Affinity and structure of complexes of tropomyosin and caldesmon domains.
The interaction of caldesmon domains with tropomyosin has been studied using x-ray crystallography and an optical biosensor. Only whole caldesmon and the carboxyl-terminal domain of caldesmon (CaD-4, chicken gizzard residues 597-756) bound to tropomyosin with greater than millimolar affinity at 100 and 150 microM salt. Under these conditions the affinities of whole caldesmon and CaD-4 were both in the micromolar range. Data from the x-ray studies showed that whole caldesmon bound to tropomyosin in several places, with the region of tightest interaction being at tropomyosin residues 70-100 and/or 230-260. Studies with CaD-4 revealed that this region corresponded to the strong binding site seen with whole caldesmon. Weaker association of other regions of caldesmon to tropomyosin residues 180-210 and 5-50 was also observed. The results suggest that the carboxyl-terminus of caldesmon binds tightly to tropomyosin and that other regions of caldesmon may interact with tropomyosin tightly only when they are held close to tropomyosin by the carboxyl-terminal domain. Four models are presented to show the possible interactions of caldesmon with tropomyosin.
Department of Biochemistry and Cell Biology, W.M. Keck Center for Computational Biology, Rice University, Houston, Texas 77005, USA.
E J
EJ
Hnath
C L
CL
Wang
P A
PA
Huber
S B
SB
Marston
G N
GN
Phillips
D000818:Animals; D001665:Binding Sites; D015374:Biosensing Techniques; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D002645:Chickens; D003460:Crystallization; D018360:Crystallography, X-Ray; D005895:Gizzard, Avian; D007700:Kinetics; D008961:Models, Structural; D018482:Muscle, Skeletal / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D014335:Tropomyosin / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*
D002148:Calmodulin-Binding Proteins; D010446:Peptide Fragments; D014335:Tropomyosin