A TACTILE SENSORY SYSTEM OF MYXOCOCCUS-XANTHUS INVOLVES AN EXTRACELLULAR NAD(P)(-CONTAINING PROTEIN())

CsgA is a cell surface protein that plays an essential role in tactile responses during Myxococcus xanthus fruiting body formation by produc ing the morphogenic C-signal. The primary amino acid sequence of CsgA exhibits homology with members of the short-chain alcohol dehydrogenas e (SCAD) family and several lines of evidence suggest that NAD(P)(+) b inding is essential for biological activity. First, the predicted CsgA . secondary structure based on the 3 alpha/20 beta-hydroxysteroid dehy drogenase crystal structure suggests that the amino-terminal portion o f the protein contains an NAD(P)(+) binding pocket. Second, strains wi th csgA alleles encoding amino acid substitutions T6A and R10A in the NAD(P)(+) binding pocket failed to develop. Third, exogenous MalE-CsgA rescues csgA development, whereas MalG-CsgA with the amino acid subst itution CsgA T6A does not. Finally, csgA spore yield increased similar to 20% when buffer containing 100 nM of MalG-CsgA was supplemented wi th 10 mu M of NAD(+) or NADP(+). Conversely, 10 mu M of NADH or NADPH delayed development for similar to 24 hr and depressed spore levels si milar to 10%. Together, these results argue that NAD(P)(+) binding is critical for C-signaling. S135 and K155 are conserved amino acids in t he catalytic domain of SCAD members. Strains with csgA alleles encodin g the amino acid substitutions S135T or K155R failed to develop. Furth ermore, a MalE-CsgA protein containing CsgA S135T was not able to rest ore development to csgA cells. In conclusion, amino acids conserved in the coenzyme binding pocket and catalytic site are essential for C-si gnaling.