Because many proteins that localize to specific organelles must fold correctly in order to be trafficked properly, mutations that destabilize the correct fold can lead to improper subcellular localization.
In the present study we wanted to elucidate the structural bases, if any, that determine whether or not a mutant would undergo proper trafficking to cell membrane and, if trafficked properly, whether or not it would lead to complete or partial alteration of gap junction channel conductance.
Our study shows that it is important to perform measurements to identify the relation between power consumption and traffic properly.
Thus, these mutant HCN4 channels traffic properly, despite producing no current, possibly as a result of large voltage shifts in the channel activation.
For example, under highly-expressing cell conditions, much Phe508del-CFTR fails to traffic properly, and it is expressed in very low levels at the airway surface cell membrane (as opposed to glands).
Thus neither of these mutants alters surface electrostatic potential, and hence, both of these traffic properly (as Cx50-W45S).
G46V (located in EC1) traffics properly and shows similar gap junction conductance but higher hemichannel currents than WT Cx50 probably leading to apoptosis of the cells [ 27, 28].
Again, Cx26-D46E (corresponding to Cx50-D47N) was found to traffic properly although it showed disruption of both ionic and biochemical coupling [ 35].
Among these, 5 mutations undergo impaired intracellular trafficking (i.e., R23T, D47N, P88S/Q, and R205G[Gja8]) while 2 mutations (i.e., V44E and W45S) traffic properly to cell membrane; trafficking of E48K has not been reported yet.
This mutant (located in TM2) has been reported to traffic properly and form functional homotypic and heteromeric intercellular channels (with Cx46 and Cx50); however, it caused alteration in voltage gating and a dramatic reduction in the single-channel open probability, resulting in reduced levels of conductance [ 21].
These preparations of purified membranes enriched for connexin hemichannels that have been properly trafficked and inserted in membranes provide a platform for high-resolution AFM imaging of the structure, interconnexon interactions, and cooperativity of properly trafficked and inserted noncrystalline connexin hemichannels.
