Structure-Function Correlation Analysis of Connexin50 Missense Mutations Causing Congenital Cataract: Electrostatic Potential Alteration Could Determine Intracellular Trafficking Fate of Mutants

Abstract

Connexin50 (Cx50) mutations are reported to cause congenital cataract probably through the disruption of intercellular transport in the lens. Cx50 mutants that undergo mistrafficking have generally been associated with failure to form functional gap junction channels; however, sometimes even properly trafficked mutants were found to undergo similar consequences. We hereby wanted to elucidate any structural bases of the varied functional consequences of Cx50 missense mutations through in silico approach. Computational studies have been done based on a Cx50 homology model to assess conservation, solvent accessibility, and 3-dimensional localization of mutated residues as well as mutation-induced changes in surface electrostatic potential, H-bonding, and steric clash. This was supplemented with meta-analysis of published literature on the functional properties of connexin missense mutations. Analyses revealed that the mutation-induced critical alterations of surface electrostatic potential in Cx50 mutants could determine their fate in intracellular trafficking. A similar pattern was observed in case of mutations involving corresponding conserved residues in other connexins also. Based on these results the trafficking fates of 10 uncharacterized Cx50 mutations have been predicted. Further experimental analyses are needed to validate the observed correlation.

Charged Residues at the First Transmembrane Region Contribute to the Voltage Dependence of the Slow Gate of Connexins

“…It has been proposed that the surface electrostatic profile on the extracellular face of Cx50 is crucial for the trafficking of the hemichannel to the plasma membrane. It is likely that some of the mutations introduced affected the trafficking of the hemichannel, and consequently, we could not observe any hemichannel currents (40).…”

Characterization of a variant of gap junction protein α8 identified in a family with hereditary cataract

“…Ours is the first study to characterize the consequences of the N220D variant on the biochemical and functional properties of Cx50. The most common pathogenic mechanism found in other cataract-associated Cx50 mutants is failure to form gap junctions due to impaired protein folding and/or localization to the plasma membrane [ 6 , 15 , 16 ]. Unlike most pathogenic mutations, Cx50 N220D localized to appositional plasma membranes and formed functional gap junction plaques between adjacent cells.…”

Focus on lens connexins

“…The crystal structure of Cx26 may also be useful in predicting conformational changes affecting protein folding in some mutants and trafficking (by calculating the surface electrostatic potential [ 58 ]). However, it may not be able to predict mutations affecting internalization or degradation.…”