A long helix from the central region of smooth muscle caldesmon.
The central region of smooth muscle caldesmon is predicted to form alpha-helices on the basis of its primary structure. We have isolated a fragment (CT54) that contains this region. The hydrodynamic properties and the electron microscopic images suggest that CT54 is an elongated (35 nm), monomeric molecule. The circular dichroic spectrum yields an overall alpha-helical content of 55-58%. These results are consistent with the model that the middle portion of CT54 forms a long stretch of single-stranded alpha-helix. Such a structure, if it in fact exists, is thought to be stabilized by numerous salt bridges between charged residues at positions i and i + 4. The structural characteristics of this fragment not only represent an unusual protein configuration but also provide information about the functional role of caldesmon in smooth muscle contraction.
Wang
C L
CL
Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114.
Chalovich
J M
JM
Graceffa
P
P
Lu
R C
RC
Mabuchi
K
K
Stafford
W F
WF
D000595:Amino Acid Sequence; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000737:chemistry / Q000648:ultrastructure*; D002918:Chymotrypsin; D002942:Circular Dichroism; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D014422:Turkeys
D002148:Calmodulin-Binding Proteins; D010446:Peptide Fragments; D002918:Chymotrypsin