Alterations at Arg76 of human connexin 46, a residue associated with cataract formation, cause loss of gap junction formation but preserve hemichannel function

The connexins are members of a family of integral membrane proteins which form gap junction channels between apposed cells and/or hemichannels across the plasma membranes. The importance of the Arginine at position 76 (Arg76) in the structure and/or function of Cx46 is highlighted by its conservation across the entire connexin family and the occurrence of pathogenic mutations at this (or the corresponding homologous) residue in a number of human diseases. Two mutations at Arg76 in Cx46 are associated with cataracts in humans, highlighting the importance of this residue. We examined the expression levels and macroscopic and single channel properties of human Cx46 and compared them to those for two pathogenic mutants, namely R76H and R76G. To gain further insight into the role of charge at this position, we generated two additional non-naturally occurring mutants, R76K (charge-conserving) and R76E (charge-inverting). We found that when expressed exogenously in Neuro2a cells, all four mutants formed membrane...