Newcastle disease virus nucleocapsid protein: self-assembly and length-determination domains

This study investigates the structural domains of Newcastle disease virus (NDV) nucleocapsid protein (NP) responsible for self-assembly. Researchers created 11 N- or C-terminally deleted NP mutants expressed in E. coli and analyzed their ability to form ring- and herringbone-like particles using electron microscopy and sucrose gradient centrifugation. Results demonstrate that amino acids 1-375 at the N-terminal end are essential for proper folding and herringbone-like particle formation, while the C-terminal region (amino acids 376-489) is dispensable for assembly. However, a region between amino acids 375-439 appears to regulate particle length; mutants with larger C-terminal deletions formed longer particles compared to those with shorter deletions. The N-terminal 25 amino acids are critical for proper NP-NP interactions, and deletions beyond 121 residues completely prevented regular structure formation. These findings identify the NP self-assembly domain in NDV and suggest the C-terminus plays a regulatory rather than essential role in nucleocapsid polymerization.

Key findings

• The N-terminal region encompassing amino acids 1-375 is essential for NDV nucleocapsid protein self-assembly and proper folding into herringbone-like structures
• The C-terminal region (amino acids 376-489) is dispensable for particle assembly but may regulate the length of herringbone-like particles through control of NP polymerization
• Deletions of amino acids 375-439 from the C-terminus result in formation of longer herringbone-like particles, suggesting this region negatively regulates protein polymerization
• The N-terminal 25 amino acids are critical for proper NP-NP interactions necessary for assembly
• Loss of the first 121 N-terminal amino acids completely abolishes formation of regular, ordered nucleocapsid-like structures