51
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Biswas A, Das KP. Zn2+ Enhances the Molecular Chaperone Function and Stability of α-Crystallin. Biochemistry 2007; 47:804-16. [DOI: 10.1021/bi7011965] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ashis Biswas
- Protein Chemistry Laboratory, Department of Chemistry, Bose Institute, 93/1 APC Road, Kolkata 700 009, India
| | - Kali P. Das
- Protein Chemistry Laboratory, Department of Chemistry, Bose Institute, 93/1 APC Road, Kolkata 700 009, India
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52
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Jobby MK, Sharma Y. Caulollins from Caulobacter crescentus, a Pair of Partially Unstructured Proteins of βγ-Crystallin Superfamily, Gain Structure upon Binding Calcium. Biochemistry 2007; 46:12298-307. [DOI: 10.1021/bi700843q] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Maroor K. Jobby
- Center for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Yogendra Sharma
- Center for Cellular and Molecular Biology, Hyderabad 500007, India
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53
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Jobby MK, Sharma Y. Calcium-binding to lens βB2- and βA3-crystallins suggests that all β-crystallins are calcium-binding proteins. FEBS J 2007; 274:4135-47. [PMID: 17651443 DOI: 10.1111/j.1742-4658.2007.05941.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Crystallins are the major proteins of a mammalian eye lens. The topologically similar eye lens proteins, beta- and gamma-crystallins, are the prototype and founding members of the betagamma-crystallin superfamily. Betagamma-crystallins have until recently been regarded as structural proteins. However, the calcium-binding properties of a few members and the potential role of betagamma-crystallins in fertility are being investigated. Because the calcium-binding elements of other member proteins, such as spherulin 3a, are not present in betaB2-crystallin and other betagamma-crystallins from fish and mammalian genomes, it was argued that lens betagamma-crystallins should not bind calcium. In order to probe whether beta-crystallins can bind calcium, we selected one basic (betaB2) and one acidic (betaA3) beta-crystallin for calcium-binding studies. Using calcium-binding assays such as 45Ca overlay, terbium binding, Stains-All and isothermal titration calorimetry, we established that both betaB2- and betaA3-crystallin bind calcium with moderate affinity. There was no significant change in their conformation upon binding calcium as monitored by fluorescence and circular dichroism spectroscopy. However, 15N-1H heteronuclear single quantum correlation NMR spectroscopy revealed that amide environment of several residues underwent changes indicating calcium ligation. With the corroboration of calcium-binding to betaB2- and betaA3-crystallins, we suggest that all beta-crystallins bind calcium. Our results have important implications for understanding the calcium-related cataractogenesis and maintenance of ionic homeostasis in the lens.
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Affiliation(s)
- Maroor K Jobby
- Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India
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54
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Hao J, Narayanan K, Muni T, Ramachandran A, George A. Dentin Matrix Protein 4, a Novel Secretory Calcium-binding Protein That Modulates Odontoblast Differentiation. J Biol Chem 2007; 282:15357-65. [PMID: 17369251 DOI: 10.1074/jbc.m701547200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Formation of calcified tissues is a well regulated process. In dentin, the odontoblasts synthesize several biomolecules that function as nucleators or inhibitors of mineralization. To identify genes that are odontoblast-specific, a subtractive hybridization technique was employed that resulted in the identification of a previously undescribed novel gene synthesized by the odontoblasts. Based on the nomenclature in our laboratory, this gene has been named dentin matrix protein 4 (DMP4). The protein encoded by mouse DMP4 cDNA contained 579 amino acids, including a 26-amino acid signal peptide. Analysis of the protein sequence demonstrated the presence of a Greek key calcium-binding domain and one conserved domain of unknown function in all the species examined thus far. Calcium binding property was confirmed by (45)Ca binding assays and the corresponding change in conformation by far-ultraviolet circular dichroism. Northern analysis demonstrated high expression levels of a single 3-kb mRNA transcript in tooth, whereas low expression levels were detected in other tissues. In situ hybridization analysis showed high expression levels of DMP4 in odontoblasts and low levels in osteoblasts and ameloblasts during tooth development. Gain and loss of function experiments demonstrated that DMP4 had the potential to differentiate mesenchymal precursor cells into functional odontoblast-like cells.
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Affiliation(s)
- Jianjun Hao
- Department of Oral Biology, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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55
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Milam SL, Nicely NI, Feeney B, Mattos C, Clark AC. Rapid folding and unfolding of Apaf-1 CARD. J Mol Biol 2007; 369:290-304. [PMID: 17408690 PMCID: PMC2020445 DOI: 10.1016/j.jmb.2007.02.105] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2006] [Revised: 02/20/2007] [Accepted: 02/23/2007] [Indexed: 11/20/2022]
Abstract
Caspase recruitment domains (CARDs) are members of the death domain superfamily and contain six antiparallel helices in an alpha-helical Greek key topology. We have examined the equilibrium and kinetic folding of the CARD of Apaf-1 (apoptotic protease activating factor 1), which consists of 97 amino acid residues, at pH 6 and pH 8. The results showed that an apparent two state equilibrium mechanism is not adequate to describe the folding of Apaf-1 CARD at either pH, suggesting the presence of intermediates in equilibrium unfolding. Interestingly, the results showed that the secondary structure is less stable than the tertiary structure, based on the transition mid-points for unfolding. Single mixing and sequential mixing stopped-flow studies showed that Apaf-1 CARD folds and unfolds rapidly and suggest a folding mechanism that contains parallel channels with two unfolded conformations folding to the native conformation. Kinetic simulations show that a slow folding phase is described by a third conformation in the unfolded ensemble that interconverts with one or both unfolded species. Overall, the native ensemble is formed rapidly upon refolding. This is in contrast to other CARDs in which folding appears to be dominated by formation of kinetic traps.
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Affiliation(s)
- Sara L Milam
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, NC 27695, USA
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56
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Aravind P, Rajini B, Sharma Y, Sankaranarayanan R. Crystallization and preliminary X-ray crystallographic investigations on a betagamma-crystallin domain of absent in melanoma 1 (AIM1), a protein from Homo sapiens. Acta Crystallogr Sect F Struct Biol Cryst Commun 2006; 62:282-4. [PMID: 16511323 PMCID: PMC2197174 DOI: 10.1107/s1744309106005380] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Accepted: 02/15/2006] [Indexed: 11/10/2022]
Abstract
AIM1g1 is a single betagamma-crystallin domain from the protein absent in melanoma 1 (AIM1), which appears to play a role in the suppression of melanomas. This domain is known to bind calcium and its structure would help in identifying calcium-coordinating sites in vertebrate crystallins, which have hitherto been believed to have lost this ability during evolution. Crystallization of this domain was performed by the hanging-drop vapour-diffusion method. Crystals diffracted to a maximum resolution of 1.86 A and were found to belong to space group P6(1) or P6(5), with unit-cell parameters a = b = 54.98, c = 59.73 A. Solvent-content analysis indicated the presence of one monomer per asymmetric unit.
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Affiliation(s)
- Penmatsa Aravind
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
| | - Bheemreddy Rajini
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
| | - Yogendra Sharma
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
| | - Rajan Sankaranarayanan
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
- Correspondence e-mail:
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57
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Hao J, He G, Narayanan K, Zou B, Lin L, Muni T, Ramachandran A, George A. Identification of differentially expressed cDNA transcripts from a rat odontoblast cell line. Bone 2005; 37:578-88. [PMID: 16054450 DOI: 10.1016/j.bone.2005.05.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2004] [Revised: 04/08/2005] [Accepted: 05/13/2005] [Indexed: 10/25/2022]
Abstract
Odontoblasts and osteoblasts are two among the myriads of cell types present in the craniofacial complex. Both have a common ectomesenchymal origin and secrete macromolecules that are necessary for the formation of dentin and alveolar bone via matrix-mediated mechanisms. The mineralized matrices of bone and dentin differ in morphology and function but several mineral associated proteins, formerly thought to be tissue specific, have been found to be common in both tissues. To decipher the complex molecular mechanisms involved in mineralized dentin formation, the suppressive subtraction hybridization (SSH) approach has been used to identify the genes expressed by polarized odontoblasts. Employing SSH, 187 cDNA clones were identified from the subtracted cDNA library. Many of these genes have not been previously reported to be expressed by terminally differentiated odontoblasts. Genes were classified into seven groups based on the predicted function of the encoded proteins: extracellular matrix; cytoskeletal components, molecules involved in adhesion and cell-cell interaction; metabolic enzymes, transporters, ion channels; protein processing, protein transport and protein folding molecules; nuclear proteins (transcription factors, DNA processing enzymes); signaling molecules and genes of yet unknown function. Northern blot and in situ hybridization analysis performed for five putative novel genes and one new isoform of amelogenin revealed differential expression levels in the osteoblasts, ameloblasts and the odontoblasts of the developing rat molars. Some of the known genes isolated from this enriched pool were the cleavage products of dentin sialophosphoprotein (DSPP) namely, phosphophoryn (PP) and dentin sialoprotein (DSP). Interestingly amelogenin, ameloblastin and enamelin were also expressed in the odontoblasts during dentin formation.
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Affiliation(s)
- Jianjun Hao
- Department of Oral Biology (M/C 690), University of Illinois at Chicago, Chicago, IL 60612, USA
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58
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Marian MJ, Li H, Borchman D, Paterson CA. Plasma membrane Ca2+-ATPase expression in the human lens. Exp Eye Res 2005; 81:57-64. [PMID: 15978255 DOI: 10.1016/j.exer.2005.01.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2004] [Revised: 12/22/2004] [Accepted: 01/14/2005] [Indexed: 10/25/2022]
Abstract
The focus of the study was to characterize plasma membrane calcium-ATPase pump (PMCA) isoform expression in the human lens and cultured lens epithelial cells as a basis for future studies of calcium homeostasis in the lens. Proteins and mRNA expression were analysed using Western Immunoblotting and reverse transcription polymerase chain reaction (RT-PCR), respectively. Clear human lenses from the Kentucky Lions Eye Bank and an immortalized human lens epithelial cell line (HLE B-3) were used. RT-PCR products of PMCA1, PMCA2, and PMCA4 primers were detected at 429, 557, and 849bp, respectively. All these products were identified as PMCA isoforms by sequence analysis. Protein bands at approximately 130, 115, and 135kDa were detected by Western blot analysis for PMCA1, PMCA2 and PMCA4, respectively. PMCA3 was not detected at protein or mRNA level in any human lens sample or cell culture, but was detected in the rat brain cortex used as a control. Several bands with lower molecular weights, especially for PMCA2, were detected in the epithelial samples and probably represent break down products of PMCA2. No PMCA proteins or breakdown products were detected in the nuclear or cortical fractions from human lenses. PMCA1, 2, and 4 proteins and mRNAs are expressed in human lens epithelium and cultured epithelial cells; PMCA3 is not. PMCA was not detected at all in the lens fibre cells. The calcium pump must be selectively processed, independent of other membrane proteins such as the Na-K-ATPase pumps, because the distribution of the Na-K-ATPase pump is asymmetrical in the epithelium and present throughout the lens whereas the calcium pumps are not. The findings of this study provide a basis for further studies to examine the role and modulation of PMCA isoforms in calcium homeostasis and in the development of cataract.
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Affiliation(s)
- M J Marian
- Department of Biochemistry and Molecular Biology, University of Louisville, 301 E. Muhammad Ali Blvd., Louisville, KY 40202, USA
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59
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Giancola C, Pizzo E, Di Maro A, Cubellis MV, D'Alessio G. Preparation and characterization of geodin. A betagamma-crystallin-type protein from a sponge. FEBS J 2005; 272:1023-35. [PMID: 15691335 DOI: 10.1111/j.1742-4658.2004.04536.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Geodin is a protein encoded by a sponge gene homologous to genes from the betagamma-crystallins superfamily. The interest for this crystallin-type protein stems from the phylogenesis of porifera, commonly called sponges, the earliest divergence event in the history of metazoans. Here we report the preparation of geodin as a recombinant protein from Escherichia coli, its characterization through physico-chemical analyses, and a model of its 3D structure based on homology modelling. Geodin is a monomeric protein of about 18 kDa, with an all-beta structure, as all other crystallins in the superfamily, but more prone to unfold in the presence of chemical denaturants, when compared with other homologues from the superfamily. Its thermal unfolding, studied by far- and near-CD, and by calorimetry, is described by a two-state model. Geodin appears to be structurally similar in many respects to the bacterial protein S crystallin, with which it also shares a significant, albeit more modest stabilizing effect exerted by calcium ions. These results suggest that the crystallin-type structural scaffold, employed in the evolution of bacteria and moulds, was successfully recruited very early in the evolution of metazoa.
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60
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Bhat SP. Transparency and non-refractive functions of crystallins--a proposal. Exp Eye Res 2005; 79:809-16. [PMID: 15642317 DOI: 10.1016/j.exer.2004.08.020] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Accepted: 08/18/2004] [Indexed: 11/26/2022]
Abstract
Based on the premise that all crystallins have cellular and metabolically relevant catalytic activities, we propose that aberrant changes in non-crystallin (non-refractive) functions presage the appearance of cataractous pathologies in an otherwise highly stable edifice of transparency. This proposal is based on accumulating evidence from developmental, molecular and genetic studies that have established that crystallins are more than inanimate building blocks of the transparent lens fiber mass. The published work does not support the perceived dichotomy in the relevance of crystallin function (as essential) and non-crystallin function (as either of secondary importance or not essential at all), to the emergence and maintenance of the phenotype of transparency. A number of crystallin mutations have stage-specific phenotypes at developmental times when their concentrations have not reached 'crystallin' (high) proportions. There is heterogeneity in the cataract phenotypes associated with similar or identical mutations in different populations; the cataracts have disparate phenotypes even when the mutations are in the same gene. These data suggest that non-crystallin function is not merely a non-lens activity of a crystallin but an essential requirement within the lens itself.
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Affiliation(s)
- Suraj P Bhat
- Jules Stein Eye Institute, Brain Research Institute, Geffen School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095-7000, USA.
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61
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Abstract
Betagamma-crystallin is a superfamily with diverse members from vertebrate lens to microbes. However, not many members have been identified and studied. Here, we report the identification of a putative exported protein from Yersinia pestis as a member of the betagamma-crystallin superfamily. Even though calcium has been known to play an important role in the physiology and virulence of the Yersinia genus, calcium-binding proteins have not yet been identified. We have studied the calcium-binding properties of two of the three crystallin domains present in this putative exported protein designated "Yersinia crystallin." These two domains (D1 and D2) have unique AA and BB types of arrangement of their Greek key motifs unlike the domains of other members of the betagamma-crystallin superfamily, which are either AB or BA types. These domains bind two calcium ions with low and high affinity-binding sites. We showed their calcium-binding properties using various probes for calcium and the effect of calcium on their secondary and tertiary structures. Although both domains bind calcium, D1 underwent drastic changes in secondary and tertiary structure and hydrodynamic volume upon calcium binding. Domain D1, which is intrinsically unstructured in the apo form, requires calcium for the typical betagamma-crystallin fold. Calcium exerted an extrinsic stabilization effect on domain D1 but not on D2, which is also largely unstructured. We suggest that this protein might be involved in calcium-dependent processes, such as stress response or physiology in the Yersinia genus, similar to its microbial relatives and mammalian lens crystallins.
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Affiliation(s)
- Maroor K Jobby
- Center for Cellular and Molecular Biology, Uppal Road, Hyderabad-500007, India
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62
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Bao L, Kaldany C, Holmstrand EC, Cox DH. Mapping the BKCa channel's "Ca2+ bowl": side-chains essential for Ca2+ sensing. ACTA ACUST UNITED AC 2004; 123:475-89. [PMID: 15111643 PMCID: PMC2234491 DOI: 10.1085/jgp.200409052] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
There is controversy over whether Ca2+ binds to the BKCa channel's intracellular domain or its integral-membrane domain and over whether or not mutations that reduce the channel's Ca2+ sensitivity act at the point of Ca2+ coordination. One region in the intracellular domain that has been implicated in Ca2+ sensing is the “Ca2+ bowl”. This region contains many acidic residues, and large Ca2+-bowl mutations eliminate Ca2+ sensing through what appears to be one type of high-affinity Ca2+-binding site. Here, through site-directed mutagenesis we have mapped the residues in the Ca2+ bowl that are most important for Ca2+ sensing. We find acidic residues, D898 and D900, to be essential, and we find them essential as well for Ca2+ binding to a fusion protein that contains a portion of the BKCa channel's intracellular domain. Thus, much of our data supports the conclusion that Ca2+ binds to the BKCa channel's intracellular domain, and they define the Ca2+ bowl's essential Ca2+-sensing motif. Overall, however, we have found that the relationship between mutations that disrupt Ca2+ sensing and those that disrupt Ca2+ binding is not as strong as we had expected, a result that raises the possibility that, when examined by gel-overlay, the Ca2+ bowl may be in a nonnative conformation.
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Affiliation(s)
- Lin Bao
- Molecular Cardiology Research Institute, New England Medical Center, Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
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63
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Bloemendal H, de Jong W, Jaenicke R, Lubsen NH, Slingsby C, Tardieu A. Ageing and vision: structure, stability and function of lens crystallins. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2004; 86:407-85. [PMID: 15302206 DOI: 10.1016/j.pbiomolbio.2003.11.012] [Citation(s) in RCA: 633] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The alpha-, beta- and gamma-crystallins are the major protein components of the vertebrate eye lens, alpha-crystallin as a molecular chaperone as well as a structural protein, beta- and gamma-crystallins as structural proteins. For the lens to be able to retain life-long transparency in the absence of protein turnover, the crystallins must meet not only the requirement of solubility associated with high cellular concentration but that of longevity as well. For proteins, longevity is commonly assumed to be correlated with long-term retention of native structure, which in turn can be due to inherent thermodynamic stability, efficient capture and refolding of non-native protein by chaperones, or a combination of both. Understanding how the specific interactions that confer intrinsic stability of the protein fold are combined with the stabilizing effect of protein assembly, and how the non-specific interactions and associations of the assemblies enable the generation of highly concentrated solutions, is thus of importance to understand the loss of transparency of the lens with age. Post-translational modification can have a major effect on protein stability but an emerging theme of the few studies of the effect of post-translational modification of the crystallins is one of solubility and assembly. Here we review the structure, assembly, interactions, stability and post-translational modifications of the crystallins, not only in isolation but also as part of a multi-component system. The available data are discussed in the context of the establishment, the maintenance and finally, with age, the loss of transparency of the lens. Understanding the structural basis of protein stability and interactions in the healthy eye lens is the route to solve the enormous medical and economical problem of cataract.
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Affiliation(s)
- Hans Bloemendal
- Department of Biochemistry, University of Nijmegen, 6500HB, The Netherlands
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64
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Lee CH, Jung JW, Yee A, Arrowsmith CH, Lee W. Solution structure of a novel calcium binding protein, MTH1880, from Methanobacterium thermoautotrophicum. Protein Sci 2004; 13:1148-54. [PMID: 15044740 PMCID: PMC2280053 DOI: 10.1110/ps.03472104] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
MTH1880 is a hypothetical protein from Methanobacterium thermoautotrophicum, a target organism of structural genomics. The solution structure determined by NMR spectroscopy demonstrates a typical alpha + beta-fold found in many proteins with different functions. The molecular surface of the protein reveals a small, highly acidic pocket comprising loop B (Asp36, Asp37, Asp38), the end of beta2 (Glu39), and loop D (Ser57, Ser58, Ser61), indicating that the protein would have a possible cation binding site. The NMR resonances of several amino acids within the acidic binding pocket in MTH1880, shifted upon addition of calcium ion. This calcium binding motif and overall topology of MTH1880 differ from those of other calcium binding proteins. MTH1880 did not show a calcium-induced conformational change typical of calcium sensor proteins. Therefore, we propose that the MTH1880 protein contains a novel motif for calcium-specific binding, and may function as a calcium buffering protein.
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Affiliation(s)
- Chang-Hun Lee
- Department of Biochemistry, College of Science, Yonsei University, 134 Seodaemoon-Gu, Shinchondong, Seoul, Korea 120-749
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65
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Vrensen GFJM, van Marle J, Jonges R, Voorhout W, Breipohl W, Wegener AR. Tryptophan deficiency arrests chromatin breakdown in secondary lens fibers of rats. Exp Eye Res 2004; 78:661-72. [PMID: 15106946 DOI: 10.1016/j.exer.2003.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Tryptophan deficiency is known for long time to cause cataract in rats. However, up till now the underlying mechanism is still enigmatic. Histological studies showed an extended lens bow suggesting that the normal breakdown of nuclei in the lens fibres is arrested under these conditions. Using advanced ultrastructural techniques we aimed to clarify this aberrant final differentiation of lens fibres. Albino and pigmented rats were permanently or intermittently raised on a tryptophan deficient diet for 12 and 16 weeks, respectively. Rats of the same age raised on a normal diet served as controls. Lenses were treated for light and electron microscopy. For histology sections were stained for DNA and gamma-crystallins. In addition to routine transmission electron microscopy (TEM), ultrathin sections were subjected to electron tomography and energy dispersive X-ray microanalysis (EDX). Histology verified the extended lens bow for albino and pigmented rats and showed that in the intermittent period of normal diet the fibre nuclei are broken down as in controls. It was further shown that gamma-crystallins are co-localized with DNA in the nuclear domain. TEM revealed that during final differentiation nuclear chromatin becomes highly compacted in a chromosome-like manner and than rapidly evanesces in control rats. This compacted stage persists indefinitely in the tryptophan deficient rats. Electron tomography showed that during differentiation chromatin is first uncoiled to 30 nm solenoids, subsequently to highly compacted 10 nm beads-on-a-string fibrils and than is segregated from the nuclear proteins. EDX revealed that the late stage persisting nuclei consist of domains rich in DNA associated with histones and in domains with mainly proteins. This study corroborates previous findings on the final breakdown of nuclei of lens fibres. It further shows that the chromatin is ultimately uncoiled to beads-on-a-string fibrils and that as the last step chromatin is broken down at this unmasked stage. Except for this last step nuclear breakdown is identical in control and tryptophan deficient rats suggesting that it is not the availability of tryptophan for protein synthesis in general which causes the arrest. Two alternatives for this final arrest are discussed. A low tryptophan content, most pronounced in deeper cortical layers, may inhibit the late synthesis of the DNases and proteases necessary for chromatin breakdown. The radical scavenging by indoleamine 2,3-dioxygenase, which cleaves the pyrrole ring of tryptophan to form formylkynurenine using free oxygen radicals, is impaired by low levels of tryptophan. This decreased scavenging of oxygen radicals will expose the catalytic enzymes for chromatin breakdown, residing in the nucleus in an inactive form for quite a long period, to high levels of oxygen radicals and may affect the activity of these enzymes and therefore the execution of the chromatin breakdown.
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Affiliation(s)
- Gijs F J M Vrensen
- Department of Ophthalmology, Leiden University Medical Centre, Leiden, The Netherlands.
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66
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Li D, Sun F, Wang K. Protein profile of aging and its retardation by caloric restriction in neural retina. Biochem Biophys Res Commun 2004; 318:253-8. [PMID: 15110781 DOI: 10.1016/j.bbrc.2004.04.022] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2004] [Indexed: 11/19/2022]
Abstract
Aging is a slow, gradual deterioration process of an organism. The only experimental intervention, which can reliably retard aging and age-related degenerative diseases, is dietary caloric restriction (CR). To gain insight into the mechanism of CR intervention, we have investigated the protein profile of aging and its retardation by CR in the neural retina of Brown Norway (BN) rats using the comprehensive proteomic approach. We found that the intensities of 18 proteins decreased significantly with age. CR intervention can completely prevent seven of them, and partially protect eight of them, from such age-related declines. The major protein targets protected by CR intervention appear to be glycolytic enzymes and molecular chaperones. These data are the first to suggest that CR may retard the age-related degeneration of retina by maintaining sufficient glucose metabolism, by ensuring proper protein folding, and/or by preventing protein denaturation in the neural retina.
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Affiliation(s)
- Dayu Li
- Department of Ophthalmology, College of Physicians and Surgeons of Columbia University, New York, NY, USA
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67
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Chen YR, Clark AC. Equilibrium and kinetic folding of an alpha-helical Greek key protein domain: caspase recruitment domain (CARD) of RICK. Biochemistry 2003; 42:6310-20. [PMID: 12755636 DOI: 10.1021/bi0340752] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have characterized the equilibrium and kinetic folding of a unique protein domain, caspase recruitment domain (CARD), of the RIP-like interacting CLARP kinase (RICK) (RICK-CARD), which adopts a alpha-helical Greek key fold. At equilibrium, the folding of RICK-CARD is well described by a two-state mechanism representing the native and unfolded ensembles. The protein is marginally stable, with a DeltaG(H)()2(O) of 3.0 +/- 0.15 kcal/mol and an m-value of 1.27 +/- 0.06 kcal mol(-1) M(-1) (30 mM Tris-HCl, pH 8, 1 mM DTT, 25 degrees C). While the m-value is constant, the protein stability decreases in the presence of moderate salt concentrations (below 200 mM) and then increases at higher salt concentrations. The results suggest that electrostatic interactions are stabilizing in the native protein, and the favorable Coulombic interactions are reduced at low ionic strength. Above 200 mM salt, the results are consistent with Hofmeister effects. The unfolding pathway of RICK-CARD is complex and contains at least three non-native conformations. The refolding pathway of RICK-CARD also is complex, and the data suggest that the unfolded protein folds via two intermediate conformations prior to reaching the native state. Overall, the data suggest the presence of kinetically trapped, or misfolded, species that are on-pathway both in refolding and in unfolding.
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Affiliation(s)
- Yun-Ru Chen
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh 27695, USA
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68
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Rajini B, Graham C, Wistow G, Sharma Y. Stability, homodimerization, and calcium-binding properties of a single, variant betagamma-crystallin domain of the protein absent in melanoma 1 (AIM1). Biochemistry 2003; 42:4552-9. [PMID: 12693952 DOI: 10.1021/bi027384l] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIM1 (absent in melanoma), a candidate suppressor of malignancy in melanoma, is a nonlens member of the betagamma-crystallin superfamily, which contains six predicted betagamma domains. The first betagamma-crystallin domain of AIM1 (AIM1-g1) diverges most in sequence from the superfamily consensus. To examine its ability to fold and behave like a normal betagamma domain, we cloned AIM1-g1 and overexpressed it in Escherichia coli as a recombinant protein. The recombinant domain was found to be a stable, soluble protein, similar to lens protein gammaBeta-crystallin in secondary structure. The tertiary structure of AIM1-g1 is dominated by the contribution of aromatic amino acids and cysteine. AIM1-g1 undergoes concentration-independent, noncovalent homodimerization with no trace of monomer, similar to a one-domain protein spherulin 3a. Since many betagamma domain proteins bind calcium, we have also investigated the calcium-binding properties of AIM1-g1 by various methods. AIM1-g1 binds the calcium-mimic dye Stains-all, the calcium probe terbium (with K(D) 170 microM), and (45)Ca when blotted on a membrane. AIM1-g1 binds calcium (K(D) 30 microM) with a comparatively higher affinity than bovine lens gamma-crystallin (90 microM). However, calcium binding does not induce significant change in the protein conformation in the near- and far-UV CD and in fluorescence. The AIM1-g1 domain is as stable as domains of betagamma-crystallins (betaB2- or gammaS-crystallins) as monitored by guanidinium chloride unfolding (midpoint of unfolding transition is 1.8 M GdmCl), and the stability of the protein is not altered upon binding calcium as evaluated by equilibrium unfolding. These results show that, despite the sequence variation, AIM1-g1 folds such as a betagamma domain, binds calcium and undergoes dimerization.
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Affiliation(s)
- Bheemreddy Rajini
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad-500007, India
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69
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del Valle LJ, Escribano C, Pérez JJ, Garriga P. Calcium-induced decrease of the thermal stability and chaperone activity of alpha-crystallin. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1601:100-9. [PMID: 12429508 DOI: 10.1016/s1570-9639(02)00429-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Alpha-crystallin, one of the major proteins in the vertebrate eye lens, acts as a molecular chaperone, like the small heat-shock proteins, by protecting other proteins from denaturing under stress or high temperature conditions. alpha-Crystallin aggregation is involved in lens opacification, and high [Ca(2+)] has been associated with cataract formation, suggesting a role for this cation in the pathological process. We have investigated the effect of Ca(2+) on the thermal stability of alpha-crystallin by UV and Fourier-transform infrared (FTIR) spectroscopies. In both cases, a Ca(2+)-induced decrease in the midpoint of the thermal transition is detected. The presence of high [Ca(2+)] results also in a marked decrease of its chaperone activity in an insulin-aggregation assay. Furthermore, high Ca(2+) concentration decreases Cys reactivity towards a sulfhydryl reagent. The results obtained from the spectroscopic analysis, and confirmed by circular dichroism (CD) measurements, indicate that Ca(2+) decreases both secondary and tertiary-quaternary structure stability of alpha-crystallin. This process is accompanied by partial unfolding of the protein and a clear decrease in its chaperone activity. It is concluded that Ca(2+) alters the structural stability of alpha-crystallin, resulting in impaired chaperone function and a lower protective ability towards other lens proteins. Thus, alpha-crystallin aggregation facilitated by Ca(2+) would play a role in the progressive loss of transparency of the eye lens in the cataractogenic process.
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Affiliation(s)
- Luis J del Valle
- Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Colom 1, 08222 Terrassa, Catalonia, Spain
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70
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Wilkins AL, Ye Y, Yang W, Lee HW, Liu ZR, Yang JJ. Metal-binding studies for a de novo designed calcium-binding protein. Protein Eng Des Sel 2002; 15:571-4. [PMID: 12200539 DOI: 10.1093/protein/15.7.571] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
To understand the key determinants in calcium-binding affinity, a calcium-binding site with pentagonal bipyramid geometry was designed into a non-calcium-binding protein, domain 1 of CD2. This metal-binding protein has five mutations with a net charge in the coordination sphere of -5 and is termed DEEEE. Fluorescence resonance energy transfer was used to determine the metal-binding affinity of DEEEE to the calcium analog terbium. The addition of protein concentration to Tb(III) solution results in a large enhancement of Tb(III) fluorescence due to energy transfer between terbium ions and aromatic residues in CD2-D1. In addition, both calcium and lanthanum compete with terbium for the same desired metal binding pocket. Our designed protein exhibits a stronger affinity for Tb(III), with a K(d) of 21 microM, than natural calcium-binding proteins with a similar Greek key scaffold.
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Affiliation(s)
- Anna L Wilkins
- Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
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