[The anomalous isoelectric properties of influenza virus matrix protein M1]

Area of Science:

• Virology
• Protein Chemistry
• Biochemistry

Background:

• The matrix protein M1 is a key structural component of influenza viruses.
• Understanding M1 protein properties is crucial for viral assembly and function.

Purpose of the Study:

• To investigate the discrepancy between theoretical and experimental isoelectric points (pI) of influenza virus matrix protein M1.
• To explore potential reasons for the observed pI difference, including tertiary structure and posttranslational modifications.

Main Methods:

• Theoretical calculation of M1 protein pI based on primary amino acid sequence.
• Experimental determination of M1 protein pI using electrofocusing in polyacrylamide gel.
• Isolation of M1 protein from influenza A virus strains using mild deproteinization with nonionic detergents.

Main Results:

• Theoretical pI calculations predicted a value of approximately 10.0 for M1 protein.
• Experimental pI determination revealed a significantly lower value of 5.0 for M1 protein from influenza A/WSN/33 (H1N1) and A/Aichi/2/68 (H3N2) viruses.
• A notable discrepancy exists between the theoretical and experimental pI values.

Conclusions:

• The significant difference between theoretical and experimental pI suggests M1 protein has an unusual tertiary structure.
• Posttranslational addition of charged residues may also contribute to the observed pI anomaly.
• These findings highlight the complex nature of influenza virus M1 protein structure and properties.