Analysis of crystallin-crystallin interactions by surface plasmon resonance

Surface plasmon resonance study of the interaction of 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid dipotassium salt (bis-ANS) and adenosine triphosphate (ATP) with oligomeric recombinant human lens αA-crystallin

α-Crystallin, an abundant mammalian lens protein made up of two subunits (αA- and αB-crystallin), is involved in the maintenance of the optimal refractive index in the lens. The protein is implicated in the pathophysiology of a large number of retinal diseases including cataract, age-related macular degeneration, diabetic retinopathy, and uveitis. α-Crystallin belongs to the small heat shock protein (sHSP) family, forms large oligomeric structures, and functions as a molecular chaperone appearing very early during embryonic development. To gain mechanistic insight into the structural and functional role of α-crystallin and its alterations in various retinal diseases, it is important to study the interaction chemistry with its known partners. The hydrophobic sites in α-crystallin have been studied extensively using environmentally sensitive fluorescent probes such as 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid dipotassium salt (bis-ANS) that interacts with both subunits of α-cystallin in 1:1 stoichiometry at 37 °C and diminishes the chaperone-like activity of the protein. Furthermore, it has been shown that ATP plays a crucial role in the association of α-crystallin with substrate proteins. We use surface plasmon resonance (SPR) to monitor the interactions of immobilized oligomeric recombinant αA subunit of human α-crystallin protein with bis-ANS and ATP. We assess the thermodynamic parameters and kinetics of such interactions at various temperatures. Our results indicate that bis-ANS binds to αA-crystallin with higher affinity when compared with ATP, although both αA-crystallin and αB-crystallin display fast interaction kinetics.

Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins

Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR) and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA–crystallin (αA N101D and αA N123D) displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET), both αA-deamidated mutants (αA N101D and αA N123D) exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively) compared to WT αA-crystallin (18±4%). Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively) with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE), N-terminal domain (NTD), and core domain (CD) of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin. Variable in vitro and in vivo interactions are most likely due to the mutant’s large size oligomers, reduced hydrophobicity, and altered structures. Together, the results suggest that deamidation of α-crystallin may facilitate greater interaction and the formation of large oligomers with other crystallins, and this may contribute to the cataractogenic mechanism.

Identification of interaction sites between human betaA3- and alphaA/alphaB-crystallins by mammalian two-hybrid and fluorescence resonance energy transfer acceptor photobleaching methods

Our recent study has shown that betaA3-crystallin along with betaB1- and betaB2-crystallins were part of high molecular weight complex obtained from young, old, and cataractous lenses suggesting potential interactions between alpha- and beta-crystallins (Srivastava, O. P., Srivastava, K., and Chaves, J. M. (2008) Mol. Vis. 14, 1872-1885). To investigate this further, this study was carried out to determine the interaction sites of betaA3-crystallin with alphaA- and alphaB-crystallins. The study employed a mammalian two-hybrid method, an in vivo assay to determine the regions of betaA3-crystallin that interact with alphaA- and alphaB-crystallins. Five regional truncated mutants of betaA3-crystallin were generated using specific primers with deletions of N-terminal extension (NT) (named betaA3-NT), N-terminal extension plus motif I (named betaA3-NT + I), N-terminal extension plus motifs I and II (named betaA3-NT + I + II), motif III plus IV (named betaA3-III + IV), and motif IV (named betaA3-IV). The mammalian two-hybrid studies were complemented with fluorescence resonance energy transfer acceptor photobleaching studies using the above described mutant proteins, fused with DsRed (Red) and AcGFP fluorescent proteins. The results showed that the motifs III and IV of betaA3-crystallin were interactive with alphaA-crystallin, and motifs II and III of betaA3-crystallin primarily interacted with alphaB-crystallin.

Free-solution label-free detection of alpha-crystallin chaperone interactions by back-scattering interferometry

We report the quantitative, label-free analysis of protein-protein interactions in free solution within picoliter volumes using backscatter interferometry (BSI). Changes in the refractive index are measured for solutions introduced on a PDMS microchip allowing determination of forward and reverse rate constants for two-mode binding. Time-dependent BSI traces are directly fit using a global analysis approach to characterize the interaction of the small heat-shock protein alpha-Crystallin with two substrates: destabilized mutants of T4 lysozyme and the in vivo target betaB1-Crystallin. The results recapitulate the selectivity of alphaB-Crystallin differentially binding T4L mutants according to their free energies of unfolding. Furthermore, we demonstrate that an alphaA-Crystallin mutant linked to hereditary cataract has activated binding to betaB1-Crystallin. Binding isotherms obtained from steady-state values of the BSI signal yielded meaningful dissociation constants and establishes BSI as a novel tool for the rapid identification of molecular partners using exceedingly small sample quantities under physiological conditions. This work demonstrates that BSI can be extended to screen libraries of disease-related mutants to quantify changes in affinity and/or kinetics of binding.

Interaction between alpha and upsilon-crystallin, common to the eye of the Australian platypus, by radical probe mass spectrometry

The interaction between alpha-crystallin and upsilon-crystallin, a class recently discovered in the eye of the Australian platypus, has been shown by native shift gel assay and examined by radical probe mass spectrometry in the context of the ability of alpha-crystallin to protect upsilon-crystallin from oxidation and oxidative damage through radical-based oxidative stress mechanisms. Residues 22-41, 132-148, 212-227 and 245-264 of upsilon-crystallin display the greatest protection when interacted with alpha-crystallin at a ratio of 2 : 1 observed for the complex, which is commensurate with their levels measured in the eye of the platypus. Across each domain, a delay in the onset of oxidative damage is observed as the time of exposure to radicals is increased. The results are discussed in the context of the structure of the porcine homologue of upsilon-crystallin.

Studies of alphaB crystallin subunit dynamics by surface plasmon resonance

The molecular chaperone activity of alphaB crystallin, an important stress protein in humans, is regulated by physiological factors, including temperature, pH, Ca2+, and ATP. In this study, the role of these factors in regulating the subunit dynamics of human alphaB crystallin was investigated using surface plasmon resonance (SPR). SPR experiments indicate that at temperatures above 37 degrees C, where alphaB crystallin has been reported to have higher chaperone activity, the subunit dynamics of alphaB crystallin were increased with faster association and dissociation rates. SPR experiments also indicate that interactions between alphaB crystallin subunits were enhanced with much faster association and slower dissociation rates at pH values below 7.0, where alphaB crystallin has been reported to have lower chaperone activity. The results suggest that the dynamic and rapid subunit exchange rate may regulate the chaperone activity of alphaB crystallin. The effect of Ca2+ and ATP on the subunit dynamics of alphaB crystallin was minimal, suggesting that Ca2+ and ATP modulate the chaperone activity of alphaB crystallin without altering the subunit dynamics. Based on the SPR results and previously reported biochemical data for the chaperone activity of alphaB crystallin under different conditions of temperature and pH, a model for the relationship between the subunit dynamics and chaperone activity of alphaB crystallin is established. The model is consistent with previous biochemical data for the chaperone activity and subunit dynamics of small heat shock proteins (sHSPs) and establishes a working hypothesis for the relationship between complex assembly and chaperone activity for sHSPs.

Interaction of lens alpha and gamma crystallins during aging of the bovine lens

Heterologous, noncovalent interactions of lens crystallins, such as between alpha and gamma crystallin, are thought to play a key role in the transparent properties of the lens. To determine possible interactions between these two types of crystallins, bovine gamma B crystallin in its native state was purified from whole fetal lenses or from the nucleus of aged bovine lenses, and the purified protein was passed over immobilized alpha crystallin, using a surface plasmon resonance instrument (BIAcore 3000) to obtain refractive units (RU) of gamma B binding at equilibrium. The results demonstrate low binding of gamma B crystallin purified from fetal lenses, but higher binding of the same gamma species purified from aged lenses. Together, these results demonstrate that under equilibrium conditions, gamma B crystallin from the aging bovine lens shows increased noncovalent associations with alpha crystallins, consistent with the possibility that such interactions play an important role in the transparent properties of the aged lens.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.