α-Crystallins in the Vertebrate Eye Lens: Complex Oligomers and Molecular Chaperones

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Marc A. Sprague-Piercy ◽  
Megan A. Rocha ◽  
Ashley O. Kwok ◽  
Rachel W. Martin
Keyword(s):  
Posttranslational Modifications ◽  
Eye Lens ◽  
Annual Review ◽  
Publication Date ◽  
Binding Modes ◽  
Cryo Electron Microscopy ◽  
Αb Crystallin ◽  
C And N ◽  
Shock Proteins ◽  
Vertebrate Eye

α-Crystallins are small heat-shock proteins that act as holdase chaperones. In humans, αA-crystallin is expressed only in the eye lens, while αB-crystallin is found in many tissues. α-Crystallins have a central domain flanked by flexible extensions and form dynamic, heterogeneous oligomers. Structural models show that both the C- and N-terminal extensions are important for controlling oligomerization through domain swapping. α-Crystallin prevents aggregation of damaged β- and γ-crystallins by binding to the client protein using a variety of binding modes. α-Crystallin chaperone activity can be compromised by mutation or posttranslational modifications, leading to protein aggregation and cataract. Because of their high solubility and their ability to form large, functional oligomers, α-crystallins are particularly amenable to structure determination by solid-state NMR and solution NMR, as well as cryo-electron microscopy. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 72 is April 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals The Yin and Yang of Histone Marks in Transcription

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Paul B. Talbert ◽  
Steven Henikoff
Keyword(s):  
Posttranslational Modifications ◽  
Human Genetics ◽  
Annual Review ◽  
Publication Date ◽  
Histone Marks ◽  
The Core ◽  
Core Histones ◽  
Yin And Yang ◽  
Transcriptional State ◽  
Histone Core

Nucleosomes wrap DNA and impede access for the machinery of transcription. The core histones that constitute nucleosomes are subject to a diversity of posttranslational modifications, or marks, that impact the transcription of genes. Their functions have sometimes been difficult to infer because the enzymes that write and read them are complex, multifunctional proteins. Here, we examine the evidence for the functions of marks and argue that the major marks perform a fairly small number of roles in either promoting transcription or preventing it. Acetylations and phosphorylations on the histone core disrupt histone-DNA contacts and/or destabilize nucleosomes to promote transcription. Ubiquitylations stimulate methylations that provide a scaffold for either the formation of silencing complexes or resistance to those complexes, and carry a memory of the transcriptional state. Tail phosphorylations deconstruct silencing complexes in particular contexts. We speculate that these fairly simple roles form the basis of transcriptional regulation by histone marks. Expected final online publication date for the Annual Review of Genomics and Human Genetics Volume 22 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Structural and functional studies of D109A human αB-crystallin contributing to the development of cataract and cardiomyopathy diseases

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0260306
Author(s):  
Mahtab Hafizi ◽  
Natalia A. Chebotareva ◽  
Maryam Ghahramani ◽  
Faezeh Moosavi-Movahedi ◽  
Seyed Hossein Khaleghinejad ◽  
...  
Keyword(s):  
Heat Shock ◽  
Amyloid Fibrils ◽  
Eye Lens ◽  
Protein Oligomerization ◽  
Salt Bridges ◽  
Contributing Factors ◽  
Thermal Stabilities ◽  
Functional Studies ◽  
Αb Crystallin ◽  
Shock Proteins

αB-crystallin (heat shock protein β5/HSPB5) is a member of the family of small heat shock proteins that is expressed in various organs of the human body including eye lenses and muscles. Therefore, mutations in the gene of this protein (CRYAB) might have many pathological consequences. A new mutation has recently been discovered in the α-crystallin domain of this chaperone protein which replaces aspartate 109 with alanine (D109A). This mutation can cause myofibrillar myopathy (MFM), cataracts, and cardiomyopathy. In the current study, several spectroscopic and microscopic analyses, as well as gel electrophoresis assessment were applied to elucidate the pathogenic contribution of human αB-crystallin bearing D109A mutation in development of eye lens cataract and myopathies. The protein oligomerization, chaperone-like activity and chemical/thermal stabilities of the mutant and wild-type protein were also investigated in the comparative assessments. Our results suggested that the D109A mutation has a significant impact on the important features of human αB-crystallin, including its structure, size of the protein oligomers, tendency to form amyloid fibrils, stability, and chaperone-like activity. Given the importance of aspartate 109 in maintaining the proper structure of the α-crystallin domain, its role in the dimerization and chaperone-like activity, as well as preserving protein stability through the formation of salt bridges; mutation at this important site might have critical consequences and can explain the genesis of myopathy and cataract disorders. Also, the formation of large light-scattering aggregates and disruption of the chaperone-like activity by D109A mutation might be considered as important contributing factors in development of the eye lens opacity.

Mutation of COOH-terminal lysines in overexpressed αB- crystallin abrogates ischemic protection in cardiomyocytes

2002 ◽  
Vol 283 (1) ◽  
pp. H85-H91 ◽  
Author(s):  
Jody L. Martin ◽  
Wolfgang F. Bluhm ◽  
Huaping He ◽  
Ruben Mestril ◽  
Wolfgang H. Dillmann
Keyword(s):  
Posttranslational Modifications ◽  
Protein A ◽  
Proper Function ◽  
Enzyme Release ◽  
Wild Type ◽  
Native Page ◽  
Naturally Occurring ◽  
Αb Crystallin ◽  
Shock Proteins ◽  
Ischemic Stress

High levels of αB-crystallin are present in the cardiomyocyte, yet little is understood about the function and importance of this protein. Like many other small heat shock proteins, αB-crystallin forms large oligomeric complexes whose size can be regulated by posttranslational modifications. The size of these complexes can modify the function of the protein. A naturally occurring COOH-terminal mutant has many detrimental effects in the lens of the eye and altered oligomerization. Therefore, we mutated the two COOH-terminal lysines of αB-crystallin to glycines (K174/175G) and adenovirally mounted them to transduce cardiomyocytes. We analyzed the effect of this mutation on oligomerization, microtubular stabilization, and ischemic outcome. A nearly 45% downward shift in complex size was observed with the mutant by native PAGE followed by immunoblotting. The overexpressed protein no longer protected the tubulin cytoskeleton against ischemic stress by confocal analysis. The mutant caused a 30% increase in cytosolic enzyme release with ischemia compared with control, whereas a 33% decrease was associated with wild-type αB-crystallin overexpression. We conclude that the COOH terminus of αB-crystallin is crucial to its proper function.

Preparing Better Samples for Cryo–Electron Microscopy: Biochemical Challenges Do not End with Isolation and Purification

2021 ◽  
Vol 90 (1) ◽  
Author(s):  
Robert M. Glaeser
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Effective Control ◽  
Annual Review ◽  
Publication Date ◽  
Biological Macromolecules ◽  
Isolation And Purification ◽  
Cryo Electron Microscopy ◽  
Extreme Risk ◽  
Resolution Electron

The preparation of extremely thin samples, which are required for high-resolution electron microscopy, poses extreme risk of damaging biological macromolecules due to interactions with the air-water interface. Although the rapid increase in the number of published structures initially gave little indication that this was a problem, the search for methods that substantially mitigate this hazard is now intensifying. The two main approaches under investigation are ( a) immobilizating particles onto structure-friendly support films and ( b) reducing the length of time during which such interactions may occur. While there is little possibility of outrunning diffusion to the interface, intentional passivation of the interface may slow the process of adsorption and denaturation. In addition, growing attention is being given to gaining more effective control of the thickness of the sample prior to vitrification. Expected final online publication date for the Annual Review of Biochemistry, Volume 90 is June 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Cardiomyocyte Microtubules: Control of Mechanics, Transport, and Remodeling

2021 ◽  
Vol 84 (1) ◽  
Author(s):  
Keita Uchida ◽  
Emily A. Scarborough ◽  
Benjamin L. Prosser
Keyword(s):  
Posttranslational Modifications ◽  
Protein Translation ◽  
Calcium Handling ◽  
Annual Review ◽  
Publication Date ◽  
Microtubule Associated Proteins ◽  
New Concepts ◽  
Cardiomyocyte Contractility ◽  
Associated Proteins ◽  
Cytoskeletal Elements

Microtubules are essential cytoskeletal elements found in all eukaryotic cells. The structure and composition of microtubules regulate their function, and the dynamic remodeling of the network by posttranslational modifications and microtubule-associated proteins generates diverse populations of microtubules adapted for various contexts. In the cardiomyocyte, the microtubules must accommodate the unique challenges faced by a highly contractile, rigidly structured, and long-lasting cell. Through their canonical trafficking role and positioning of mRNA, proteins, and organelles, microtubules regulate essential cardiomyocyte functions such as electrical activity, calcium handling, protein translation, and growth. In a more specialized role, posttranslationally modified microtubules form load-bearing structures that regulate myocyte mechanics and mechanotransduction. Modified microtubules proliferate in cardiovascular diseases, creating stabilized resistive elements that impede cardiomyocyte contractility and contribute to contractile dysfunction. In this review, we highlight the most exciting new concepts emerging from recent studies into canonical and noncanonical roles of cardiomyocyte microtubules. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Quality Control of Procollagen in Cells

2021 ◽  
Vol 90 (1) ◽  
Author(s):  
Shinya Ito ◽  
Kazuhiro Nagata
Keyword(s):  
Quality Control ◽  
Posttranslational Modifications ◽  
Helical Structure ◽  
Basement Membranes ◽  
Annual Review ◽  
Publication Date ◽  
Normal Body Temperature ◽  
Current State ◽  
Triple Helical Structure

Collagen is the most abundant protein in mammals. A unique feature of collagen is its triple-helical structure formed by the Gly-Xaa-Yaa repeats. Three single chains of procollagen make a trimer, and the triple-helical structure is then folded in the endoplasmic reticulum (ER). This unique structure is essential for collagen's functions in vivo, including imparting bone strength, allowing signal transduction, and forming basement membranes. The triple-helical structure of procollagen is stabilized by posttranslational modifications and intermolecular interactions, but collagen is labile even at normal body temperature. Heat shock protein 47 (Hsp47) is a collagen-specific molecular chaperone residing in the ER that plays a pivotal role in collagen biosynthesis and quality control of procollagen in the ER. Mutations that affect the triple-helical structure or result in loss of Hsp47 activity cause the destabilization of procollagen, which is then degraded by autophagy. In this review, we present the current state of the field regarding quality control of procollagen. Expected final online publication date for the Annual Review of Biochemistry, Volume 90 is June 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Emerging Roles of Posttranslational Modifications in Plant-Pathogenic Fungi and Bacteria

2021 ◽  
Vol 59 (1) ◽  
Author(s):  
Wende Liu ◽  
Lindsay Triplett ◽  
Xiao-Lin Chen
Keyword(s):  
Posttranslational Modifications ◽  
Protein Function ◽  
Plant Pathogens ◽  
Pathogenic Fungi ◽  
Annual Review ◽  
Publication Date ◽  
Plant Pathogenic Fungi ◽  
Plant Interactions ◽  
Host Infection ◽  
Infection Processes

Posttranslational modifications (PTMs) play crucial roles in regulating protein function and thereby control many cellular processes and biological phenotypes in both eukaryotes and prokaryotes. Several recent studies illustrate how plant fungal and bacterial pathogens use these PTMs to facilitate development, stress response, and host infection. In this review, we discuss PTMs that have key roles in the biological and infection processes of plant-pathogenic fungi and bacteria. The emerging roles of PTMs during pathogen–plant interactions are highlighted. We also summarize traditional tools and emerging proteomics approaches for PTM research. These discoveries open new avenues for investigating the fundamental infection mechanisms of plant pathogens and the discovery of novel strategies for plant disease control. Expected final online publication date for the Annual Review of Phytopathology, Volume 59 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Adaptable and Multifunctional Ion-Conducting Aquaporins

2021 ◽  
Vol 72 (1) ◽  
Author(s):  
Stephen D. Tyerman ◽  
Samantha A. McGaughey ◽  
Jiaen Qiu ◽  
Andrea J. Yool ◽  
Caitlin S. Byrt
Keyword(s):  
Protein Interactions ◽  
Posttranslational Modifications ◽  
Plant Biology ◽  
Annual Review ◽  
Publication Date ◽  
Grand Challenge ◽  
Water Fluxes ◽  
Anion Channels ◽  
Water Permeation ◽  
Ion Conducting

Aquaporins function as water and neutral solute channels, signaling hubs, disease virulence factors, and metabolon components. We consider plant aquaporins that transport ions compared to some animal counterparts. These are candidates for important, as yet unidentified, cation and anion channels in plasma, tonoplast, and symbiotic membranes. For those individual isoforms that transport ions, water, and gases, the permeability spans 12 orders of magnitude. This requires tight regulation of selectivity via protein interactions and posttranslational modifications. A phosphorylation-dependent switch between ion and water permeation in AtPIP2;1 might be explained by coupling between the gates of the four monomer water channels and the central pore of the tetramer. We consider the potential for coupling between ion and water fluxes that could form the basis of an electroosmotic transducer. A grand challenge in understanding the roles of ion transporting aquaporins is their multifunctional modes that are dependent on location, stress, time, and development. Expected final online publication date for the Annual Review of Plant Biology, Volume 72 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Unfolding and refolding of a quinone oxidoreductase: α-crystallin, a molecular chaperone, assists its reactivation

2001 ◽  
Vol 359 (3) ◽  
pp. 547-556 ◽  
Author(s):  
Shradha GOENKA ◽  
Bakthisaran RAMAN ◽  
Tangirala RAMAKRISHNA ◽  
Ch. Mohan RAO
Keyword(s):  
Tertiary Structure ◽  
Small Heat Shock Protein ◽  
Active State ◽  
Eye Lens ◽  
Quinone Oxidoreductase ◽  
Denatured State ◽  
Αb Crystallin ◽  
Partially Unfolded ◽  
Vertebrate Eye ◽  
Denatured States

α-Crystallin, a member of the small heat-shock protein family and present in vertebrate eye lens, is known to prevent the aggregation of other proteins under conditions of stress. However, its role in the reactivation of enzymes from their non-native inactive states has not been clearly demonstrated. We have studied the effect of α-crystallin on the refolding of ∊-crystallin, a quinone oxidoreductase, from its different urea-denatured states. Co-refolding ∊-crystallin from its denatured state in 2.5M urea with either calf eye lens α-crystallin or recombinant human αB-crystallin could significantly enhance its reactivation yield. αB-crystallin was found to be more efficient than αA-crystallin in chaperoning the refolding of ∊-crystallin. In order to understand the nature of the denatured state(s) of ∊-crystallin that can interact with α-crystallin, we have investigated the unfolding pathway of ∊-crystallin. We find that it unfolds through three distinct intermediates: an altered tetramer, a partially unfolded dimer, which is competent to fold back to its active state, and a partially unfolded monomer. The partially unfolded monomer is inactive, exhibits highly exposed hydrophobic surfaces and has significant secondary structural elements with little or no tertiary structure. This intermediate does not refold into the active state without assistance. α-Crystallin provides the required assistance and improves the reactivation yield several-fold.

scholarly journals Structural and Functional Peculiarities of α-Crystallin

Biology ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 85
Author(s):  
Olga M. Selivanova ◽  
Oxana V. Galzitskaya
Keyword(s):  
Three Dimensional ◽  
Dimensional Structure ◽  
Eye Lens ◽  
Major Protein ◽  
High Concentration ◽  
Functional Studies ◽  
Αb Crystallin ◽  
Shock Proteins

α-Crystallin is the major protein of the eye lens and a member of the family of small heat-shock proteins. Its concentration in the human eye lens is extremely high (about 450 mg/mL). Three-dimensional structure of native α-crystallin is unknown. First of all, this is the result of the highly heterogeneous nature of α-crystallin, which hampers obtaining it in a crystalline form. The modeling based on the electron microscopy (EM) analysis of α-crystallin preparations shows that the main population of the α-crystallin polydisperse complex is represented by oligomeric particles of rounded, slightly ellipsoidal shape with the diameter of about 13.5 nm. These complexes have molecular mass of about 700 kDa. In our opinion, the heterogeneity of the α-crystallin complex makes it impossible to obtain a reliable 3D model. In the literature, there is evidence of an enhanced chaperone function of α-crystallin during its dissociation into smaller components. This may indirectly indicate that the formation of heterogeneous complexes is probably necessary to preserve α-crystallin in a state inactive before stressful conditions. Then, not only the heterogeneity of the α-crystallin complex is an evolutionary adaptation that protects α-crystallin from crystallization but also the enhancement of the function of α-crystallin during its dissociation is also an evolutionary acquisition. An analysis of the literature on the study of α-crystallin in vitro led us to the assumption that, of the two α-crystallin isoforms (αA- and αB-crystallins), it is αA-crystallin that plays the role of a special chaperone for αB-crystallin. In addition, our data on X-ray diffraction analysis of α-crystallin at the sample concentration of about 170–190 mg/mL allowed us to assume that, at a high concentration, the eye lens α-crystallin can be in a gel-like stage. Finally, we conclude that, since all the accumulated data on structural-functional studies of α-crystallin were carried out under conditions far from native, they cannot adequately reflect the features of the functioning of α-crystallin in vivo.

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