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Matrix protein 2



Influenza A virus (strain A/Swine/Ontario/2/1981 H1N1)
Reviewed-Annotation score: Annotation score: 4 out of 5-Protein inferred from homologyi


Forms a proton-selective ion channel that is necessary for the efficient release of the viral genome during virus entry. After attaching to the cell surface, the virion enters the cell by endocytosis. Acidification of the endosome triggers M2 ion channel activity. The influx of protons into virion interior is believed to disrupt interactions between the viral ribonucleoprotein (RNP), matrix protein 1 (M1), and lipid bilayers, thereby freeing the viral genome from interaction with viral proteins and enabling RNA segments to migrate to the host cell nucleus, where influenza virus RNA transcription and replication occur. Also plays a role in viral proteins secretory pathway. Elevates the intravesicular pH of normally acidic compartments, such as trans-Golgi network, preventing newly formed hemagglutinin from premature switching to the fusion-active conformation (By similarity).By similarity

Enzyme regulationi

The M2 protein from most influenza A strains is inhibited by amantadine and rimantadine, resulting in viral uncoating incapacity. Emergence of amantadine-resistant variants is usually rapid.


Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Sitei37 – 371Essential for channel activity, possibly by being protonated during channel activation, and by forming the channel gate and the selective filterBy similarity
Sitei41 – 411Seems to be involved in pH gatingBy similarity

GO - Molecular functioni

  1. hydrogen ion transmembrane transporter activity Source: InterPro
  2. ion channel activity Source: UniProtKB-KW

GO - Biological processi

  1. pore formation by virus in membrane of host cell Source: UniProtKB-KW
  2. protein oligomerization Source: UniProtKB-KW
  3. suppression by virus of host autophagy Source: UniProtKB-KW
Complete GO annotation...

Keywords - Molecular functioni

Ion channel, Viral ion channel

Keywords - Biological processi

Host-virus interaction, Hydrogen ion transport, Inhibition of host autophagy by virus, Ion transport, Transport

Names & Taxonomyi

Protein namesi
Recommended name:
Matrix protein 2
Alternative name(s):
Proton channel protein M2
Gene namesi
OrganismiInfluenza A virus (strain A/Swine/Ontario/2/1981 H1N1)
Taxonomic identifieri384501 [NCBI]
Taxonomic lineageiVirusesssRNA negative-strand virusesOrthomyxoviridaeInfluenzavirus A
Virus hostiAves [TaxID: 8782]
Homo sapiens (Human) [TaxID: 9606]
Sus scrofa (Pig) [TaxID: 9823]

Subcellular locationi

  1. Virion membrane By similarity
  2. Host apical cell membrane By similarity; Single-pass type III membrane protein By similarity

  3. Note: Abundantly expressed at the apical plasma membrane in infected polarized epithelial cells, in close proximity to budding and assembled virions. Minor component of virions (only 16-20 molecules/virion) (By similarity).By similarity


Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Topological domaini1 – 2222Virion surfaceSequence AnalysisAdd
Transmembranei23 – 4321HelicalSequence AnalysisAdd
Topological domaini44 – 9754IntravirionSequence AnalysisAdd

GO - Cellular componenti

  1. host cell plasma membrane Source: UniProtKB-SubCell
  2. integral component of membrane Source: UniProtKB-KW
  3. integral to membrane of host cell Source: UniProtKB-KW
  4. virion membrane Source: UniProtKB-SubCell
Complete GO annotation...

Keywords - Cellular componenti

Host cell membrane, Host membrane, Membrane, Virion

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 9797Matrix protein 2PRO_0000326376Add

Amino acid modifications

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Disulfide bondi17 – 17Interchain (with C-17)By similarity
Disulfide bondi19 – 19Interchain (with C-19)By similarity
Lipidationi50 – 501S-palmitoyl cysteine; by hostBy similarity
Modified residuei64 – 641Phosphoserine; by hostBy similarity

Keywords - PTMi

Disulfide bond, Lipoprotein, Palmitate, Phosphoprotein


Subunit structurei

Homotetramer; composed of two disulfide-linked dimers held together by non-covalent interactions. May interact with matrix protein 1 (By similarity).By similarity

Family & Domainsi


Cytoplasmic tail plays an important role in virion assembly and morphogenesis.By similarity

Sequence similaritiesi

Keywords - Domaini

Signal-anchor, Transmembrane, Transmembrane helix

Family and domain databases

InterProiIPR002089. Flu_M2.
[Graphical view]
PfamiPF00599. Flu_M2. 1 hit.
[Graphical view]
ProDomiPD001031. Flu_M2. 1 hit.
[Graphical view] [Entries sharing at least one domain]

Sequences (2)i

Sequence statusi: Complete.

This entry describes 2 isoformsi produced by alternative splicing. AlignAdd to basket

Note: Only the first 9 residues are shared by the 2 isoforms.

Isoform M2 (identifier: Q67203-1) [UniParc]FASTAAdd to basket

This isoform has been chosen as the 'canonical' sequence. All positional information in this entry refers to it. This is also the sequence that appears in the downloadable versions of the entry.

« Hide

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60 70 80 90
Mass (Da):11,186
Last modified:November 1, 1996 - v1
Isoform M1 (identifier: Q67204-1) [UniParc]FASTAAdd to basket

The sequence of this isoform can be found in the external entry Q67204.
Isoforms of the same protein are often annotated in two different entries if their sequences differ significantly.
Mass (Da):27,882

Sequence databases

Select the link destinations:
Links Updated
M63520 Genomic RNA. Translation: AAA43337.1.

Keywords - Coding sequence diversityi

Alternative splicing


Sequence databases

Select the link destinations:
Links Updated
M63520 Genomic RNA. Translation: AAA43337.1.

3D structure databases


Protocols and materials databases

Structural Biology KnowledgebaseSearch...

Family and domain databases

InterProiIPR002089. Flu_M2.
[Graphical view]
PfamiPF00599. Flu_M2. 1 hit.
[Graphical view]
ProDomiPD001031. Flu_M2. 1 hit.
[Graphical view] [Entries sharing at least one domain]


  1. "Evolutionary analysis of the influenza A virus M gene with comparison of the M1 and M2 proteins."
    Ito T., Gorman O.T., Kawaoka Y., Bean W.J., Webster R.G.
    J. Virol. 65:5491-5498(1991) [PubMed] [Europe PMC] [Abstract]

Entry informationi

Entry nameiM2_I81A4
AccessioniPrimary (citable) accession number: Q67203
Entry historyi
Integrated into UniProtKB/Swiss-Prot: March 18, 2008
Last sequence update: November 1, 1996
Last modified: January 7, 2015
This is version 57 of the entry and version 1 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programViral Protein Annotation Program



When the channel is activated, one or more imidazole moities of His-37 probably become bi-protonated.


  1. SIMILARITY comments
    Index of protein domains and families

External Data

Dasty 3

Similar proteinsi

Links to similar proteins from the UniProt Reference Clusters (UniRef) at 100%, 90% and 50% sequence identity:
100%UniRef100 combines identical sequences and sub-fragments with 11 or more residues from any organism into Uniref entry.
90%UniRef90 is built by clustering UniRef100 sequences that have at least 90% sequence identity to, and 80% overlap with, the longest sequence (a.k.a seed sequence).
50%UniRef50 is built by clustering UniRef90 seed sequences that have at least 50% sequence identity to, and 80% overlap with, the longest sequence in the cluster.