Physical characterization of calponin. A circular dichroism, analytical ultracentrifuge, and electron microscopy study.
Calponin is a thin filament-associated smooth muscle protein that has been suggested to play a role in the regulation of smooth muscle contraction. We have used circular dichroism spectroscopy, electron microscopy, and analytical ultracentrifugation to study the physical properties of recombinant chicken gizzard alpha-calponin. The alpha-helix content of alpha-calponin was estimated from its circular dichroism spectrum to be approximately 13%, alpha-Calponin melts with a single sharp transition at approximately 57 degrees C. Rotary shadowing electron micrographs of alpha-calponin reveal diverse shapes ranging from elongated rods to collapsed coils. The lengths of the rod-shaped structures are approximately 18 nm. Analytical ultracentrifugation studies found alpha-calponin to be homogeneous with a monomer molecular mass of 31.4 kDa, and a s20,w value of 2.34 S. These data could be used to model alpha-calponin as a prolate ellipsoid of revolution with an axial ratio of 6.16, a length of 16.2 nm, and a diameter of 2.6 nm. Taken together, our results indicate that calponin is a flexible, elongated molecule whose contour length is sufficient to span three actin subunits along the long pitch helix of an F-actin filament.
Stafford
W F
WF
Muscle Research Group, Boston Biomedical Research Institute, Boston, Massachusetts 02114, USA.
Mabuchi
K
K
Takahashi
K
K
Tao
T
T
D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000648:ultrastructure; D002645:Chickens; D002942:Circular Dichroism; D006358:Hot Temperature; D008840:Microfilament Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000737:chemistry; D011489:Protein Denaturation; D011994:Recombinant Proteins; D014461:Ultracentrifugation; D000096985:Calponins
D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D011994:Recombinant Proteins; D000096985:Calponins