS domain, an amino acid that is highly conserved from yeast to human. UNC45B is strongly expressed in the heart and skeletal muscle tissue, but here we show expression in human embryo eye and zebrafish lens. The zebrafish mutant steif, carrying an unc45b nonsense mutation, has smaller eyes than wild-type embryos and shows accumulation of nuclei in the lens. Injection of RNA encoding the human wild-type UNC45B protein into the steif homozygous embryo reduced the nuclei accumulation and injection of human mutant UNC45B cDNA in wild-type embryos resulted in development of a phenotype similar to the steif mutant. The p.Arg805Trp alteration in the mammalian UNC45B gene suggests that developmental cataract may be caused by a defect in non-muscle myosin assembly during maturation of the lens fiber cells. Keywords: congenital cataract; UNC45B; non-muscle myosin; epithelial lens cell; zebrafish steif mutant INTRODUCTION Congenital/infantile cataract (CC) is a developmental anomaly characterized by opacities in the crystal lens of the eye and is a common cause of restricted vision and blindness in children. Environmental and intrinsic factors are involved, including metabolic and genetic causes for CC. Mendelian forms of CC comprise a broad spectrum of syndromic and nonsyndromic phenotypes characterized by a set of associated ocular and/or systemic abnormalities. More than 35 loci, including at least 25 known genes, have been associated with nonsyndromic cataract, the majority showing autosomal dominant inheritance with high penetrance (ADCC). 1,2 Mutations in crystallins, particularly CRYAA, CRYBB2, and CRYGD and the connexin genes GJA3 and GJA8 comprise the largest group of loci causing ADCC, but mutations are also found in the membrane proteins MIP, LIM2, TMEM114 and CHMP4B, in cytoskeleton proteins (BSFP1 and BSFP2) and in transcription factors (HSF4 and MAF). 1,2 In a recent study, 3 we reported that these loci represented most of the causative mutations in 19 out of 28 unrelated Danish CC families. Among the unsolved families was one in which genome-wide linkage analysis revealed two candidate loci at 2q32.3-q33.3 and 17q11.2-q21.2, respectively. 3 The family comprised three generations with nine

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The Myosin Chaperone UNC-45 Is Organized in Tandem Modules to Support Myofilament Formation in C. elegans

Cited by 101 publications

References 72 publications

Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

A Remodeled Hsp90 Molecular Chaperone Ensemble with the Novel Cochaperone Aarsd1 Is Required for Muscle Differentiation

The myosin chaperone UNC45B is involved in lens development and autosomal dominant juvenile cataract

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