Table 2.

Amino acid attributes and the division of the amino acids into three groups for each attribute

Attribute	Divisions
Hydrophobicity	Polar	Neutral	Hydrophobicity
	R,K,E,D,Q,N	G, A, S,T,P,H,Y	C,L,V,I,M,F,W
Normalized van der Waals volume	Volume range 0–2.78	Volume range 2.95–94.0	Volume range 4.03–8.08
	G,A,S,T,P,D	N,V,E,Q,I,L	M,H,K,F,R,Y,W
Polarity	Polarity value 4.9–6.2	Polarity value 8.0–9.2	Polarity value 10.4–13.0
	L,I,F,W,C,M,V,Y	P,A,T,G,S	H,Q,R,K,N,E,D
Polarizability	Polarizability value 0–1.08	Polarizability value 0.128–120.186	Polarizability value 0.219–0.409
	G,A,S,D,T	C,P,N,V,E,Q,I,L	K,M,H,F,R,Y,W
Charge	Positive	Neutral	Negative
	KR	ANCQGHILMFPSTWYV	DE
Secondary structure	Helix	Strand	Coil
	EALMQKRH	VIYCWFT	GNPSD
Solvent accessibility	Buried	Exposed	Intermediate
	ALFCGIVW	PKQEND	MPSTHY

The division is based on the clusters of the amino acid indices of Tomii and Kanehisa (5,40) for each of the seven attributes. For such attributes as secondary structure and solvent accessibility, the division is based on statistical appearance of each amino acid in a specific state.