PrtD, the integral membrane ATP-binding cassette component of the Erwinia chrysanthemi metalloprotease secretion system, exhibits a secretion signal-regulated ATPase activity.

We have overproduced, partially purified, and characterized PrtD, the ATP-binding cassette (ABC) integral membrane component from the metalloproteases secretion system of the Gram-negative phytopathogenic bacterium Erwinia chrysanthemi. These metalloproteases are secreted independently of the general export pathway encoded by the sec genes. They are secreted via a C-terminal secretion signal and by a secretion apparatus composed of two inner membrane proteins, PrtD and PrtE, and one outer membrane protein PrtF. PrtD is specifically labeled by 8-azido-ATP both in whole membrane vesicles and upon purification. The purified protein displays a low level of P-type ATPase activity. This activity is almost completely and specifically inhibited by the cognate C-terminal secretion signal of the PrtG and PrtB metalloproteases (half inhibition at 0.1 microM) but not by a C-terminal secretion signal of a protein not secreted by the Prt translocator. A mutant PrtD protein bearing a point mutation in the ATP binding site (conserved lysine 370 of the Walker A box changed to arginine) has also been purified. It displays a lower level of ATPase activity which correlates with the lower level of secretion of the metalloproteases by a strain expressing this mutated protein.