Structure of the bacteriophage T4 capsid assembly protease, gp21.

  • Classification: HYDROLASE
  • Organism(s): Tequatrovirus T4
  • Expression System: Escherichia coli
  • Mutation(s): Yes 

  • Deposited: 2016-04-13 Released: 2016-12-07 
  • Deposition Author(s): Fokine, A., Rossmann, M.G.
  • Funding Organization(s): National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)

Experimental Data Snapshot

  • Resolution: 1.94 Å
  • R-Value Free: 0.205 
  • R-Value Work: 0.172 
  • R-Value Observed: 0.173 

wwPDB Validation   3D Report Full Report

This is version 1.3 of the entry. See complete history


Common Evolutionary Origin of Procapsid Proteases, Phage Tail Tubes, and Tubes of Bacterial Type VI Secretion Systems.

Fokine, A.Rossmann, M.G.

(2016) Structure 24: 1928-1935

  • DOI: https://doi.org/10.1016/j.str.2016.08.013
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Many large viruses, including tailed dsDNA bacteriophages and herpesviruses, assemble their capsids via formation of precursors, called procapsids or proheads. The prohead has an internal core, made of scaffolding proteins, and an outer shell, formed by the major capsid protein. The prohead usually contains a protease, which is activated during capsid maturation to destroy the inner core and liberate space for the genome. Here, we report a 2.0 Å resolution structure of the pentameric procapsid protease of bacteriophage T4, gene product (gp)21. The structure corresponds to the enzyme's pre-active state in which its N-terminal region blocks the catalytic center, demonstrating that the activation mechanism involves self-cleavage of nine N-terminal residues. We describe similarities and differences between T4 gp21 and related herpesvirus proteases. We found that gp21 and the herpesvirus proteases have similarity with proteins forming the tubes of phage tails and bacterial type VI secretion systems, suggesting their common evolutionary origin.

  • Organizational Affiliation

    Department of Biological Sciences, Hockmeyer Hall of Structural Biology, Purdue University, 240 South Martin Jischke Drive, West Lafayette, IN 47907, USA. Electronic address: afokine@purdue.edu.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Prohead core protein protease
A, B, C, D, E
231Tequatrovirus T4Mutation(s): 3 
Gene Names: 21
EC: 3.4.99
Find proteins for P06807 (Enterobacteria phage T4)
Explore P06807 
Go to UniProtKB:  P06807
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP06807
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.94 Å
  • R-Value Free: 0.205 
  • R-Value Work: 0.172 
  • R-Value Observed: 0.173 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 41.745α = 90
b = 124.041β = 89.96
c = 88.959γ = 90
Software Package:
Software NamePurpose
HKL-2000data reduction
HKL-2000data scaling

Structure Validation

View Full Validation Report

Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)United StatesAI081726

Revision History  (Full details and data files)

  • Version 1.0: 2016-12-07
    Type: Initial release
  • Version 1.1: 2017-09-20
    Changes: Author supporting evidence, Database references
  • Version 1.2: 2019-12-11
    Changes: Author supporting evidence
  • Version 1.3: 2024-03-06
    Changes: Data collection, Database references