Abstract
The localization of hook-associated proteins (HAP1, HAP2, and HAP3) in Salmonella typhimurium flagella was studied by using specific antibodies together with a second antibody conjugated with colloidal gold. HAP1 and HAP3 were localized at the hook-filament junction, as has been suggested previously. HAP2, however, was localized at the filament tip. This finding supports the idea that HAP2 acts to induce polymerization of endogenous flagellin at the filament tip, and HAP1 and HAP3 are junction proteins to connect hook with filament. Analysis of the protein composition of short flagella from a mutant indicated that a single flagellum contains about 10 to 20 HAP1, 10 to 20 HAP2, and 10 to 40 HAP3 molecules.
Highlights
A bacterial flagellum consists of three distinct parts connected in series: a basal body in the membrane, a short curved rod called the hook, and a long helical filament
We found that HAP2 is located at the tip, whereas both HAP1 and HAP3 are at the hook-filament junction, in agreement with a model previously presented [7]
We have shown that HAP2 is localized at the flagellar tip whereas HAP1 and HAP3 are located at the hook-filament junction
Summary
A bacterial flagellum consists of three distinct parts connected in series: a basal body in the membrane, a short curved rod called the hook, and a long helical filament (see for review reference 21). Salmonella typhimurium mutants defective in the structural genes for flagellin (HI and H2) or in certain other genes (flaL, flaU, flaV, and flaW) have hooks but not filaments [11] By study of such mutants, Homma et al have found three proteins (HAP1, HAP2, and HAP3) associated with the hook [11]. The same phenomenon was observed withflaV mutants on which short flagellar filaments had been grown by the addition of exogenous flagellin [9] These findings suggest that, in wild-type flagella, HAP2 is attached to the flagellar tip, somehow working to trap and assemble endogenous flagellin and to prevent the addition of exogenous flagellin. These findings indicate that filament growth in vivo is a complex process that involves flagellin-HAP2 interaction in addition to flagellin-flagellin interaction
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