Figure 1
The design of PiTou algorithm: the PiTou score function 
is biological knowledge-based and it comprises of a machine learning-based hidden Markov model and a set of biological mechanism-based cumulative probability score functions.
is the sum of two parts: the core region binding score 
(calculated from eight amino acids at P6–P2′) and the flanking region solvent accessible score 
(calculated from eight amino acids at P7–P14 and four amino acids at P3′–P6′). 
and 
incorporate the physical properties of the 20-residue furin cleavage motif and the binding of substrates to the furin catalytic domain. The analysis of the 20-residue furin cleavage motif is described in previous publication8.
