Summarya-Crystallin, a prominent member of small heat shock protein (sHsp) family and a major structural protein of the eye lens is a large polydisperse oligomer of two isoforms, aA-and aB-crystallins. Numerous studies have demonstrated that a-crystallin functions like a molecular chaperone in preventing the aggregation of various proteins under a wide range of stress conditions. The molecular chaperone function of a-crystallin is thus considered to be vital in the maintenance of lens transparency and in cataract prevention. a-Crystallin selectively interacts with non-native proteins thereby preventing them from aggregation and helps maintain them in a folding competent state. It has been proposed and generally accepted that a-crystallin suppresses the aggregation of other proteins through the interaction between hydrophobic patches on its surface and exposed hydrophobic sites of partially unfolded substrate protein. However, a quantifiable relationship between hydrophobicity and chaperone-like activity remains a matter to be concerned about. On an attentive review of studies on a-crystallin chaperonelike activity, particularly the studies that have direct or indirect implications to hydrophobicity and chaperone-like activity, we found several instances wherein the correlation between hydrophobicity and its chaperone-like activity is paradoxical. We thus attempted to provide an overview on the role of hydrophobicity in chaperone-like activity of a-crystallin, the kind of evaluation done for the first time. IUBMB Life, 58: 632-641, 2006

I.V. ketamine (250 microg kg(-1)) is an effective treatment for reducing the incidence and severity of postoperative CRBD.

Alpha-crystallin is a member of the small heat-shock protein family and functions like a molecular chaperone, and may thus help in maintaining the transparency of the eye lens by protecting the lens proteins from various stress conditions. Non-enzymic glycation of long-lived proteins has been implicated in several age- and diabetes-related complications, including cataract. Dicarbonyl compounds such as methylglyoxal and glyoxal have been identified as the predominant source for the formation of advanced glycation end-products in various tissues including the lens. We have investigated the effect of non-enzymic browning of alpha-crystallin by reactive dicarbonyls on its molecular chaperone-like function. Non-enzymic browning of bovine alpha-crystallin in vitro caused, along with altered secondary and tertiary structures, cross-linking and high-molecular-mass aggregation. Notwithstanding these structural changes, methylglyoxal- and glyoxal-modified alpha-crystallin showed enhanced anti-aggregation activity in various in vitro aggregation assays. Paradoxically, increased chaperone-like activity of modified alpha-crystallin was not associated with increased surface hydrophobicity and rather showed less 8-anilinonaphthalene-l-sulphonic acid binding. In contrast, the chaperone-like function of modified alpha-crystallin was found to be reduced in assays that monitor the prevention of enzyme inactivation by UV-B and heat. Moreover, incubation of bovine lens with methylglyoxal in organ culture resulted in cataract formation with accumulation of advanced glycation end-products and recovery of alpha-crystallin in high proportions in the insoluble fraction. Furthermore, soluble alpha-crystallin from methylglyoxal-treated lenses showed decreased chaperone-like activity. Thus, in addition to describing the effects of methylglyoxal and glyoxal on structure and chaperone-like activity, our studies also bring out an important caveat of aggregation assays in the context of the chaperone function of alpha-crystallin.

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The chaperone-like activity of alpha-crystallin is considered to play an important role in the maintenance of the transparency of the eye lens. However, in the case of aging and in diabetes, the chaperone function of alpha-crystallin is compromized, resulting in cataract formation. Several post-translational modifications, including non-enzymatic glycation, have been shown to affect the chaperone function of alpha-crystallin in aging and in diabetes. A variety of agents have been identified as the predominant sources for the formation of AGEs (advanced glycation end-products) in various tissues, including the lens. Nevertheless, glycation of alpha-crystallin with various sugars has resulted in divergent results. In the present in vitro study, we have investigated the effect of glucose, fructose, G6P (glucose 6-phosphate) and MGO (methylglyoxal), which represent the major classes of glycating agents, on the structure and chaperone function of alpha-crystallin. Modification of alpha-crystallin with all four agents resulted in the formation of glycated protein, increased AGE fluorescence, protein cross-linking and HMM (high-molecular-mass) aggregation. Interestingly, these glycation-related profiles were found to vary with different glycating agents. For instance, CML [N(epsilon)-(carboxymethyl)lysine] was the predominant AGE formed upon glycation of alpha-crystallin with these agents. Although fructose and MGO caused significant conformational changes, there were no significant structural perturbations with glucose and G6P. With the exception of MGO modification, glycation with other sugars resulted in decreased chaperone activity in aggregation assays. However, modification with all four sugars led to the loss of chaperone activity as assessed using an enzyme inactivation assay. Glycation-induced loss of alpha-crystallin chaperone activity was associated with decreased hydrophobicity. Furthermore, alpha-crystallin isolated from glycated TSP (total lens soluble protein) had also increased AGE fluorescence, CML formation and diminished chaperone activity. These results indicate the susceptibility of alpha-crystallin to non-enzymatic glycation by various sugars and their derivatives, whose levels are elevated in diabetes. We also describe the effects of glycation on the structure and chaperone-like activity of alpha-crystallin.

Venipuncture is the most common painful event for a hospitalized child. We evaluated the efficacy of balloon inflation for attenuating venipuncture pain in children. Seventy-five pediatric patients aged 6-12 yr, ASA physical status I-II, of either sex, undergoing elective surgery were included in this prospective and randomized study. Patients were randomly divided into 3 equal groups of 25 each; Group I (control), Group II (distraction) pressed a rubber ball, and Group III (balloon) inflated a balloon. A manual venous occlusion was applied on the forearm and venipuncture was performed with a 22-gauge venous cannula. Pain was self-reported by a pain face scale with a 10-cm visual analog scale (VAS) placed at its back, where 0 = "no pain" and 10 = "worst imaginable pain." VAS scores of 1-3 were rated as mild, 4-6 as moderate, and >6 as severe. Median (interquartile range) VAS score in the balloon group was 1 (3), which was reduced as compared with 2 (2) and 4 (2) observed in the distraction and control groups, respectively (P < 0.000). Significant reduction in the incidence and severity of venipuncture pain was also observed in the balloon group compared with the other 2 groups (P < 0.05).

The causal role of aneuploidy in cancer initiation remains under debate since mutations of euploidy-controlling genes reduce cell fitness but aneuploidy strongly associates with human cancers. Telomerase activation allows immortal growth by stabilizing telomere length, but its role in aneuploidy survival has not been characterized. Here, we analyze the response of primary human cells and murine hematopoietic stem cells (HSCs) to aneuploidy induction and the role of telomeres and the telomerase in this process. The study shows that aneuploidy induces replication stress at telomeres leading to telomeric DNA damage and p53 activation. This results in p53/Rb-dependent, premature senescence of human fibroblast, and in the depletion of hematopoietic cells in telomerase-deficient mice. Endogenous telomerase expression in HSCs and enforced expression of telomerase in human fibroblasts are sufficient to abrogate aneuploidy-induced replication stress at telomeres and the consequent induction of premature senescence and hematopoietic cell depletion. Together, these results identify telomerase as an aneuploidy survival factor in mammalian cells based on its capacity to alleviate telomere replication stress in response to aneuploidy induction.

␣-Crystallin, composed of two subunits, ␣A and ␣B, has been shown to function as a molecular chaperone that prevents aggregation of other proteins under stress conditions. The exposed hydrophobic surfaces of ␣-crystallins have been implicated in this process, but their exact role has not been elucidated. In this study, we quantify the hydrophobic surfaces of ␣A-and ␣B-crystallins by isothermal titration calorimetry using 8-anilino-1-napthalenesulfonic acid (ANS) as a hydrophobic probe and analyze its correlation to the chaperone potential of ␣A-and ␣B-crystallins under various conditions. Two ANS binding sites, one with low and another with high affinity, were clearly detected, with ␣B showing a higher number of sites than ␣A at 30°C. In agreement with the higher number of hydrophobic sites, ␣B-crystallin demonstrated higher chaperone activity than ␣A at this temperature. Thermodynamic analysis of ANS binding to ␣A-and ␣B-crystallins indicates that high affinity binding is driven by both enthalpy and entropy changes, with entropy dominating the low affinity binding. Interestingly, although the number of ANS binding sites was similar for ␣A and ␣B at 15°C, ␣A was more potent than ␣B in preventing aggregation of the insulin B-chain. Although there was no change in the number of high affinity binding sites of ␣A and ␣B for ANS upon preheating, there was an increase in the number of low affinity sites of ␣A and ␣B. Preheated ␣A, in contrast to ␣B, exhibited remarkably enhanced chaperone activity. Our results indicate that although hydrophobicity appears to be a factor in determining the chaperone-like activity of ␣-crystallins, it does not quantitatively correlate with the chaperone function of ␣-crystallins.