Compositional Analysis of Extracellular Aggregates in the Eyes of Patients With Exfoliation Syndrome and Exfoliation Glaucoma.

Purpose: Exfoliation syndrome (XFS) is a condition characterized by the production of insoluble fibrillar aggregates (exfoliation material; XFM) in the eye and elsewhere. Many patients with XFS progress to exfoliation glaucoma (XFG), a significant cause of global blindness. We used quantitative mass spectrometry to analyze the composition of XFM in lens capsule specimens and in aqueous humor (AH) samples from patients with XFS, patients with XFG and unaffected individuals. Methods: Pieces of lens capsule and samples of AH were obtained with consent from patients undergoing cataract surgery. Tryptic digests of capsule or AH were analyzed by high-performance liquid chromatography-mass spectrometry and relative differences between samples were quantified using the tandem mass tag technique. The distribution of XFM on the capsular surface was visualized by SEM and super-resolution light microscopy. Results: A small set of proteins was consistently upregulated in capsule samples from patients with XFS and patients with XFG, including microfibril components fibrillin-1, latent transforming growth factor-ß-binding protein-2 and latent transforming growth factor-ß-binding protein-3. Lysyl oxidase-like 1, a cross-linking enzyme associated with XFS in genetic studies, was an abundant XFM constituent. Ligands of the transforming growth factor-ß superfamily were prominent, including LEFTY2, a protein best known for its role in establishing the embryonic body axis. Elevated levels of LEFTY2 were also detected in AH from patients with XFG, a finding confirmed subsequently by ELISA. Conclusions: This analysis verified the presence of suspected XFM proteins and identified novel components. Quantitative comparisons between patient samples revealed a consistent XFM proteome characterized by strong expression of fibrillin-1, lysyl oxidase-like-1, and LEFTY2. Elevated levels of LEFTY2 in the AH of patients with XFG may serve as a biomarker for the disease.

Heat treatment of soluble proteins isolated from human cataract lens leads to the formation of non-fibrillar amyloid-like protein aggregates.

The loss of crystallins solubility with aging and the formation of amyloid-like aggregates is considered the hallmark characteristic of cataract pathology. The present study was carried out to assess the effect of temperature on the soluble lens protein and the formation of protein aggregates with typical amyloid characteristics. The soluble fraction of lens proteins was subjected for heat treatment in the range of 40-60 °C, and the nature of protein aggregates was assessed by using Congo red (CR), thioflavin T (ThT), and 8-anilinonaphthalene-1-sulfonic acid (ANS) binding assays, circular dichroism (CD), Fourier-transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). The heat-treated protein samples displayed a substantial bathochromic shift (≈15 nm) in the CR's absorption maximum (λmax) and increased ThT and ANS binding. The heat treatment of lens soluble proteins results in the formation of nontoxic, ß-sheet rich, non-fibrillar, protein aggregates similar to the structures evident in the insoluble fraction of proteins isolated from the cataractous lens. The data obtained from the present study suggest that the exposure of soluble lens proteins to elevated temperature leads to the formation of non-fibrillar aggregates, establishing the role of amyloid in the heat-induced augmentation of cataracts pathology.

X-ray linear dichroic ptychography.

Biominerals such as seashells, coral skeletons, bone, and tooth enamel are optically anisotropic crystalline materials with unique nanoscale and microscale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Using Seriatopora aculeata coral skeleton as a model, here, we experimentally demonstrate X-ray linear dichroic ptychography and map the c-axis orientations of the aragonite (CaCO3) crystals. Linear dichroic phase imaging at the oxygen K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (<35°) and wide (>35°) c-axis angular spread in the coral samples. These X-ray ptychography results are corroborated by four-dimensional (4D) scanning transmission electron microscopy (STEM) on the same samples. Evidence of co-oriented, but disconnected, corallite subdomains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. We expect that the combination of X-ray linear dichroic ptychography and 4D STEM could be an important multimodal tool to study nano-crystallites, interfaces, nucleation, and mineral growth of optically anisotropic materials at multiple length scales.

Eye patches: Protein assembly of index-gradient squid lenses.

A parabolic relationship between lens radius and refractive index allows spherical lenses to avoid spherical aberration. We show that in squid, patchy colloidal physics resulted from an evolutionary radiation of globular S-crystallin proteins. Small-angle x-ray scattering experiments on lens tissue show colloidal gels of S-crystallins at all radial positions. Sparse lens materials form via low-valence linkages between disordered loops protruding from the protein surface. The loops are polydisperse and bind via a set of hydrogen bonds between disordered side chains. Peripheral lens regions with low particle valence form stable, volume-spanning gels at low density, whereas central regions with higher average valence gel at higher densities. The proteins demonstrate an evolved set of linkers for self-assembly of nanoparticles into volumetric materials.

Phosphorylation of αB-crystallin: Role in stress, aging and patho-physiological conditions.

BACKGROUND: αB-crystallin, once thought to be a lenticular protein, is ubiquitous and has critical roles in several cellular processes that are modulated by phosphorylation. Serine residues 19, 45 and 59 of αB-crystallin undergo phosphorylation. Phosphorylation of S45 is mediated by p44/42 MAP kinase, whereas S59 phosphorylation is mediated by MAPKAP kinase-2. Pathway involved in S19 phosphorylation is not known. SCOPE OF REVIEW: The review highlights the role of phosphorylation in (i) oligomeric structure, stability and chaperone activity, (ii) cellular processes such as apoptosis, myogenic differentiation, cell cycle regulation and angiogenesis, and (iii) aging, stress, cardiomyopathy-causing αB-crystallin mutants, and in other diseases. MAJOR CONCLUSIONS: Depending on the context and extent of phosphorylation, αB-crystallin seems to confer beneficial or deleterious effects. Phosphorylation alters structure, stability, size distribution and dynamics of the oligomeric assembly, thus modulating chaperone activity and various cellular processes. Phosphorylated αB-crystallin has a tendency to partition to the cytoskeleton and hence to the insoluble fraction. Low levels of phosphorylation appear to be protective, while hyperphosphorylation has negative implications. Mutations in αB-crystallin, such as R120G, Q151X and 464delCT, associated with inherited myofibrillar myopathy lead to hyperphosphorylation and intracellular inclusions. An ongoing study in our laboratory with phosphorylation-mimicking mutants indicates that phosphorylation of R120GαB-crystallin increases its propensity to aggregate. GENERAL SIGNIFICANCE: Phosphorylation of αB-crystallin has dual role that manifests either beneficial or deleterious consequences depending on the extent of phosphorylation and interaction with cytoskeleton. Considering that disease-causing mutants of αB-crystallin are hyperphosphorylated, moderation of phosphorylation may be a useful strategy in disease management. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Lanosterol reverses protein aggregation in cataracts.

The human lens is comprised largely of crystallin proteins assembled into a highly ordered, interactive macro-structure essential for lens transparency and refractive index. Any disruption of intra- or inter-protein interactions will alter this delicate structure, exposing hydrophobic surfaces, with consequent protein aggregation and cataract formation. Cataracts are the most common cause of blindness worldwide, affecting tens of millions of people, and currently the only treatment is surgical removal of cataractous lenses. The precise mechanisms by which lens proteins both prevent aggregation and maintain lens transparency are largely unknown. Lanosterol is an amphipathic molecule enriched in the lens. It is synthesized by lanosterol synthase (LSS) in a key cyclization reaction of a cholesterol synthesis pathway. Here we identify two distinct homozygous LSS missense mutations (W581R and G588S) in two families with extensive congenital cataracts. Both of these mutations affect highly conserved amino acid residues and impair key catalytic functions of LSS. Engineered expression of wild-type, but not mutant, LSS prevents intracellular protein aggregation of various cataract-causing mutant crystallins. Treatment by lanosterol, but not cholesterol, significantly decreased preformed protein aggregates both in vitro and in cell-transfection experiments. We further show that lanosterol treatment could reduce cataract severity and increase transparency in dissected rabbit cataractous lenses in vitro and cataract severity in vivo in dogs. Our study identifies lanosterol as a key molecule in the prevention of lens protein aggregation and points to a novel strategy for cataract prevention and treatment.

Amyloid fibrils from readily available sources: milk casein and lens crystallin proteins.

Amyloid fibrils are a highly ordered and robust aggregated form of protein structure in which the protein components are arranged in long fibrillar arrays comprised of ß-sheet. Because of these properties, along with their biocompatibility, amyloid fibrils have attracted much research attention as bionanomaterials, for example as template structures (in some cases following modification) that can be used as biosensors, encapsulators, and biomimetic materials. To use amyloid fibrils for such a range of applications will require them to be obtained relatively easily in large quantities. In this chapter, we describe methods for isolating crystallin and casein proteins from readily available sources that contain abundant protein, i.e., the eye lens and milk, respectively, and the subsequent conversion of these proteins into amyloid fibrils.

Crystalline structure and thermal property characterization of chitin from Antarctic krill (Euphausia superba).

Antarctic krill (Euphausia superba) has been widely studied and extensively recognized as a target for commercial fishing. In this study, Antarctic krill chitin was extracted from defatted Antarctic krill shell, and its crystalline structure and thermal properties were characterized by employing Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. Results showed that Antarctic krill chitin corresponded to the α-polymorph, and was composed of small, stable, and uniform microcrystals. The degree of N-deacetylation was 11.28 ± 0.86%. The d-spacings of Antarctic krill chitin were 9.78 Å and 4.63 Å at (020) and (110) planes. The crystalline sizes were 6.07 nm and 5.16 nm at (020) and (110) planes, respectively. The activation energy of the polysaccharide chain decomposition was 123.35 kJ/mol and the glass transition (T(g)) of Antarctic krill chitin was 164.96 °C.

Electron tomography of fiber cell cytoplasm and dense cores of multilamellar bodies from human age-related nuclear cataracts.

Human nuclear cataract formation is a multi-factorial disease with contributions to light scattering from many cellular sources that change their scattering properties over decades. The aging process produces aggregation of cytoplasmic crystallin proteins, which alters the protein packing and texture of the cytoplasm. Previous studies of the cytoplasmic texture quantified increases in density fluctuations in protein packing and theoretically predicted the corresponding scattering. Multilamellar bodies (MLBs) are large particles with a core of crystallin cytoplasm that have been suggested to be major sources of scattering in human nuclei. The core has been shown to condense over time such that the refractive index increases compared to the adjacent aged and textured cytoplasm. Electron tomography is used here to visualize the 3D arrangement of protein aggregates in aged and cataractous lens nuclear cytoplasm compared to the dense protein packing in the cores of MLBs. Thin sections, 70 nm thick, were prepared from epoxy-embedded human transparent donor lenses and nuclear cataracts. Tilt series were collected on an FEI T20 transmission electron microscope (TEM) operated at 200 kV using 15 nm gold particles as fiducial markers. Images were aligned and corrected with FEI software and reconstructed with IMOD and other software packages to produce animated tilt series and stereo anaglyphs. The 3D views of protein density showed the relatively uniform packing of proteins in aged transparent lens nuclear cytoplasm and less dense packing of aged cataractous cytoplasm where many low-density regions can be appreciated in the absence of the TEM projection artifacts. In contrast the cores of the MLBs showed a dense packing of protein with minimal density fluctuations. These observations support the conclusion that, during the nuclear cataract formation, alterations in protein packing are extensive and can result in pronounced density fluctuations. Aging causes the MLB cores to become increasingly different in their protein packing from the adjacent cytoplasm. These results support the hypothesis that the MLBs increase their scattering with age and nuclear cataract formation.

Multiple sites in αB-crystallin modulate its interactions with desmin filaments assembled in vitro.

The ß3- and ß8-strands and C-terminal residues 155-165 of αB-crystallin were identified by pin arrays as interaction sites for various client proteins including the intermediate filament protein desmin. Here we present data using 5 well-characterised αB-crystallin protein constructs with substituted ß3- and ß8-strands and with the C-terminal residues 155-165 deleted to demonstrate the importance of these sequences to the interaction of αB-crystallin with desmin filaments. We used electron microscopy of negatively stained samples to visualize increased interactions followed by sedimentation assays to quantify our observations. A low-speed sedimentation assay measured the ability of αB-crystallin to prevent the self-association of desmin filaments. A high-speed sedimentation assay measured αB-crystallin cosedimentation with desmin filaments. Swapping the ß8-strand of αB-crystallin or deleting residues 155-165 increased the cosedimentation of αB-crystallin with desmin filaments, but this coincided with increased filament-filament interactions. In contrast, substitution of the ß3-strand with the equivalent αA-crystallin sequences improved the ability of αB-crystallin to prevent desmin filament-filament interactions with no significant change in its cosedimentation properties. These data suggest that all three sequences (ß3-strand, ß8-strand and C-terminal residues 155-165) contribute to the interaction of αB-crystallin with desmin filaments. The data also suggest that the cosedimentation of αB-crystallin with desmin filaments does not necessarily correlate with preventing desmin filament-filament interactions. This important observation is relevant not only to the formation of the protein aggregates that contain both desmin and αB-crystallin and typify desmin related myopathies, but also to the interaction of αB-crystallin with other filamentous protein polymers.

Heat-induced quaternary transitions in hetero- and homo-polymers of alpha-crystallin.

PURPOSE: To compare the effects of heat incubation on the structure and function of native alpha-crystallin, urea denatured/renatured alpha-crystallin, and alphaA and alphaB-crystallin homo-polymers purified from bovine lenses. METHODS: Each of the alpha-crystallin samples were incubated for 1 h at temperatures ranging from 35 degrees C to 70 degrees C. After heat incubation structural perturbations in each of the samples were studied using non-denaturing gel electrophoresis, transmission electron microscopy (TEM) and far-UV circular dichroism. The chaperone-like activity of each of the heat-treated samples was measured using the DTT induced insulin aggregation assay. RESULTS: The native alpha-crystallin samples showed secondary structure perturbations, an increase in aggregate size and asymmetry, and an increase in chaperone-like activity after heat incubation above 50 degrees C. The other three sample types showed secondary structure perturbations beginning at lower incubation temperatures, and a progressive decrease in chaperone-like activity with exposure to increasing temperatures. TEM showed all samples formed large asymmetric high molecular weight aggregates after incubation at 65 degrees C. CONCLUSIONS: The urea denaturation/renaturation of alpha-crystallin has been shown to result in the loss of a small amount of alpha-helix, but to have no effect on chaperone-like activity under standard test conditions. The present results indicate this lost alpha-helix may be responsible for the differential effects of heat incubation on the different forms of alpha-crystallin.

In vitro filament-like formation upon interaction between lens alpha-crystallin and betaL-crystallin promoted by stress.

PURPOSE: To determine whether alpha-crystallin is capable of forming filament-like structures with other members of the crystallin family. METHODS: Water-soluble crystallins were isolated from calf lenses and fractionated into alpha-, betaH-, betaL-, and gamma-crystallins according to standard procedures. Chaperone-like activity of alpha-crystallin was determined in control and UV-A-irradiated lenses by the heat-induced aggregation assay of betaL-crystallin. Protein samples from this assay were analyzed by electron microscopy. In vitro filament formation was examined by transmission immunoelectron microscopy using specific antibodies directed against the crystallins. Involvement of intermediate filament constituents was excluded by the results of Western blot analysis, which were all negative. Moreover, the in vitro amyloid fibril interaction test using thioflavin T (ThT) was also performed. RESULTS: At the supramolecular level heating at 60 degrees C has no effect on the morphologic appearance of alpha-crystallin as observed by transmission electron microscopy. Moreover alpha-crystallin obtained from UV-A-irradiated lenses shows a virtually identical shape. However, heating in the presence of betaL-crystallin results in the formation of filament-like alphabeta-hybrids as demonstrated by immunoelectron microscopy using specific antibodies directed either against alpha- or betaL-crystallin. Parallel experiments with alpha-crystallin derived from UV-A-irradiated lenses showed even more pronounced filamentous structures, compared with the controls. Nonetheless, we were able to show that the UV-light treatment affected the chaperone-like capacity of alpha-crystallin, as revealed by a diminished ability to inhibit in vitro denaturation of betaL-crystallin. To exclude the presence of cytoskeletal contamination in the crystallin preparations, vimentin antibodies were also tested. These latter experiments were negative. The filamentous nature of the hybrids was further confirmed by the results obtained with the ThT assay earlier applied for the detection of amyloid fibrils. CONCLUSIONS: Crystallin hybrids have previously been detected in the water-soluble lens crystallin fraction. Our findings indicate that such endogenous hybrids, formerly called "rods," may result from stress-induced interaction between alpha-crystallin and other lens constituents such as betaL-crystallin. Because the hybrid formation is enhanced when alpha-crystallin from UV-A-irradiated lenses is used as one of the two components of the hybrid, one can only speculate that this formation may be one of the factors leading to UV-A cataract.

Small heat-shock protein structures reveal a continuum from symmetric to variable assemblies.

The small heat-shock proteins (sHSPs) form a diverse family of proteins that are produced in all organisms. They function as chaperone-like proteins in that they bind unfolded polypeptides and prevent uncontrolled protein aggregation. Here, we present parallel cryo-electron microscopy studies of five different sHSP assemblies: Methanococcus jannaschii HSP16.5, human alphaB-crystallin, human HSP27, bovine native alpha-crystallin, and the complex of alphaB-crystallin and unfolded alpha-lactalbumin. Gel-filtration chromatography indicated that HSP16.5 is the most monodisperse, while HSP27 and the alpha-crystallin assemblies are more polydisperse. Particle images revealed a similar trend showing mostly regular and symmetric assemblies for HSP16.5 particles and the most irregular assemblies with a wide range of diameters for HSP27. A symmetry test on the particle images indicated stronger octahedral symmetry for HSP16.5 than for HSP27 or the alpha-crystallin assemblies. A single particle reconstruction of HSP16.5, based on 5772 particle images with imposed octahedral symmetry, resulted in a structure that closely matched the crystal structure. In addition, the cryo-EM reconstruction revealed internal density presumably corresponding to the flexible 32 N-terminal residues that were not observed in the crystal structure. The N termini were found to partially fill the central cavity making it unlikely that HSP16.5 sequesters denatured proteins in the cavity. A reconstruction calculated without imposed symmetry confirmed the presence of at least loose octahedral symmetry for HSP16.5 in contrast to the other sHSPs examined, which displayed no clear overall symmetry. Asymmetric reconstructions for the alpha-crystallin assemblies, with an additional mass selection step during image processing, resulted in lower resolution structures. We interpret the alpha-crystallin reconstructions to be average representations of variable assemblies and suggest that the resolutions achieved indicate the degree of variability. Quaternary structural information derived from cryo-electron microscopy is related to recent EPR studies of the alpha-crystallin domain fold and dimer interface of alphaA-crystallin.

Molecular basis for the polymerization of octopus lens S-crystallin.

S-Crystallin from octopus lens has a tertiary structure similar to sigma-class glutathione transferase (GST). However, after isolation from the lenses, S-crystallin was found to aggregate more easily than sigma-GST. In vitro experiments showed that the lens S-crystallin can be polymerized and finally denatured at increasing concentration of urea or guanidinium chloride (GdmCl). In the intermediate concentrations of urea or GdmCl, the polymerized form of S-crystallin is aggregated, as manifested by the increase in light scattering and precipitation of the protein. There is a delay time for the initiation of polymerization. Both the delay time and rate of polymerization depend on the protein concentration. The native protein showed a maximum fluorescence emission spectrum at 341 nm. The GdmCl-denatured protein exhibited two fluorescence maxima at 310 nm and 358 nm, respectively, whereas the urea-denatured protein showed a fluorescence peak at 358 nm with a small peak at 310 nm. The fluorescence intensity was quenched. Monomers, dimers, trimers, and polymers of the native protein were observed by negative-stain electron microscopic analysis. The aggregated form, however, showed irregular structure. The aggregate was solubilized in high concentrations of urea or GdmCl. The redissolved denatured protein showed an identical fluorescence spectrum to the protein solution that was directly denatured with high concentrations of urea or GdmCl. The denatured protein was readily refolded to its native state by diluting with buffer solution. The fluorescence spectrum of the renatured protein solution was similar to that of the native form. The phase diagrams for the S-crystallin in urea and GdmCl were constructed. Both salt concentration and pH value of the solution affect the polymerization rate, suggesting the participation of ionic interactions in the polymerization. Comparison of the molecular models of the S-crystallin and sigma-GST suggests that an extra ion-pair between Asp-101 and Arg-14 in S-crystallin contributes to stabilizing the protomer. Furthermore, the molecular surface of S-crystallin has a protruding Lys-208 on one side and a complementary patch of aspartate residues (Asp-90, Asp-94, Asp-101, Asp-102, Asp-179, and Asp-180) on the other side. We propose a molecular model for the S-crystallin polymer in vivo, which involves side-by-side associations of Lys-208 from one protomer and the aspartate patch from another protomer that allows the formation of a polymeric structure spontaneously into a liquid crystal structure in the lens.

Correlation between the chaperone-like activity and aggregate size of alpha-crystallin with increasing temperature.

alpha-Crystallin, the major protein of the mammalian eye lens, is also found in the major tissues of the body, where one or the other of its two isoforms is characteristically expressed. Both isoform sequences are highly related to others of the small heat shock protein superfamily, leading to speculation about their functions in vivo outside of the lens. Tests of chaperone-like activity at 37 and 66 degrees C indicate that the protein can act to prevent the superaggregation of partially denatured proteins, but both alpha-crystallin aggregate size and shape are significantly altered with increasing temperature. Characterization of these changes indicates that secondary, tertiary, and quaternary structure are modified, with the latter effect especially striking above 50 degrees C. Furthermore, these changes appear to be irreversible when the temperature is returned to 25 or 37 degrees C. Functionally, the protein is effective in chaperone-like activity at all temperatures, but exhibits a somewhat increased capability after a cycle of heating and cooling. The results presented here indicate the heat-induced formation of high-molecular-weight aggregates of alpha-crystallin is a slow progressive process. The increased activity of these aggregates suggests that chaperone-like activity depends in part on the packing parameters of the aggregate and on conformation of the subunit within that aggregate.

Review: resolution issues in single-particle reconstruction.

Specific factors that affect the resolution of single-particle reconstructions are discussed. We present reconstructions of six particles (DNA-dependent protein kinase catalytic subunit, alphaB-crystallin, the ribonucleoprotein vault, hepatitis A virus, adenovirus type 2, and the adenovirus type 12/alpha(v)beta5 integrin complex), which have a variety of symmetries (asymmetric to 60-fold) and a wide range of molecular masses (470 kDa to 150 MDa). In the case of icosahedral viruses, we have found that applying a "soft" mask to remove regions of disordered density improves the resolution given by the Fourier shell correlation 0.5 criterion. This masking procedure is also useful during refinement to improve the quality of the reference model and thus aid in precise alignment of the particle images. For asymmetric particles, we note that image classification, although often a necessary step to generate a first reconstruction, can limit the achievable resolution. The diameter of the particle and the available computational power can also affect the resolution, as can structural variability within the particle.

Mutation R120G in alphaB-crystallin, which is linked to a desmin-related myopathy, results in an irregular structure and defective chaperone-like function.

alphaB-crystallin, a member of the small heat shock protein family, possesses chaperone-like function. Recently, it has been shown that a missense mutation in alphaB-crystallin, R120G, is genetically linked to a desmin-related myopathy as well as to cataracts [Vicart, P., Caron, A., Guicheney, P., Li, A., Prevost, M.-C., Faure, A., Chateau, D., Chapon, F., Tome, F., Dupret, J.-M., et al. (1998) Nat. Genet. 20, 92-95]. By using alpha-lactalbumin, alcohol dehydrogenase, and insulin as target proteins, in vitro assays indicated that R120G alphaB-crystallin had reduced or completely lost chaperone-like function. The addition of R120G alphaB-crystallin to unfolding alpha-lactalbumin enhanced the kinetics and extent of its aggregation. R120G alphaB-crystallin became entangled with unfolding alpha-lactalbumin and was a major portion of the resulting insoluble pellet. Similarly, incubation of R120G alphaB-crystallin with alcohol dehydrogenase and insulin also resulted in the presence of R120G alphaB-crystallin in the insoluble pellets. Far and near UV CD indicate that R120G alphaB-crystallin has decreased beta-sheet secondary structure and an altered aromatic residue environment compared with wild-type alphaB-crystallin. The apparent molecular mass of R120G alphaB-crystallin, as determined by gel filtration chromatography, is 1.4 MDa, which is more than twice the molecular mass of wild-type alphaB-crystallin (650 kDa). Images obtained from cryoelectron microscopy indicate that R120G alphaB-crystallin possesses an irregular quaternary structure with an absence of a clear central cavity. The results of this study show, through biochemical analysis, that an altered structure and defective chaperone-like function of alphaB-crystallin are associated with a point mutation that leads to a desmin-related myopathy and cataracts.