A novel mutation in CRYBB1 associated with congenital cataract-microcornea syndrome: the p.Ser129Arg mutation destabilizes the βB1/βA3-crystallin heteromer but not the βB1-crystallin homomer

Abstract

Congenital cataract-microcornea syndrome (CCMC) is a clinically and genetically heterogeneous condition characterized by lens opacities and microcornea. It appears as a distinct phenotype of heritable congenital cataract. Here we report a large Chinese family with autosomal dominant congenital cataract and microcornea. Evidence for linkage was detected at marker D22S1167 (LOD score [Z]=4.49, recombination fraction [θ]=0.0), which closely flanks the â-crystallin gene cluster locus. Direct sequencing of the candidate âB1-crystallin gene (CRYBB1) revealed a c.387C>A transversion in exon 4, which cosegregated with the disease in the family and resulted in the substitution of serine by arginine at codon 129 (p.Ser129Arg). A comparison of the biophysical properties of the recombinant β-crystallins revealed that the mutation impaired the structures of both βB1-crystallin homomer and βB1/βA3-crystallin heteromer. More importantly, the mutation significantly decreased the thermal stability of βB1/βA3-crystallin but not βB1-crystallin. These findings highlight the importance of protein-protein interactions among β-crystallins in maintaining lens transparency, and provide a novel insight into the molecular mechanism underlying the pathogenesis of human CCMC. © 2011 Wiley-Liss, Inc.

A novel Cx50 (GJA8) p.H277Y mutation associated with autosomal dominant congenital cataract identified with targeted next-generation sequencing

“…Nearly one third of the cases have a genetic basis [5]. It can present in an isolated manner or may occur in association with other ocular or systemic diseases [1,6].…”

“…Congenital cataract is the leading cause of reversible blindness in childhood and accounts for one tenth of the cases of childhood blindness [1]. Its prevalence, depending on the regional socioeconomic development, is estimated to vary from 0.6 to six cases per 10,000 live births in industrialized countries [2,3], and from five to 15 per 10,000 in the poorest areas of the world [4].…”

Cataract-causing mutation R233H affects the stabilities of βB1- and βA3/βB1-crystallins with different pH-dependence

“…S129R has been shown to increase the stability and decrease the aggregatory propensity of βB1 homomer [45]. If assuming that the protecting effect of βB1 on acidic β-crystallins is one of the functions of βB1, Ser129 is more likely to be a functional residue contributed to heteromer assembly and stability [42,45]. In this research, we proposed that Arg233 was another functional residue in βB1 based on the dissimilar effects of the R233H mutation on βB1 and βA3/βB1.…”

“…The pET28a plasmids containing the wild type (WT) human βB1 and βA3 genes (CRYBB1 and CRYBA3, respectively) were constructed as that described previously [42]. Site-directed mutagenesis for R233H was performed using the following primers: forward, 5′-GCGTCGCCTGCA TGACAAGCAGT-3′ and reverse, 5′-ACTGCTTGTCATGCAGGCGACGC-3′, respectively.…”

“…Moreover, β-crystallins also have a high expression in some non-lens tissues, implying that β-crystallins may have important physiological functions other than acting as structural proteins in the lens [16,17,19,[35][36][37]. Besides those mechanisms shared by γ-crystallin mutations [38][39][40][41], β-crystallin mutations have been proposed to be able to dissociate the homomers [42][43][44][45], weaken the heteromer assembly [42,44,45] or disrupt the dynamic oligomeric equilibrium [38].…”