Structural and Functional Peculiarities of α-Crystallin

Abstract

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.

Dynamic fibrillar assembly of αB-crystallin induced by perturbation of the conserved NT-IXI motif resolved by cryo-EM

“…The fraction showing elution overlap with αB-wt mainly consisted of spherical oligomers, measuring approximately 14–16 nm in diameter ( Fig. 1c , *), consistent with previous characterizations of αB-wt 16,41,44,45 (see also Extended Data Fig. 2 ).…”

An AFM Approach Applied in a Study of α-Crystallin Membrane Association: New Insights into Lens Hardening and Presbyopia Development

“…As expected, polydisperse α-crystallin oligomers and a close association of such oligomers are seen. Interestingly, a comparable image of negatively stained bovine lens α-crystallin was reported previously using an electron microscope [ 65 ]. The present paper reports AFM imaging of α-crystallin oligomers ( Figure 5 ) for the first time.…”

Alpha-B-Crystallin Effect on Mature Amyloid Fibrils: Different Degradation Mechanisms and Changes in Cytotoxicity

“…According to the literature, alpha-B-crystallin in physiological conditions has a highly heterogeneous nature. The modeling based on the electron microscopy analysis of alpha-crystallin shows that the main population of the alpha-B-crystallin polydisperse complex is represented by oligomeric particles of slightly ellipsoidal shape with a diameter of about 13.5 nm and a molecular mass of about 700 kDa [ 52 ]. The results obtained by us are in a good agreement with the literature ( Figure S3 ).…”