Crystal Structure of the Vapbc-15 Complex from Mycobacterium Tuberculosis Reveals a Two-Metal Ion Dependent Pin-Domain Ribonuclease And a Variable Mode of Toxin-Antitoxin Assembly.Das, U., Pogenberg, V., Subhramanyam, U.K.T., Wilmanns, M., Gourinath, S., Srinivasan, A.
(2014) J Struct Biol 188: 249
- PubMed: 25450593
- DOI: https://doi.org/10.1016/j.jsb.2014.10.002
- Primary Citation of Related Structures:
- PubMed Abstract:
Although PIN (PilT N-terminal)-domain proteins are known to have ribonuclease activity, their specific mechanism of action remains unknown. VapCs form a family of ribonucleases that possess a PIN-domain assembly and are known as toxins. The activities of VapCs are impaired by VapB antitoxins. Here we present the crystal structure of the VapBC-15 toxin-antitoxin complex from Mycobacterium tuberculosis determined to 2.1Å resolution. The VapB-15 and VapC-15 components assemble into one heterotetramer (VapB2C2) and two heterotrimers (VapBC2) in each asymmetric unit of the crystal. The active site of VapC-15 toxin consists of a cluster of acidic amino acid residues and two divalent metal ions, forming a well organised ribonuclease active site. The distribution of the catalytic-site residues of the VapC-15 toxin is similar to that of T4 RNase H and of Methanococcus jannaschii FEN-1, providing strong evidence that these three proteins share a similar mechanism of activity. The presence of both VapB2C2 and VapBC2 emphasizes the fact that the same antitoxin can bind the toxin in 1:1 and 1:2 ratios. The crystal structure determination of the VapBC-15 complex reveals for the first time a PIN-domain ribonuclease protein that shows two metal ions at the active site and a variable mode of toxin-antitoxin assembly. The structure further shows that VapB-15 antitoxin binds to the same groove meant for the binding of putative substrate (RNA), resulting in the inhibition of VapC-15's toxicity.
Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India.