Sandbox WWC8: Difference between revisions

The globular NP protein is rich in arginine, serine, and glycine residues. The abundance of arginine residues gives the protein a net positive charge at pH 7. With a predicted pI of 9.3, NP is mainly composed of basic residues, except for a tail domain of the 30 C-terminal residues, which are acidic. The C-tail domain has a pI of 3.7. The NP is a homo 3-mer - A3 with 499 amino acid residues encoded by the Influenza A RNA segment 5.Each homomer provides a binding site for the viral RNA script. The homomers fold into a crescent shape with a head and a body domain, where the grove between the two domains hosts the ssRNA binding site on the outer surface of the homomer. For the formation of RNPs, the NP needs to oligomerize, forming a coordinated aggregate of three NPs. The C-tail loop, marked in pink in the image below, is critical for this function. Residues 408-419, located at the back of the NP between head and tail domain, form a loop that is the basis of the interface between neighboring NPs. The C-tail loop interlock with the loop binding cavity in the neighboring NP and form a tight binding interaction, featuring both hydrophobic and hydrophilic residues, that keeps the homo 3-mer together. The NP oligomer conformation is especially stabilized by a salt bridge between Arg 416 in the loop and Glu339 in the adjacent NP.