9T0R | pdb_00009t0r

Crystal structure of SARS-CoV-2 Mpro in complex with GK729

• PDB DOI: https://doi.org/10.2210/pdb9T0R/pdb

• Classification: VIRAL PROTEIN
• Organism(s): Severe acute respiratory syndrome coronavirus 2
• Expression System: Escherichia coli
• Mutation(s): No 


• Deposited: 2025-10-20 Released: 2026-08-05 
• Deposition Author(s): El Kilani, H., Hilgenfeld, R.
• Funding Organization(s): European Commission

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 1.55 Å
• R-Value Free: 
  0.245 (Depositor), 0.263 (DCC) 
• R-Value Work: 
  0.216 (Depositor), 0.234 (DCC) 

Starting Model: experimental

Literature

Thiazolyl 4-carboxylate ketone as a new warhead for a highly potent SARS-CoV-2 main protease inhibitor.

Theodoropoulou, M.A., El Kilani, H., Mantzourani, C., Jochmans, D., Neyts, J., Zhang, K., Roske, J., Kokotou, M.G., Hilgenfeld, R., Kokotos, G.

(2026) Eur J Med Chem 303: 118436-118436

• PubMed: 41344111 
• DOI: https://doi.org/10.1016/j.ejmech.2025.118436
• Primary Citation Related Structures: 
  9H4B, 9T0R


• PubMed Abstract: 
  

  The SARS-CoV-2 main protease (M ^pro ), an enzyme essential for viral replication and lacking a human homologue, has emerged as a highly attractive target for the development of novel antiviral agents. Although several M ^pro inhibitors have been developed - some receiving regulatory approval - their use is sometimes limited by drug-drug interactions. In this study, we designed and synthesized peptidomimetic SARS-CoV-2 M ^pro inhibitors incorporating a novel thiazolyl 4-carboxylate ketone warhead, previously employed by our group in the development of cytosolic phospholipase A ₂ inhibitors. The synthesized compounds were evaluated for their in vitro inhibitory potency against SARS-CoV-2 M ^pro , and a highly potent M ^pro inhibitor (GK730) was identified (IC ₅₀ 5.75 nM). The melting temperature of the M ^pro -GK730 complex revealed high stability, consistent with the high inhibitory potency. The X-ray crystal structures of inhibitors GK729 and GK730 bound to M ^pro were determined, providing insights into the binding interactions and mechanism of action. Studies on the host cell proteases cathepsin B and L showed that GK730 did not inhibit cathepsin B, while exhibited weak inhibition of cathepsin L. Furthermore, GK730 demonstrated an EC ₅₀ value of 5.70 μM against a wild-type SARS-CoV-2 strain in Vero E6 cells and minimal cytotoxicity (CC ₅₀ value greater than 100 μM).

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Organizational Affiliation: 
• Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece; Center of Excellence for Drug Design and Discovery, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece. Electronic address: [e-mail].
Institute of Molecular Medicine, University of Lübeck, Ratzeburger Allee 160, 23562, Lübeck, Germany. Electronic address: [e-mail].
Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece; Center of Excellence for Drug Design and Discovery, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece. Electronic address: [e-mail].
Virology, Antiviral Drug & Vaccine Research Group, Department of Microbiology, Immunology and Transplantation, Rega Institute, KU Leuven, Leuven, Belgium. Electronic address: [e-mail].
Virology, Antiviral Drug & Vaccine Research Group, Department of Microbiology, Immunology and Transplantation, Rega Institute, KU Leuven, Leuven, Belgium. Electronic address: [e-mail].
Institute of Molecular Medicine, University of Lübeck, Ratzeburger Allee 160, 23562, Lübeck, Germany. Electronic address: [e-mail].
Institute of Molecular Medicine, University of Lübeck, Ratzeburger Allee 160, 23562, Lübeck, Germany. Electronic address: [e-mail].
Laboratory of Chemistry, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 11855, Athens, Greece. Electronic address: [e-mail].
Institute of Molecular Medicine, University of Lübeck, Ratzeburger Allee 160, 23562, Lübeck, Germany. Electronic address: [e-mail].
Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece; Center of Excellence for Drug Design and Discovery, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Athens, Greece. Electronic address: [e-mail].

Biological Assembly 1  

Global Symmetry: Cyclic - C2  (Explore in 3D)
Global Stoichiometry: Homo 2-mer - A2 

Biological assembly 1 assigned by authors.

Biological Assembly Evidence: native gel electrophoresis

Biological Assembly 2  

Global Symmetry: Cyclic - C2  (Explore in 3D)
Global Stoichiometry: Homo 2-mer - A2 

Biological assembly 2 assigned by authors.

Macromolecule Content 

• Total Structure Weight: 137.48 kDa 
• Atom Count: 10,245 
• Modeled Residue Count: 1,219 
• Deposited Residue Count: 1,224 
• Unique protein chains: 1

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
3C-like proteinase nsp5	A, B, C, D	306	Severe acute respiratory syndrome coronavirus 2	Mutation(s): 0  EC: 3.4.22.69
UniProt
Find proteins for P0DTC1 (Severe acute respiratory syndrome coronavirus 2) Explore P0DTC1  Go to UniProtKB:  P0DTC1

Small Molecules

Ligands 1 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
A1JSW (Subject of Investigation/LOI)	E [auth A], F [auth B], G [auth C], H [auth D]	(phenylmethyl) ~{N}-[(2~{S})-1-[[(1~{S},2~{S})-1-[4-(1-methoxyethenyl)-1,3-thiazol-2-yl]-1-oxidanyl-3-[(3~{S})-2-oxidanylidenepyrrolidin-3-yl]propan-2-yl]amino]-4-methyl-1-oxidanylidene-pentan-2-yl]carbamate C27 H36 N4 O6 S LWGFATQVPSGUTC-FKEBYFGASA-N

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 1.55 Å
• R-Value Free:  0.245 (Depositor), 0.263 (DCC) 
• R-Value Work:  0.216 (Depositor), 0.234 (DCC) 

Space Group: P 1 2₁ 1

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 67.749	α = 90
b = 102.788	β = 101.063
c = 104.697	γ = 90

Software Package:

Software Name	Purpose
REFMAC	refinement
XDS	data reduction
Aimless	data scaling
MOLREP	phasing

Structure Validation

Entry History 

& Funding Information

Deposition Data

• Released Date: 2026-08-05 
Deposition Author(s): El Kilani, H., Hilgenfeld, R.

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Funding Organization	Location	Grant Number
European Commission	European Union	--

Revision History  

• Version 1.0: 2026-08-05
  Type: Initial release