Interactions of a Bacterial RND Transporter with a Transmembrane Small Protein in a Lipid Environment.

The small protein AcrZ in Escherichia coli interacts with the transmembrane portion of the multidrug efflux pump AcrB and increases resistance of the bacterium to a subset of the antibiotic substrates of that transporter. It is not clear how the physical association of the two proteins selectively changes activity of the pump for defined substrates. Here, we report cryo-EM structures of AcrB and the AcrBZ complex in lipid environments, and comparisons suggest that conformational changes occur in the drug-binding pocket as a result of AcrZ binding.

Alternative ORFs and small ORFs: shedding light on the dark proteome.

Traditional annotation of protein-encoding genes relied on assumptions, such as one open reading frame (ORF) encodes one protein and minimal lengths for translated proteins. With the serendipitous discoveries of translated ORFs encoded upstream and downstream of annotated ORFs, from alternative start sites nested within annotated ORFs and from RNAs previously considered noncoding, it is becoming clear that these initial assumptions are incorrect. The findings have led to the realization that genetic information is more densely coded and that the proteome is more complex than previously anticipated.

The small protein MgtS and small RNA MgrR modulate the PitA phosphate symporter to boost intracellular magnesium levels.

In response to low levels of magnesium (Mg ), the PhoQP two component system induces the transcription of two convergent genes, one encoding a 31-amino acid protein denoted MgtS and the second encoding a small, regulatory RNA (sRNA) denoted MgrR. Previous studies showed that the MgtS protein interacts with and stabilizes the MgtA Mg importer to increase intracellular Mg levels, while the MgrR sRNA base pairs with the eptB mRNA thus affecting lipopolysaccharide modification. Surprisingly, we found overexpression of the MgtS protein also leads to induction of the PhoRB regulon.

Increasing intracellular magnesium levels with the 31-amino acid MgtS protein.

Synthesis of the 31-amino acid, inner membrane protein MgtS (formerly denoted YneM) is induced by very low Mg in a PhoPQ-dependent manner in Here we report that MgtS acts to increase intracellular Mg levels and maintain cell integrity upon Mg depletion. Upon development of a functional tagged derivative of MgtS, we found that MgtS interacts with MgtA to increase the levels of this P-type ATPase Mg transporter under Mg-limiting conditions. Correspondingly, the effects of MgtS upon Mg limitation are lost in a ∆ mutant, and MgtA overexpression can suppress the ∆ phenotype.