phage major coat protein phage major coat protein in molecular biology, a phage major coat protein is an alpha-helical protein that forms a viral envelope of filamentous bacteriophages. these bacteriophages are flexible rods, about one to two micrometres long and six nm in diameter, with a helical shell of protein subunits surrounding a dna core. the approximately 50-residue subunit of the major coat protein is largely alpha-helix, and the axis of the alpha-helix makes a small angle with the axis of the virion. the protein shell can be considered in three sections: the outer surface, occupied by the n-terminal region of the subunit and rich in acidic residues that give the virion a low isoelectric point; the interior of the shell (including a 19-residue stretch of apolar side-chains) where protein subunits interact, mainly with each other; and the inner surface (occupied by the c-terminal region of the subunit), rich in positively charged residues that interact with the dna core. phage coat gp8single subunit of coat proteinidentifierssymbolphage_coat_gp8pfampf05371pfam clancl0371interproipr008020scop21fdm / scope / supfamopm superfamily67opm protein1ifkavailable protein structures:pfam structures / ecod pdbrcsb pdb; pdbe; pdbjpdbsumstructure summary