Table 4. The hydrogen bond interactions between the p21^WAF1 (PDB-id: 1AXC) and small molecules - withaferin A and withanone.

Protein	Small molecule	Hydrogen bond interactions	Distance (Å)	Binding energy (Kcal/mol)
p21WAF1 (PDB-id: 1AXC)	Withaferin A	Met (147) O2-H…O	2.44	−7.84
		Tyr (151) N-H…O2	3.37
		His (152) O-H…O1	2.67
		Ile (158) N-H…O6	3.40
		Arg (156) O6-H…O	2.81
		Arg (156) O-H…O4	2.79
		Arg (156) N-H…O5	3.07
		Arg (155) NH1-H…O4	2.71
	Withanone	Lys (154) N-H…O2	2.63	−7.84
		Lys (154) O2-H…O	2.65
		Arg (156) N-H…O4	2.59
		Arg (156) O4-H…O	2.84
		Ile (158) N-H…O5	2.81