Interaction of FliI, a component of the flagellar export apparatus, with flagellin and hook protein

FliI is a key component of the flagellar export apparatus in Salmonella typ himurium. It catalyzes the hydrolysis of ATP which is necessary for flagell ar assembly. Affinity blotting experiments showed that purified flagellin a nd hook protein, two flagellar axial proteins, interact specifically with F liI. The interaction of either of the two proteins with FliI, increases the intrinsic ATPase activity. The presence of either flagellin or hook protei n stimulates ATPase activity in a specific and reversible manner. A V-max o f 0.12 nmol P-i min(-1) mu g(-1) and a K-m for MgATP of 0.35 mM was determi ned for the unstimulated FliI; the presence of flagellin increased the V-ma x to 0.35 nmol P-i min(-1) mu g(-1) and the K-m for MgATP to 1.1 mM. The st imulation induced by the axial proteins was fully reversible suggesting a d irect link between the catalytic activity of FliI and the export process. ( C) 1999 Elsevier Science B.V. All rights reserved.