Crystal structures of the Streptomyces coelicolor TetR-like protein ActR alone and in complex with actinorhodin or the actinorhodin biosynthetic precursor (S)-DNPA.
Actinorhodin, an antibiotic produced by Streptomyces coelicolor, is exported from the cell by the ActA efflux pump. actA is divergently transcribed from actR, which encodes a TetR-like transcriptional repressor. We showed previously that ActR represses transcription by binding to an operator from the actA/actR intergenic region. Importantly, actinorhodin itself or various actinorhodin biosynthetic intermediates can cause ActR to dissociate from its operator, leading to derepression. This suggests that ActR may mediate timely self-resistance to an endogenously produced antibiotic by responding to one of its biosynthetic precursors. Here, we report the structural basis for this precursor-mediated derepression with crystal structures of homodimeric ActR by itself and in complex with either actinorhodin or the actinorhodin biosynthetic intermediate (S)-DNPA [4-dihydro-9-hydroxy-1-methyl-10-oxo-3-H-naphtho-[2,3-c]-pyran-3-(S)-acetic acid]. The ligand-binding tunnel in each ActR monomer has a striking hydrophilic/hydrophobic/hydrophilic arrangement of surface residues that accommodate either one hexacyclic actinorhodin molecule or two back-to-back tricyclic (S)-DNPA molecules. Moreover, our work also reveals the strongest structural evidence to date that TetR-mediated antibiotic resistance may have been acquired from an antibiotic-producer organism.
Willems
A R
AR
Department of Biochemistry and Biomedical Sciences, McMaster University, 1200 Main Street West, Hamilton, Ontario, Canada.
Tahlan
K
K
Taguchi
T
T
Zhang
K
K
Lee
Z Z
ZZ
Ichinose
K
K
Junop
M S
MS
Nodwell
J R
JR
D000880:Anthraquinones / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009281:Naphthalenes / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011714:Pyrans / Q000378:metabolism*; D048372:Streptomyces coelicolor / Q000737:chemistry*; D000095622:Benzoisochromanequinones
D000880:Anthraquinones; D001426:Bacterial Proteins; D009281:Naphthalenes; D011714:Pyrans; C408422:4-dihydro-9-hydroxy-1-methyl-10-oxo-3-H-naphtho-(2,3-c)-pyran-3-acetic acid; C013390:actinorhodin; D000095622:Benzoisochromanequinones