Disease relevance of CM2

• It was found that the colinear mRNA derived from influenza C virus RNA segment 6 serves as the mRNA for CM2 [1].
• These results, altogether, suggest that CM2 is an integral membrane protein with biochemical properties similar to those of influenza A virus M2 and influenza B virus NB proteins [2].
• Furthermore, evidence that a small amount of CM2 is incorporated into progeny virus particles was obtained by Western blot analysis [2].
• The CM2 protein of influenza C virus is an oligomeric integral membrane glycoprotein structurally analogous to influenza A virus M2 and influenza B virus NB proteins [3].

High impact information on CM2

• Influenza C virus CM2 integral membrane glycoprotein is produced from a polypeptide precursor by cleavage of an internal signal sequence [1].
• Alteration of the predicted signal peptidase cleavage site by mutagenesis blocked generation of CM2 [1].
• Furthermore, CM2 translation does not depend on any of the three in-frame methionine residues located at the beginning of CM2 ORF [1].
• When the same experiment was done with the transcript of the mutated M gene in which the second recognition motif was removed, synthesis of CM2 could not be seen, even in the presence of microsomes [4].
• From these results, we conclude that cleavage of P42 by signal peptidase after Ala residue 259 produces CM2, composed of the C-terminal 115 amino acids, in addition to M1', composed of the N-terminal 259 amino acids [4].

Biological context of CM2

• CM2 mutants defective in acylation, phosphorylation or disulphide bond formation were all transported to the cell surface, suggesting that none of these modifications is required for proper oligomerization [5].
• This polypeptide, which has not been identified as yet, is predicted to contain the complete amino acid sequence of the matrix protein, M1, as well as that of a small integral membrane protein, CM2 [6].
• An antiserum raised to a C-terminal peptide in the CM2 open reading frame recognized the CM2 protein in influenza C virus-infected cells and after vac-T7 expression of the CM2 open reading frame [3].

Anatomical context of CM2

• Trypsin treatment of infected cell surfaces as well as of microsome vesicles from infected cells followed by immunoprecipitation with antiserum to the GST fusion protein containing the 56 C-terminal amino acid residues of CM2 suggested that this C-terminal domain is intracellular and exposed to the cytoplasms of microsomes [2].
• To examine the possibility that P42 is cleaved by signal peptidase after Ser residue 254 or Ala residue 259 to yield CM2, we constructed three mutated M gene cDNAs in which either or both of the two sequences were eliminated and tested their ability to synthesize CM2 in the transfected COS cells [4].
• Site-directed mutagenesis eliminated the single potential N-linked carbohydrate attachment site on CM2 and indicated that the protein has an NoutCin orientation in membranes [3].
• We also found that the anti-influenza A virus drug amantadine hydrochloride failed to attenuate the inward currents of CM2-expressing oocytes induced by hyperpolarization [7].

Associations of CM2 with chemical compounds

• When proteins solubilized in detergent were analysed on sucrose gradients, however, the mutant lacking cysteines 1, 6 and 20 sedimented as monomers, raising the possibility that disulphide bond formation, although not essential for proper oligomerization, may stabilize the CM2 multimer [5].
• The unglycosylated form of CM2 synthesized in the presence of tunicamycin was found to be highly phosphorylated [8].
• Phosphorylation of CM2 was also inhibited strongly, although not completely, by monensin treatment, suggesting that CM2 is phosphorylated predominantly after its movement from medial to trans Golgi cisternae [8].
• It was shown recently that CM2 in vitro forms a voltage-activated ion channel permeable to chloride ion (Hongo et al., Arch. Virol. 149, 35-50, 2004) [9].
• Labeling of influenza C virus-infected HMV-II cells with [32P]orthophosphate showed that the CM2 protein is posttranslationally modified by phosphorylation [8].

Analytical, diagnostic and therapeutic context of CM2

• Three forms of CM2 with different electrophoretic mobilities (CM2(0), CM2a, and CM2b) were detected in infected cells by immunoprecipitation with antiserum to the glutathione S-transferase (GST)-CM2 fusion protein [2].

References