BIOINORGANIC CHEMISTRY A Short Course Second Edition

312 GROUP I AND II METALS IN BIOLOGICAL SYSTEMS: GROUP II

The same authors then studied the formation of ternary complexes with
calmodulin, TFP and two bisindole drug molecules: vinblastine and KAR - 2
(structures shown in Figure 6.25 ) using the near - UV CD method. They found
that both TFP and KAR - 2 are able to bind to calmodulin simultaneously
forming a ternary species but that vinblastine is not able to bind to a TFP:CaM
complex. If the CD experiment was repeated under conditions in which the

Figure 6.26 Calmodulin:2trifl uoroperazine complex, PDB: 1A29. Visualized using
CambridgeSoft Chem3D Ultra 10.0 with notations in ChemDraw Ultra 10.0. (Printed
with permission of CambridgeSoft Corporation.)

C-terminal TFP

interdomain

TFP

glu31

(behind)

asp20

(front)

asp22

asp24

thr26

asp56

(behind)

glu67

(front)

thr62

asn60

asp58

PDB: 1A29

TABLE 6.8 Bond Distances for the 1:2 CaM:TFP

Complex (PDB: 1A29) Ca 2+ at Site I

Ligand, Ligand Atom

Bond Distance to Ca 2+

at Site I ( Å )

asp20, O δ 1 2.29

asp22, O δ 1 2.29

asp24, O δ 1 2.29

thr26, backbone O 2.28

glu31, O ε 1 2.33

glu31, O ε 2 2.29