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.
Hnath
E J
EJ
Department of Biochemistry and Cell Biology, W.M. Keck Center for Computational Biology, Rice University, Houston, Texas 77005, USA.
Wang
C L
CL
Huber
P A
PA
Marston
S B
SB
Phillips
G N
GN
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