Table 3.

Statistics on the occurrence of different combinations of β-turns within the common π-turns.

π-turn	Multiple β-turns with their designationsa
π-HB
AAAa (350)	I-I-X (270), X-I-X (60), I-X-X (17)
PgAA (52)	II-X-X (40), II-X-I (8), X-X-I (1)
AAAA (33)	I-X-X (21), I-I-X (6), I-I-I (2), X-I-I (1), X-I-X (1)
π-NHB
AEAA (316)	X-X-I (253), VIII-X-I (45), VIII-X-X (4), X-VIa2-I (1)
EAAa (281)	X-I-X (270)
EAAA (219)	X-I-I (156), X-I-X (44), X-X-I (12)
EAAE (176)	X-I-X (130), X-I-VIII (16), VIa1-X-VIII (1), VIa1-I-X (1)
AAaA (171)	I-X-X (146)
AEEa (167)	X-X-II (131), VIII-X-II (20), X-VIb-II (1)

The number of occurrence is given in parentheses.

^a X indicates no characteristic β-turn. The conventional nomenclature of β-turns (viz., turn types I, II, VI, VIII, etc.) has been used. A multiple turn I-I-X indicates that there is a type I turn involving residues (i)-(i+3), another type I involving (i+1)-(i+4), and the turn type involving (i+2)-(i+5) does not conform to any β-turn type.