PDBsum entry 5k5m

Hydrolase

PDB id: 5k5m

Contents

Protein chain

563 a.a.

Ligands

68T

MES

Metals

_ZN ×2

Waters ×429

References listed in PDB file

Key reference

• Title: Potent allosteric dengue virus ns5 polymerase inhibitors: mechanism of action and resistance profiling.
• Authors: S.P.Lim, C.G.Noble, C.C.Seh, T.S.Soh, A.El sahili, G.K.Chan, J.Lescar, R.Arora, T.Benson, S.Nilar, U.Manjunatha, K.F.Wan, H.Dong, X.Xie, P.Y.Shi, F.Yokokawa.
• Ref.: Plos Pathog, 2016, 12, e1005737. [DOI no: 10.1371/journal.ppat.1005737]
• PubMed id: 27500641

Abstract

Flaviviruses comprise major emerging pathogens such as dengue virus (DENV) or Zika virus (ZIKV). The flavivirus RNA genome is replicated by the RNA-dependent-RNA polymerase (RdRp) domain of non-structural protein 5 (NS5). This essential enzymatic activity renders the RdRp attractive for antiviral therapy. NS5 synthesizes viral RNA via a "de novo" initiation mechanism. Crystal structures of the flavivirus RdRp revealed a "closed" conformation reminiscent of a pre-initiation state, with a well ordered priming loop that extrudes from the thumb subdomain into the dsRNA exit tunnel, close to the "GDD" active site. To-date, no allosteric pockets have been identified for the RdRp, and compound screening campaigns did not yield suitable drug candidates. Using fragment-based screening via X-ray crystallography, we found a fragment that bound to a pocket of the apo-DENV RdRp close to its active site (termed "N pocket"). Structure-guided improvements yielded DENV pan-serotype inhibitors of the RdRp de novo initiation activity with nano-molar potency that also impeded elongation activity at micro-molar concentrations. Inhibitors exhibited mixed inhibition kinetics with respect to competition with the RNA or GTP substrate. The best compounds have EC50 values of 1-2 μM against all four DENV serotypes in cell culture assays. Genome-sequencing of compound-resistant DENV replicons, identified amino acid changes that mapped to the N pocket. Since inhibitors bind at the thumb/palm interface of the RdRp, this class of compounds is proposed to hinder RdRp conformational changes during its transition from initiation to elongation. This is the first report of a class of pan-serotype and cell-active DENV RdRp inhibitors. Given the evolutionary conservation of residues lining the N pocket, these molecules offer insights to treat other serious conditions caused by flaviviruses.