Jonathan Alan King, Dept of Biology, MIT, Cambridge, MA 02139
The transparency of the eye lens depends on maintenance of the native state of the Greek key γ and Β crystallins. The γD-crystallins in the central core of the lens, are synthesized during infancy, and are among the longest-lived proteins in the body. Cataract, the leading cause of blindness worldwide, involves the polymerization of covalently damaged or partially unfolded conformations of the lens crystallins into aggregates large enough to scatter visible light. Congenital cataracts are associated with a number of single amino acid substitutions in γD-crystallin and other lens crystallins. We have studied the in vitro folding, unfolding and aggregation of diverse mutant Human γD-crystallins. Those mimicking oxidative damage, exhibit properties accounting for the cataract phenotype. These experiments have been aided by unusual fluorescence properties of the four buried and conserved tryptophan residues in Βγ-crystallins. The transition from a soluble well-folded Β-sheet to the polymerized state appears to proceeds through a domain-swapping mechanism. This depends on transient stabilization of a distinctive partially-unfolded Β-sheet intermediate induced in the mutant protein by temperatures at and above physiological and involves some unexpected thiol chemistry.
Chen, J., Callis, P.R., and King, J. 2009. Mechanism of the very efficient quenching of tryptophan fluorescence in human γD- and γS-crystallins: the gamma-crystallin fold may have evolved to protect tryptophan residues from ultraviolet photodamage.Biochemistry 48(17): 3708-3716.
Acosta-Sampson, L. and King, J. 2010. Partially folded aggregation intermediates of human γD-, γC-, and γS-crystallin are recognized and bound by human αβ-crystallin chaperone. J Mol Biol 401(1): 134-152.
Moreau, K.L. and King, J. 2009. Hydrophobic Core Mutations Associated with Cataract Development in Mice Destabilize Human D-Crystallin. Journal of Biological Chemistry 284(48): 33285-33295.
Serebryany E and King JA (2015) Wild-type human γD-crystallin promotes aggregation of its oxidation-mimicking, misfolding-prone W42Q mutant. J Biol Chem, 290(18): 11491-11503.