9X91 | pdb_00009x91

Solution structure of anti-CRISPR AcrIIA8

• PDB DOI: https://doi.org/10.2210/pdb9X91/pdb

• Classification: VIRAL PROTEIN
• Organism(s): metagenome
• Expression System: Escherichia coli
• Mutation(s): No 


• Deposited: 2025-10-20 Released: 2026-06-24 
• Deposition Author(s): Kim, I., An, S.Y., Hong, S.H., Suh, J.Y.
• Funding Organization(s): National Research Foundation (NRF, Korea)

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Experimental Data Snapshot

• Method: SOLUTION NMR
• Conformers Calculated: 2000 
• Conformers Submitted: 20 
• Selection Criteria: structures with acceptable covalent geometry 

Literature

AcrIIA8 is a putative phage structural protein of the HTJ2 family that does not inhibit Streptococcus pyogenes Cas9.

An, S.Y., Kim, I., Hong, S.H., Kim, E.H., Suh, J.Y.

(2026) Protein Sci 35: e70651-e70651

• PubMed: 42223080 
• DOI: https://doi.org/10.1002/pro.70651
• Primary Citation Related Structures: 
  9X91


• PubMed Abstract: 
  

  Anti-CRISPR (Acr) proteins are phage-encoded anti-defense factors that suppress CRISPR-Cas immunity in bacteria. AcrIIA8 was previously identified as an inhibitor of Streptococcus pyogenes Cas9 (SpyCas9) through functional assays of metagenomic libraries. Here, we report that AcrIIA8 does not inhibit SpyCas9 in biochemical assays under a range of buffer conditions and temperatures. The solution structure and dynamics of AcrIIA8 reveal a six-stranded β-barrel fold with flexible β1-β2 and β2-β3 loops, characteristic of phage virion-assembly proteins. In addition, genomic context analysis places AcrIIA8 and its homologs within conserved prophage morphogenetic regions at the position expected for type II head-tail joining (HTJ2) proteins. We further detected no interaction between AcrIIA8 and SpyCas9 in NMR titration experiments, suggesting that they do not specifically associate. Taken together, these findings argue against assigning AcrIIA8 as a SpyCas9 inhibitor and instead support its annotation as a putative phage structural protein of the HTJ2 family.

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Organizational Affiliation: 
• Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Korea.
Advanced Analysis Data Center, Korea Institute of Science and Technology, Seoul, Korea.
Biopharmaceutical Research Center, Korea Basic Science Institute, Ochang, Korea.
Department of Agricultural Biotechnology, Seoul National University, Seoul, Korea.

Biological Assembly 1  

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Monomer - A1 

Biological assembly 1 assigned by authors and generated by (software)

Biological Assembly Evidence: gel filtration

Macromolecule Content 

• Total Structure Weight: 12.02 kDa 
• Atom Count: 843 
• Modeled Residue Count: 105 
• Deposited Residue Count: 105 
• Unique protein chains: 1

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Inhibitor of Type II CRISPR-Cas system	A	105	metagenome	Mutation(s): 0  Gene Names: acrIIA8
UniProt
Find proteins for A0A447EB47 (metagenome) Explore A0A447EB47  Go to UniProtKB:  A0A447EB47

Experimental Data & Validation

Experimental Data

• Method: SOLUTION NMR
• Conformers Calculated: 2000 
• Conformers Submitted: 20 
• Selection Criteria: structures with acceptable covalent geometry 

Structure Validation

Entry History 

& Funding Information

Deposition Data

• Released Date: 2026-06-24 
Deposition Author(s): Kim, I., An, S.Y., Hong, S.H., Suh, J.Y.

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Funding Organization	Location	Grant Number
National Research Foundation (NRF, Korea)	Korea, Republic Of	2021R1A2C1003917
National Research Foundation (NRF, Korea)	Korea, Republic Of	RS-2023-00207820

Revision History  

• Version 1.0: 2026-06-24
  Type: Initial release