Table 3. Computed H-bond disruption probability −RTlnP and free energy change Δ^H_theor at 293 K along with observed H-bond free energy change ΔG_expt from protein engineering in T4 lysozyme (PDB id: 3LZM) and ribonuclease T1 (PDB id: 9RNT).

Protein	H-bonded atom	H-bonded partner	H-bond type	Partner % burieda	〈rl〉 Å	−RTlnPl kcal/mol	ΔHtheor kcal/mol	ΔGexpt kcal/mol
T4 lysozymeb	OG1 THR157	OD1 ASP159	Normal	0	2.95	2.08	0	1.6
Ribonuclease T1b	ND2 ASN9	OD2 ASP76	Normal	57	2.97	1.80	1.0	1.6
	OH TYR11	OD2 ASP76	3-centre	97	2.89	3.82	5.49	3.2
		O ILE61		97	2.97	1.84
	OG SER12	OD2 ASP15	Normal	55	2.95	2.17	1.19	1.4
	OD1 ASN36	OG SER35	Normal	30	2.93	2.53	0.76	0.6
	ND2 ASN44	O PHE48	Normal	76	3.26	0.54	0.41	2.5
	OD1 ASN44	N PHE48	3-centre	88	2.96	1.99	4.21
		OH TYR42		97	2.93	2.54
	OH TYR56	O VAL 52	Normal	73	2.91	2.91	2.12	1.8
	OH TYR 57	OE1 GLU82	Normal	70	2.86	5.21	3.64	1.4
	OG SER 64	OD2 ASP66	Normal	0	2.97	1.79	0	1.7
	OH TYR68	O GLY71	Normal	31	2.88	4.18	1.30	2.5
	ND2 ASN81	O SER53	Normal	24	3.05	1.18	0.28	3.5
	OD1 ASN81	N ASN83	3-centre	16	2.98	1.72	1.02
		N GLN 85		47	2.99	1.57

The observed value for T4 lysozyme is from Alber et al. (54) and those for ribonuclease T1 are from Shirley et al. (55). H-bond partners at the experimental mutation sites are included. Calculated mean bond length 〈r_l〉 is also listed.

^aSolvent accessibility is from Shirley et al. (55), and Sybyl6.5 (58).

^bIn the T4 lysozyme, Thr→Val; in ribonuclease T1, all Tyr→Phe, Ser→Ala, Asn→Ala, (see text).