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Functional roles of the pre-sensor I insertion sequence in an AAA+ bacterial enhancer binding protein

P. Burrows,J. Schumacher,S. Amartey,Tamaswati Ghosh,Timothy A. Burgis,Xiaodong Zhang,B. T. Nixon,M. Buck

Published 2009 in Molecular Microbiology

ABSTRACT

Molecular machines belonging to the AAA+ superfamily of ATPases use NTP hydrolysis to remodel their versatile substrates. The presence of an insertion sequence defines the major phylogenetic pre‐sensor I insertion (pre‐SIi) AAA+ superclade. In the bacterial σ54‐dependent enhancer binding protein phage shock protein F (PspF) the pre‐SIi loop adopts different conformations depending on the nucleotide‐bound state. Single amino acid substitutions within the dynamic pre‐SIi loop of PspF drastically change the ATP hydrolysis parameters, indicating a structural link to the distant hydrolysis site. We used a site‐specific protein–DNA proximity assay to measure the contribution of the pre‐SIi loop in σ54‐dependent transcription and demonstrate that the pre‐SIi loop is a major structural feature mediating nucleotide state‐dependent differential engagement with Eσ54. We suggest that much, if not all, of the action of the pre‐SIi loop is mediated through the L1 loop and relies on a conserved molecular switch, identified in a crystal structure of one pre‐SIi variant and in accordance with the high covariance between some pre‐SIi residues and distinct residues outside the pre‐SIi sequence.

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