SUPERFAMILY 1.75 HMM library and genome assignments server

Outer capsid protein sigma 3 superfamily

SCOP classification
Root:   SCOP hierarchy in SUPERFAMILY [ 0] (11)
Class:   Alpha and beta proteins (a+b) [ 53931] (376)
Fold:   Outer capsid protein sigma 3 [ 64464]
Superfamily:   Outer capsid protein sigma 3 [ 64465]
Families:   Outer capsid protein sigma 3 [ 64466]

Superfamily statistics
Genomes (3) Uniprot 2013_05 PDB chains (SCOP 1.75)
Domains 3 176 2
Proteins 3 176 2

Functional annotation
General category Other
Detailed category Viral proteins

Function annotation of SCOP domain superfamilies

InterPro annotation
Cross references IPR000153 SSF64465 Protein matches

Reoviruses are double-stranded RNA viruses that lack a membrane envelope. Their capsid is organised in two concentric icosahedral layers: an inner core and an outer capsid layer. The sigma1 protein is found in the outer capsid, and the sigma2 protein is found in the core. There are four other kinds of protein (besides sigma2) in the core, termed lambda 1-3, mu2. Interactions between sigma2 and lambda 1 and lambda 3 are thought to initiate core formation, followed by mu2 and lambda2 [PubMed9971813].

Sigma1 is a trimeric protein, and is positioned at the 12 vertices of the icosahedral outer capsid layer. Its N-terminal fibrous tail, arranged as a triple coiled coil, anchors it in the virion, and a C-terminal globular head interacts with the cellular receptor [PubMed11438552]. These two parts form by separate trimerization events. The N-terminal fibrous tail forms on the polysome, without the involvement of ATP or chaperones. The post- translational assembly of the C-terminal globular head involves the chaperone activity of Hsp90, which is associated with phosphorylation of Hsp90 during the process [PubMed11438552]. Sigma1 protein acts as a cell attachment protein, and determines viral virulence, pathways of spread, and tropism. Junctional adhesion molecule has been identified as a receptor for sigma1 [PubMed11239401]. In type 3 reoviruses, a small region, predicted to form a beta sheet, in the N-terminal tail was found to bind target cell surface sialic acid (i.e. sialic acid acts as a co-receptor) and promote apoptosis [PubMed11287552]. The sigma1 protein also binds to the lambda2 core protein [PubMed9311901].

InterPro database

PDBeMotif information about ligands, sequence and structure motifs
Cross references PDB entries
Ligand binding statistics
Nucleic-acid binding statistics
Occurrence of secondary structure elements
Occurrence of small 3D structural motifs

PDBeMotif resource

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Internal database links

Browse genome assignments for this superfamily. The SUPERFAMILY hidden Markov model library has been used to carry out SCOP domain assignments to all genomes at the superfamily level.

Alignments of sequences to 1 models in this superfamily are available by clicking on the 'Alignments' icon above. PDB sequences less than 40% identical are shown by default, but any other sequence(s) may be aligned. Select PDB sequences, genome sequences, or paste in or upload your own sequences.

Browse and view proteins in genomes which have different domain combinations including a Outer capsid protein sigma 3 domain.

Examine the distribution of domain superfamilies, or families, across the major taxonomic kingdoms or genomes within a kingdom. This gives an immediate impression of how superfamilies, or families, are restricted to certain kingdoms of life.

Explore domain occurrence network where nodes represent genomes and edges are domain architectures (shared between genomes) containing the superfamily of interest.

There are 1 hidden Markov models representing the Outer capsid protein sigma 3 superfamily. Information on how the models are built, and plots showing hydrophobicity, match emmission probabilities and insertion/deletion probabilities can be inspected.

Jump to [ Top of page · SCOP classification · InterPro annotation · PDBeMotif links · Functional annotation · Internal database links ]