Table 2.

Characteristic ϕ/ψ torsion angles, C^α distances and intra-turn hydrogen bonds for five types of β-turns.

Type (k)	Torsion Anglesa						Nb	Cα(i,i+3) distance [Å]	H-bond (i←i+3 /(i→i+3)c [%]	Energy (i←i+3)d [kcal/mol]
	ϕi+1,k	ψi+1,k	ϕi+2,k	ψi+2,k	(ϕ+ψ)i+1,k	(ϕ+ψ)i+2,k
Ie	(−64) −65±12	(−27) −24±13	(−90) −93±16	(−7) −3±17	−89±14	−95±19	34337	5.5±0.4	80/10	−1.7±0.6
II	(−60) −61±13	(131) 136±11	(84) 80±16	(1) 5±20	75±14	85±11	15690	5.7±0.4	90/4	−1.8±0.6
I’	(55) 53±7	(38) 40±10	(78) 77±12	(6) 5±15	93±7	83±9	5238	5.4±0.3	95/84	−1.8±0.5
II’	(60) 60±9	(−126) −126±11	(−91) −93±13	(1) 5±16	−66±14	−88±12	3522	5.5±0.4	95/64	−2.0±0.6
VIII	(−72) −76±15	(−33) −32±14	(−123) −131±20	(121) 131±23	−108±16	0±25	14879	6.5±0.5	0.6/0.2	−0.7±0.2

^aThe average ϕ/ψ torsion angles of the two center residues (residues i+1 and i+2) of the isolated β-turns observed in the structure database (SI Fig. S1 D–H). The ideal ϕ/ψ torsion angles of the two center residues for five types β-turns (Hutchinson and Thornton 1994) are given in parentheses.

^bNumber of isolated β-turns in the structure database, which are not overlapped with other β-turns.

^cPercentage of the isolated β-turns in the structure database with bb(i)←bb(i+3) and bb(i)→bb(i+3) H-bonds between the first and the last residue.

^dElectrostatic interaction energy (Kabsch and Sander 1983) of the bb(i)←bb(i+3) H-bond between the C=O of residue i and N-H of residue i+3 in all isolated β-turns in the structure database.

^eFor type I turns, the sum of ψ_i+1 and ϕ_i+2 is also used in Eq 5, with a value of −118+20° degree (see Methods).