Sequence characterization of the matrix protein genes of parainfluenza virus types 4A and 4B

This study determined the complete nucleotide sequences of the matrix protein (M) genes of human parainfluenza virus types 4A and 4B (hPIV-4A and hPIV-4B). Both genes were 1548 bases long, encoding 362 amino acids with predicted molecular weights around 43 kDa. The M protein sequences showed 96.1% amino acid identity between the two subtypes, supporting their classification as separate serotypes. Comparison with matrix proteins from 10 other paramyxoviruses revealed that hPIV-4 is most closely related to mumps virus, with moderate similarity to parainfluenza type 2 and simian virus 5. Phylogenetic analysis divided paramyxoviruses into two groups, with hPIV-4 clustering with mumps virus. While 96.1% sequence identity between hPIV-4A and 4B M proteins was observed, monoclonal antibody cross-reactivity was only 57%, suggesting that the tertiary structure of the matrix protein, rather than primary sequence alone, determines its antigenicity. The matrix proteins are highly positively charged and hydrophobic, properties important for their roles in virion assembly and viral pathogenesis.

Key findings

• The M genes of hPIV-4A and hPIV-4B are 1548 bases long, encoding 362 amino acids with 96.1% sequence identity between subtypes
• Matrix proteins are highly positively charged (+22.5 net charge) and hydrophobic (~48% hydrophobic residues), suggesting roles in virion structure
• Phylogenetic analysis places hPIV-4 in a group with mumps virus, separate from Sendai virus and PIV-3, based on M protein comparisons
• Tertiary structure rather than primary sequence appears to determine matrix protein antigenicity, as 96% sequence identity correlates with only 57% monoclonal antibody cross-reactivity