Defining the mRNA recognition signature of a bacterial toxin protein.
Bacteria contain multiple type II toxins that selectively degrade mRNAs bound to the ribosome to regulate translation and growth and facilitate survival during the stringent response. Ribosome-dependent toxins recognize a variety of three-nucleotide codons within the aminoacyl (A) site, but how these endonucleases achieve substrate specificity remains poorly understood. Here, we identify the critical features for how the host inhibition of growth B (HigB) toxin recognizes each of the three A-site nucleotides for cleavage. X-ray crystal structures of HigB bound to two different codons on the ribosome illustrate how HigB uses a microbial RNase-like nucleotide recognition loop to recognize either cytosine or adenosine at the second A-site position. Strikingly, a single HigB residue and 16S rRNA residue C1054 form an adenosine-specific pocket at the third A-site nucleotide, in contrast to how tRNAs decode mRNA. Our results demonstrate that the most important determinant for mRNA cleavage by ribosome-dependent toxins is interaction with the third A-site nucleotide.
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
Marc A
MA
Schureck
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
Jack A
JA
Dunkle
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
Tatsuya
T
Maehigashi
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
Stacey J
SJ
Miles
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322 christine.m.dunham@emory.edu.
Christine M
CM
Dunham
D001427:Bacterial Toxins / Q000378:metabolism*; D001665:Binding Sites; D003062:Codon; D009711:Nucleotides / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*
D001427:Bacterial Toxins; D003062:Codon; D009711:Nucleotides; D012333:RNA, Messenger
RNases; protein synthesis; ribosome; stringent response; toxin–antitoxin systems