1.A.34 The Bacillus Gap Junction-like Channel-forming Complex (GJ-CC) Family

SpoIIQ and SpoIIIAH (See 9.B.70.1.1) have been reported to form a channel connecting the B. subtilis mother cell to the pre-forespore. SpoIIIAA-AH are encoded within a single operon and may function as a protein secretion system. SpoIIQ and SpoIIAA-AH are produced in the mother cell under σE control and are normally required for activation of σG in the forespore by σE in the mother cell. Possibly these two proteins form a channel linking the two compartments of the Bacillus sporangium (Camp and Losick, 2008).

Meisner et al., 2008 showed that SpoIIIAH is targeted to the forespore membrane. Both SpoIIIAH (218 aas) and SpoIIQ (283 aas) have single N-terminal TMSs with the bulk of the protein on the outside. They have affinity for each other in their extracytoplasmic domains. Consquently they may abut each other to form a trans 2-membrane pore, allowing the mother cell to feed and signal to the forespore. The pore appears to be large enough to transport proteins.

SpoIIIAH is similar to YscJ/FliF of the type III and flagellar systems of enteric bacteria, and like them, forms ring structures (Meisner et al., 2008). Camp and Losick, 2009 have suggested that the channel formed by SpoIIQ and SpoIIIAH is like a 'feeding tube', like a gap junction of animal cells (see also Kroos, 2009).

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