AglU, a protein required for gliding motility and spore maturation of Myxococcus xanthus, is related to WD-repeat proteins

The aglU gene of Myxococcus xanthus encodes a protein similar to Het-E1 (vegetative incompatibility) from Podospora anserina, acylaminoacyl-peptidase from Bacillus subtilis, and TolB from Escherichia coli. These proteins all have evenly spaced SPDG repeats that are characteristic of a larger motif called the WD-repeat. The WD-repeat is predicted to form a beta-propeller structure that mediates the assembly of heteromeric protein complexes. AglU has a consensus lipoprotein attachment motif that includes a type II signal sequence followed by a cysteine residue. This suggests that AglU is matured, then attached to the outer membrane via fatty acid acylation at this Cys. Cells carrying a mutation in aglU are blocked in adventurous gliding and can swarm only if cells are in contact with one another. When starved of nutrients, the aglU mutant aggregates and forms multicellular fruiting bodies like the wild-type strain, but is unable to produce heat-resistant spores. This suggests that adventurous gliding motility, per se, is not required for development, but that AglU is essential for a terminal step of spore differentiation.