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T.B. Estey, A. Pappa, J.F. Carpenter, V. Vasiliou; Studies on the Chaperone-Like Activity of Human Aldehyde Dehydrogenase 3a1 . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1374.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Aldehyde dehydrogenase 3A1 (ALDH3A1) is abundantly expressed in the corneal epithelium of most mammalian species, accounting for 10 to 40% of total water soluble protein. Though the precise biological function of ALDH3A1 remains unclear, many hypotheses address the crucial role of the enzyme in the protection of the cornea and other ocular tissues from UV-induced damage. We have recently shown that human ALDH3A1 is sensitive to UVB-light, which inactivates the enzyme in a time-dependent manner. We also observed structural changes including an increase in surface hydrophobicity and non-covalent oligomerization. Such properties are inherent to the lens crystallins, which are considered molecular chaperones. In the present study, we investigated the potential for human ALDH3A1 to function as a chaperone-like molecule in vitro. Methods: Glucose-6-phosphate dehydrogenase (G6PD) was irradiated with monochromatic UVB-light (295 nm) in the absence and presence of recombinant human ALDH3A1 at various mass ratios. UV-induced damage was assessed by measuring the kinetic activity of the enzyme spectrophotometerically. The ability for human ALDH3A1 to suppress the thermal aggregation of other proteins was investigated by monitoring the increase in light scattering at 360 nm. Results: G6PD is inactivated by UVB-light as a function of the exposure time and nearly 30% of activity lost in the first minute. Low mass ratios of human ALDH3A1 (1:1 and 1:5) do not protect G6PD from UV-induced damage. However, an excess of human ALDH3A1 present during UV-exposure (1:50 to 1:250) resulted in less UV-damage to G6PD. The amount of G6PD inactivation was reduced by 27 to 41% at these mass ratios of human ALDH3A1. Furthermore, no significant reduction in the thermal aggregation of model proteins was observed even at high mass ratios of human ALDH3A1. Conclusions: At high mass ratios, human ALDH3A1 protects G6PD from inactivation by UV-light. However, human ALDH3A1 cannot suppress the thermal aggregation of model proteins. Our findings suggest that human ALDH3A1 does not function as a molecular chaperone to the extent observed with the lens crystallins. Rather, competition for free radical species and UV-light energy may be the mechanism of ALDH3A1 protection.
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