TABLE 1.

Some ligands and receptors of interest for drug targeting and other biophysical research

Ligand	Receptor	Bond energy W/kBT*	Dissociation constant Kd (M)*	Ligand MW (D)	Reference
Folic acid	Folate receptor	21–25	10−9 − 10−11	441	(68,69)
Sialyl Lewis X†	L-selectin	18–24	2×10−8 − 4×10−11	120,000	(70–72)
PSGL1	P-selectin	17	5.5 × 10−8	120,000	(72,73)
Adenine (A)	Thymine (T)	2.3	1 × 10−1	135	(74)
RGD peptide	Integrin αIIβ3	14	1 × 10−6	770	(75)
fibrinogen	Integrin αIIβ3	16	1 × 10−7	N/A	(75)
145-2C11 mAb (antibody)	CD3	16	7 × 10−8	N/A	(76,77)
Fluorescein	Anti-fluorescein	19–21	0.75–8.9 × 10−9	380	(78)
Human serum albumin (HSA)	Anti-HSA	14‡	8.3 × 10−7	66,500	(79)
Serine endopeptidases (various)	Protein inhibitor	18–29	1.5 × 10−8 − 2.5 × 10−13	N/A	(77)
“Typical” antibody	“Typical” antigen	18	10−8	>100,000	(22,73)
Biotin	Avidin	35	1.0 × 10−15	244	(80)
Biotin analogues (various)	Streptavidin	5–30	1.0 × 10−2 − 5 × 10−8	214–258	(80,81)

^*When only one of W or K_d was reported, the other was estimated (22).

^†Modified PSGL-1 ligand.

^‡Estimated as W = (rupture force) × (effective rupture length) (22).