In vivo substrates of the lens molecular chaperones ?A-crystallin and ?B-crystallin.

ABSTRACT: ?A-crystallin and ?B-crystallin are members of the small heat shock protein family and function as molecular chaperones and major lens structural proteins. Although numerous studies have examined their chaperone-like activities in vitro, little is known about the proteins they protect in vivo. To elucidate the relationships between chaperone function, substrate binding, and human cataract formation, we used proteomic and mass spectrometric methods to analyze the effect of mutations associated with hereditary human cataract formation on protein abundance in ?A-R49C and ?B-R120G knock-in mutant lenses. Compared with age-matched wild type lenses, 2-day-old ?A-R49C heterozygous lenses demonstrated the following: increased crosslinking (15-fold) and degradation (2.6-fold) of ?A-crystallin; increased association between ?A-crystallin and filensin, actin, or creatine kinase B; increased acidification of ?B1-crystallin; increased levels of grifin; and an association between ?A3/A1-crystallin and ?A-crystallin. Homozygous ?A-R49C mutant lenses exhibited increased associations between ?A-crystallin and ?B3-, ?A4-, ?A2-crystallins, and grifin, whereas levels of ?B1-crystallin, gelsolin, and calpain 3 decreased. The amount of degraded glutamate dehydrogenase, ?-enolase, and cytochrome c increased more than 50-fold in homozygous ?A-R49C mutant lenses. In ?B-R120G mouse lenses, our analyses identified decreased abundance of phosphoglycerate mutase, several ?- and ?-crystallins, and degradation of ?A- and ?B-crystallin early in cataract development. Changes in the abundance of hemoglobin and histones with the loss of normal ?-crystallin chaperone function suggest that these proteins also play important roles in the biochemical mechanisms of hereditary cataracts. Together, these studies offer a novel insight into the putative in vivo substrates of ?A- and ?B-crystallin.

SUBMITTER: Andley UP 

PROVIDER: S-EPMC3997384 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature