Two distinct levels of gap junction assembly in vitro.

The in vitro assembly of crystalline gap junctions from detergent-solubilized sheep lens fiber cell pore complexes in the presence of endogenous lipid is a two-step process. "Mini"-gap junctions containing about 10 pore complexes assembled within 12 hr of dialysis. The removal of detergent appeared to be the sole factor required to reach this level of assembly. Further growth to micrometer-sized crystalline gap junctions required cleaved connexin, MgCl2, elevated dialysis temperature, and dialysis for 3-5 days. Molecular interactions between adjacent pore structures laterally in the membrane are vital for the second phase of assembly but appear to be of minor importance for the formation of mini-gap junctions. Parallels exist between structural aspects of gap junction assembly in vitro and the 2-D crystallization of membrane proteins in general.