9EC2 image
Entry Detail
PDB ID:
9EC2
Keywords:
Title:
Crystal structure of SAMHD1 dimer bound to an inhibitor obtained from high-throughput chemical tethering to the guanine antiviral acyclovir
Biological Source:
Source Organism:
Host Organism:
PDB Version:
Deposition Date:
2024-11-13
Release Date:
2025-03-12
Method Details:
Experimental Method:
Resolution:
2.72 Å
R-Value Free:
0.23
R-Value Work:
0.18
R-Value Observed:
0.19
Space Group:
P 1
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Deoxynucleoside triphosphate triphosphohydrolase SAMHD1
Chain IDs:A, B, C, D
Chain Length:516
Number of Molecules:4
Biological Source:Homo sapiens
Primary Citation

Abstact

Sterile alpha motif histidine-aspartate domain protein 1 (SAMHD1) is an enzyme with diverse activities. Its dNTPase activity degrades all canonical dNTPs and many anticancer nucleoside drugs, while its single-stranded nucleic acid binding activity promotes DNA repair and RNA homeostasis in cells. These functions require guanine nucleotide binding to a specific allosteric site (A1) on the enzyme. We previously described how the activities of SAMHD1 could be inhibited in vitro with fragment-based inhibitor design, using dGMP as a targeting fragment for the A1 site. However, these dGMP-tethered inhibitors had poor cell permeability due to the charged guanine monophosphate group. Here, we describe a new approach where the amino form of the guanine acyclic nucleoside acyclovir (NH2-ACV) is used as the targeting fragment, allowing facile coupling to activated carboxylic acids (R-COOH), either directly or using linkers. This approach generates a neutral amide instead of charged monophosphate attachment points. High-throughput screening of a ∼375 compound carboxylic acid library identified two compounds (8, 11) with similar micromolar affinities for SAMHD1. Compound 11 was obtained by direct coupling to NH2-ACV, while compound 8 used a five-carbon linker. Both inhibitors had the same dibromonaphthol component from the carboxylic acid library screen. A crystal structure of a complex between SAMHD1 and 8, combined with computational models of bound 11, suggest how the dibromonaphthol promotes binding. The findings establish that guanine-based inhibitors targeting the A1 site do not require nucleotide or cyclic nucleoside structural elements. This guanine site targeting strategy is highly amenable to further chemical optimization.

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