Characterization of the G91del CRYBA1/3-crystallin protein: a cause of human inherited cataract

Abstract

Congenital cataract is a leading cause of visual disability in children. Inherited isolated (non-syndromic) cataract represents a significant proportion of cases and the identification of genes responsible for inherited cataract will lead to a better understanding of the mechanism of cataract formation at the molecular level both in congenital and age-related cataract. Crystallins are abundantly expressed in the developing human lens and represent excellent candidate genes for inherited cataract. A genome-wide search of a five-generation family with autosomal dominant lamellar cataract demonstrated linkage to the 17p12-q11 region. Screening of the CRYBA1/3 gene showed a 3 bp deletion, which resulted in a G91del mutation within the tyrosine corner, that co-segregated with disease and was not found in 96 normal controls. In order to understand the molecular basis of cataract formation, the mutant protein was expressed in vitro and its unfolding and refolding characteristics assessed using far-UV circular dichroism spectroscopy. Defective folding and a reduction in solubility were found. As the wild-type protein did not refold into the native conformation following unfolding, a corresponding CRYBB2 mutant was genetically engineered and its refolding characteristics analysed and compared with wild-type CRYBB2. Its biophysical properties support the hypothesis that removal of the glycine residue from the tyrosine corner impairs the folding and solubility of beta-crystallin proteins. This study represents the first comprehensive description of the biophysical consequences of a mutant beta-crystallin protein that is associated with human inherited cataract.

βA3/A1-crystallin in astroglial cells regulates retinal vascular remodeling during development

“…This mutation results in a semi-dominant nuclear cataract phenotype (Graw et al, 1999). There are five reports of human mutations in βA3/A1-crystallin, all with dominant or semi-dominant cataract phenotypes (Kannabiran et al, 1998;Bateman et al, 2000;Qi et al, 2004;Ferrini et al, 2004;Reddy et al, 2004). Two of the mutations are at the five prime (donor) splice site of intron 3.…”

“…This interval contained 49 genes identified through the reference sequence annotation database for the rat genome assembly, which we augmented by alignment with the mouse and human genomes. One of the genes was the βA3/A1-crystallin gene, which has been shown to cause congenital cataracts when mutated (Kannabiran et al, 1998;Bateman et al, 2000;Qi et al, 2004;Ferrini et al, 2004;Reddy et al, 2004;Graw et al, 1999). This gene was sequenced and the mutation was identified as a 27 base insertion in the 6th exon.…”

“…Both polypeptides are affected by the Nuc1 mutation. Mutations in βA3/A1-crystallin are well known to cause cataract in both humans and mice (Kannabiran et al, 1998;Bateman et al, 2000;Qi et al, 2004;Ferrini et al, 2004;Reddy et al, 2004;Graw et al, 1999). In Nuc1 homozygotes, however, in addition to cataracts, severe retinal and other ocular abnormalities are apparent Hose et al, 2005;Zhang et al, 2005;Gehlbach et al, 2006).…”

Pediatric cataracts: clinical aspects, frequency of strabismus and chronological, etiological, and morphological features

“…Accordingly, mutations in crystallins and connexins have been identified to play important role in the development of cataracts. To date, more than 30 independent loci have been mapped and identified as playing key roles in inherited cataracts (21)(22)(23)(24)(25) . Other measures that could improve the identification of the etiology of pediatric cataracts include a questionnaire regarding exposure to environmental risk factors or chemicals and implementation of polymerase chain reaction (PCR)-based tests to detect viral infection of the lens.…”

The genetic and molecular basis of congenital cataract

“…The β-crystallin family consists of four acidic and three basic forms depending on the isoelectric point and the terminal extensions. The basic (βB) members of this group contain C-terminal extensions, while the acidic members (βA) do not have this extension (34) . The β/ϒ-crystallins proteins are proteins that share a "Greek Key" (GK) motif unit base.…”