Table 3.

Conformation of Pro and its 4-substituted derivatives that prefer the Xaa position [φ = −75°, ψ = 164° (7)] in a collagen triple helix.

Residue (References)		Crystal structure	Ring pucker	(Eendo− Eexo)a (kcal/mol)	φ (degrees)	ψ degrees)	Ktrans/cisc
Pro (54, 56, 57)			Cγ- endo	−0.41	−79b	177b	4.6
mcp (66)		–-	Cγ- endo	–-	–-	–-	4.7
mep (65)		–-	Cγ- endo	−1.4	–-	–-	3.7
flp (54, 56, 68)		–-	Cγ- endo	−0.61	−76a	172a	2.5
clp (61)		–-	Cγ- endo	–-	–-	–-	2.2

^aFrom DFT calculations.

^bValues of φ and ψ (here, N_i–C^α _i–C′_i–O_i+1) are from the crystal structure of Ac-Pro-OMe, which has a cis peptide bond.

^cValues of K_trans/cis(Figure 5) were determined in solution by NMR spectroscopy.