Small heat shock proteins and α-crystallins: Dynamic proteins with flexible functions

Department of Chemistry & Biochemistry, 1007 E. Lowell Street, University of Arizona, Tucson, AZ 85743, USA.
Trends in Biochemical Sciences (Impact Factor: 11.23). 12/2011; 37(3):106-17. DOI: 10.1016/j.tibs.2011.11.005
Source: PubMed


The small heat shock proteins (sHSPs) and the related α-crystallins (αCs) are virtually ubiquitous proteins that are strongly induced by a variety of stresses, but that also function constitutively in multiple cell types in many organisms. Extensive research has demonstrated that a majority of sHSPs and αCs can act as ATP-independent molecular chaperones by binding denaturing proteins and thereby protecting cells from damage due to irreversible protein aggregation. As a result of their diverse evolutionary history, their connection to inherited human diseases, and their novel protein dynamics, sHSPs and αCs are of significant interest to many areas of biology and biochemistry. However, it is increasingly clear that no single model is sufficient to describe the structure, function or mechanism of action of sHSPs and αCs. In this review, we discuss recent data that provide insight into the variety of structures of these proteins, their dynamic behavior, how they recognize substrates, and their many possible cellular roles.

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Available from: Elizabeth Vierling, Feb 04, 2014
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    • "sHSPs that have low molecular weights (usually less than 30 kDa) and contain a conserved α-crystallin domain (ACD; 80-100 AA), are ancient, ubiquitous, and diverse in living organisms. sHSPs usually form oligomers ranging from 9 to 50 subunits (200-800 kDa) (Basha et al., 2012; Lopes-Caitar et al., 2013). The ACD is located in the C-terminal region. "
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    ABSTRACT: Small heat shock proteins (sHSPs) are essential for the plant’s normal development and stress responses, especially the heat stress response. The information regarding sHSP genes in Chinese cabbage (Brassica rapa ssp pekinensis) is sparse, hence we performed a genome-wide analysis to identify sHSP genes in this species. We identified 26 non-redundant sHSP genes distributed on all chromosomes, except chromosome A7, with one additional sHSP gene identified from an expressed sequence tag library. Chinese cabbage was found to contain more sHSP genes than Arabidopsis. The 27 sHSP genes were classified into 11 subfamilies. We identified 22 groups of sHSP syntenic orthologous genes between Chinese cabbage and Arabidopsis. In addition, eight groups of paralogous genes were uncovered in Chinese cabbage. Protein structures of the 27 Chinese cabbage sHSPs were modeled using Phyre2, which revealed that all of them contain several conserved β strands across different subfamilies. In general, gene structure was conserved within each subfamily between Chinese cabbage and Arabidopsis, except for peroxisome sHSP. Analysis of promoter motifs showed that most sHSP genes contain heat shock elements or variants. We also found that biased gene loss has occurred during the evolution of the sHSP subfamily in Chinese cabbage. Expression analysis indicated that the greatest transcript abundance of most Chinese cabbage sHSP genes was found in siliques and early cotyledon embryos. Thus, genome-wide identification and characterization of sHSP genes is a first and important step in the investigation of sHSPs in Chinese cabbage.
    Preview · Article · Oct 2015 · Genetics and molecular research: GMR
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    • " oligomeric complex , is dodecameric in nature and function as a molecular chaperone ( Figure 3 ) . Studies on wheat sHSP16 . 9 also demonstrated a dodecameric structure of this heat shock protein although homologs from other species have been shown to have structures with subunits ranging between 2 and >48 subunits ( van Montfort et al . , 2001 ; Basha et al . , 2012 ) . This is well known that sHSPs function in plant stress adaptation by binding to vulnerable cellular proteins during stress conditions , prevent their aggregation and thus hold them in a competent state for refolding by other chaperones ( Ehrnsperger et al . , 1997 ; Veinger et al . , 1998 ; Murakami et al . , 2004 ) . Our data clear"
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    ABSTRACT: Small heat shock proteins (sHSPs) are a diverse group of proteins and are highly abundant in plant species. Although majority of these sHSPs were shown to express specifically in seed, their potential function in seed physiology remains to be fully explored. Our proteomic analysis revealed that OsHSP18.2, a class II cytosolic HSP is an aging responsive protein as its abundance significantly increased after artificial aging in rice seeds. OsHSP18.2 transcript was found to markedly increase at the late maturation stage being highly abundant in dry seeds and sharply decreased after germination. Our biochemical study clearly demonstrated that OsHSP18.2 forms homooligomeric complex and is dodecameric in nature and functions as a molecular chaperone. OsHSP18.2 displayed chaperone activity as it was effective in preventing thermal inactivation of Citrate Synthase. Further, to analyze the function of this protein in seed physiology, seed specific Arabidopsis overexpression lines for OsHSP18.2 were generated. Our subsequent functional analysis clearly demonstrated that OsHSP18.2 has ability to improve seed vigor and longevity by reducing deleterious ROS accumulation in seeds. In addition, transformed Arabidopsis seeds also displayed better performance in germination and cotyledon emergence under adverse conditions. Collectively, our work demonstrates that OsHSP18.2 is an aging responsive protein which functions as a molecular chaperone and possibly protect and stabilize the cellular proteins from irreversible damage particularly during maturation drying, desiccation and aging in seeds by restricting ROS accumulation and thereby improves seed vigor, longevity and seedling establishment.
    Full-text · Article · Sep 2015 · Frontiers in Plant Science
    • "Nonetheless, eye lens proteins undergo covalent and noncovalent modifications throughout the life-span and become increasingly prone to unfolding and aggregation. As members of the small heat-shock protein (sHsp) family [10] [11] [12], α-crystallins are believed to protect the eye lens from the severe consequences of irreversible protein aggregation by effectively binding non-native proteins [13] [14]. "
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    ABSTRACT: The two α-crystallins (αA- and αB-crystallin) are major components of our eye lenses. Their key function there is to preserve lens transparency which is a challenging task as the protein turnover in the lens is low necessitating the stability and longevity of the constituent proteins. α-crystallins are members of the small heat shock protein family. αB-crystallin is also expressed in other cell types. The review summarizes the current concepts on the polydisperse structure of the α-crystallin oligomer and its chaperone function with a focus on the inherent complexity and highlighting gaps between in vitro and in vivo studies. Both α-crystallins protect proteins from irreversible aggregation in a promiscuous manner. In maintaining eye lens transparency, they reduce the formation of light scattering particles and balance the interactions between lens crystallins. Important for these functions is their structural dynamics and heterogeneity as well as the regulation of these processes which we are beginning to understand. However, currently, it still remains elusive to which extent the in vitro observed properties of α-crystallins reflect the highly crowded situation in the lens. Since α-crystallins play an important role in preventing cataract in the eye lens and in the development of diverse diseases, understanding their mechanism and substrate spectra is of importance. To bridge the gap between the concepts established in vitro and the in vivo function of α-crystallins, the joining of forces between different scientific disciplines and the combination of diverse techniques in hybrid approaches are necessary. Copyright © 2015. Published by Elsevier B.V.
    No preview · Article · Jun 2015 · Biochimica et Biophysica Acta
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