Fig. 2.

Frequency of amino acid residues found at the P2 position of all the known cleavage sequences of furin and furin-like enzymes. The cleavage sequences of the form P4P3P2P1P1′P2′P3′P4′ archived in the MEROPS database were extracted. Each amino acid present at the P2 position was counted and normalized to the total observed sites. Note that the basic residues R/K contribute to about 80% of the P2 residues.