Identification of ligands for RNA targets via structure-based virtual screening: HIV-1 TAR.
Binding of the Tat protein to TAR RNA is necessary for viral replication of HIV-1. We screened the Available Chemicals Directory (ACD) to identify ligands to bind to a TAR RNA structure using a four-step docking procedure: rigid docking first, followed by three steps of flexible docking using a pseudobrownian Monte Carlo minimization in torsion angle space with progressively more detailed conformational sampling on a progressively smaller list of top-ranking compounds. To validate the procedure, we successfully docked ligands for five RNA complexes of known structure. For ranking ligands according to binding avidity, an empirical binding free energy function was developed which accounts, in particular, for solvation, isomerization free energy, and changes in conformational entropy. System-specific parameters for the function were derived on a training set of RNA/ligand complexes with known structure and affinity. To validate the free energy function, we screened the entire ACD for ligands for an RNA aptamer which binds L-arginine tightly. The native ligand ranked 17 out of ca. 153,000 compounds screened, i.e., the procedure is able to filter out >99.98% of the database and still retain the native ligand. Screening of the ACD for TAR ligands yielded a high rank for all known TAR ligands contained in the ACD and suggested several other potential TAR ligands. Eight of the highest ranking compounds not previously known to be ligands were assayed for inhibition of the Tat-TAR interaction, and two exhibited a CD50 of ca. 1 microM.
Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA.
A V
AV
Filikov
V
V
Mohan
T A
TA
Vickers
R H
RH
Griffey
P D
PD
Cook
R A
RA
Abagyan
T L
TL
James
D001120:Arginine; D001483:Base Sequence; D001665:Binding Sites; D003198:Computer Simulation; D015195:Drug Design; D015696:Gene Products, tat / Q000737:chemistry / Q000378:metabolism; D016325:HIV Long Terminal Repeat; D015497:HIV-1 / Q000235:genetics / Q000502:physiology; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009010:Monte Carlo Method; D009690:Nucleic Acid Conformation; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics; D015203:Reproducibility of Results; D014779:Virus Replication; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D008024:Ligands; D012367:RNA, Viral; D054322:tat Gene Products, Human Immunodeficiency Virus; D001120:Arginine