Table 1. Binding free energies (kcal/mol) between PBP2x protein and cefuroxime (CES) in the two complexes.

Method	Contribution	Complex
		PBP2x-R61-CES	PBP2x-A7-CES
MM	ELE	−12.7±3.9	−24.0±4.9
	VDW	−41.6±3.3	−58.1±2.9
	INT	0.0±0.2	0.0±1.1
	GAS	−54.2±4.9	−82.1±5.9
PBSA	PBSUR	−5.9±0.3	−6.1±0.1
	PBCAL	42.9±5.9	51.7±4.3
	PBSOL	37.0±5.8	45.6±4.3
	PBELE	30.2±4.1	27.7±2.9
	PBTOT	−17.2±4.2	−36.4±4.9
GBSA	GBSUR	−5.9±0.3	−6.1±0.1
	GB	31.7±3.5	39.6±3.6
	GBSOL	25.8±3.4	33.5±3.6
	GBELE	19.0±2.0	15.6±2.3
	GBTOT	−28.4±3.1	−48.6±3.7

ELE, electrostatic interactions; VDW, van der Waals interactions between the fragments; INT, internal energy arising from bond, angle and dihedral terms in the MM force field; GAS, total gas phase energy (sum of ELE, VDW and INT); PBSUR/GBSUR, nonpolar contribution to solvation; PBCAL/GB, the electrostatic contribution to the solvation free energy calculated by PB or GB respectively; PBSOL/GBSOL, sum of nonpolar and polar contributions to solvation; PBELE/GBELE, sum of the electrostatic solvation free energy and MM electrostatic energy; PBTOT/GBTOT, estimated total binding free energy calculated from the terms above.