Database accession: MF3140001
Name: Bacteriophage T4 fibritin
PDB ID: 1aa0
Experimental method: X-ray (2.20 Å)
Assembly: homotrimer
Source organism: Enterobacteria phage T4
Primer publication of the structure:
Tao Y, Strelkov SV, Mesyanzhinov VV, Rossmann MG
Structure of bacteriophage T4 fibritin: a segmented coiled coil and the role of the C-terminal domain.
(1997) Structure 5: 789-98
PMID: 9261070
Abstract:
CONCLUSIONS: The residues within the C-terminal domain make extensive hydrophobic and some polar intersubunit interactions. This is consistent with the C-terminal domain being important for the correct assembly of fibritin, as shown earlier by mutational studies. Tight interactions between the C-terminal residues of adjacent subunits counteract the latent instability that is suggested by the structural properties of the coiled-coil segments. Trimerization is likely to begin with the formation of the C-terminal domain which subsequently initiates the assembly of the coiled coil. The interplay between the stabilizing effect of the C-terminal domain and the labile coiled-coil domain may be essential for the fibritin function and for the correct functioning of many other alpha-fibrous proteins.
RESULTS: The three-dimensional structure of fibritin E, a deletion mutant of wild-type fibritin, was determined to 2.2 A resolution by X-ray crystallography. Three identical subunits of 119 amino acid residues form a trimeric parallel coiled-coil domain and a small globular C-terminal domain about a crystallographic threefold axis. The coiled-coil domain is divided into three segments that are separated by insertion loops. The C-terminal domain, which consists of 30 residues from each subunit, contains a beta-propeller-like structure with a hydrophobic interior.
BACKGROUND: Oligomeric coiled-coil motifs are found in numerous protein structures; among them is fibritin, a structural protein of bacteriophage T4, which belongs to a class of chaperones that catalyze a specific phage-assembly process. Fibritin promotes the assembly of the long tail fibers and their subsequent attachment to the tail baseplate; it is also a sensing device that controls the retraction of the long tail fibers in adverse environments and, thus, prevents infection. The structure of fibritin had been predicted from sequence and biochemical analyses to be mainly a triple-helical coiled coil. The determination of its structure at atomic resolution was expected to give insights into the assembly process and biological function of fibritin, and the properties of modified coiled-coil structures in general.
Annotations from the GeneOntology database. Only terms that fit at least two of the interacting proteins are shown.Molecular function: not assigned
Biological process: not assigned
Cellular component:
virion The complete fully infectious extracellular virus particle.
Structural annotations of the participating protein chains.Entry contents: 3 distinct polypeptide molecules
Chains: A, B, C
Notes: Chains B and C were generated from chain A using the biomatrices described in the original PDB file.
Number of unique protein segments: 1
Name: Fibritin
Source organism: Enterobacteria phage T4
Length: 113 residues
Sequence:Sequence according to PDB SEQRESVSGLNNAVQNLQVEIGNNSAGIKGQVVALNTLVNGTNPNGSTVEERGLTNSIKANETNIASVTQEVNTAKGNISSLQGDVQALQEAGYIPEAPRDGQAYVRKDGEWVLLSTFL
UniProtKB AC: P10104 (positions: 372-484) Coverage: 23.2%
UniRef90 AC: UniRef90_P10104 (positions: 372-484)
Name: Fibritin
Source organism: Enterobacteria phage T4
Length: 113 residues
Sequence:Sequence according to PDB SEQRESVSGLNNAVQNLQVEIGNNSAGIKGQVVALNTLVNGTNPNGSTVEERGLTNSIKANETNIASVTQEVNTAKGNISSLQGDVQALQEAGYIPEAPRDGQAYVRKDGEWVLLSTFL
UniProtKB AC: P10104 (positions: 372-484) Coverage: 23.2%
UniRef90 AC: UniRef90_P10104 (positions: 372-484)
Name: Fibritin
Source organism: Enterobacteria phage T4
Length: 113 residues
Sequence:Sequence according to PDB SEQRESVSGLNNAVQNLQVEIGNNSAGIKGQVVALNTLVNGTNPNGSTVEERGLTNSIKANETNIASVTQEVNTAKGNISSLQGDVQALQEAGYIPEAPRDGQAYVRKDGEWVLLSTFL
UniProtKB AC: P10104 (positions: 372-484) Coverage: 23.2%
UniRef90 AC: UniRef90_P10104 (positions: 372-484)
Evidence demonstrating that the participating proteins are unstructured prior to the interaction and their folding is coupled to binding. Complex evidence:
The foldon domain folds into a trimeric beta-propeller structure and undergoes a two-state unfolding transition from folded trimer to unfolded monomers (PMID: 15033360). The other subunits in the structure are bound via coiled coil interactions (PMID: 9261070). Coiled coils are highly versatile folding units (PMID: 11166216), where the formation of the structure and the interaction between subunits is almost ubiquitously linked. This cooperative nature of binding and folding that results in a two-step process has been demonstrated for coiled coils with varying oligomeric state from dimers (PMID: 9811815) and trimers (PMID: 10933510) up to heptamers (PMID: 17030805). While the interaction and folding are linked, in certain cases there can be significant residual structure before association (PMID: 8401212). However, these residual structural elements usually encompass 1-2 turns of helices that serve as a 'nucleation site' driving interaction and helix formation (zipping up) (PMID: 17438295), thus even in these cases monomeric coiled coil subunits cannot be considered to have a stable structure.
Structures from the PDB that contain the same number of proteins, and the proteins from the two structures show a sufficient degree of pairwise similarity, i.e. they belong to the same UniRef90 cluster (the full proteins exhibit at least 90% sequence identity) and convey roughly the same region to their respective interactions (the two regions from the two proteins share a minimum of 70% overlap). Download our modified structure (.pdb)
