The Dictyostelium gelation factor shares a putative actin binding site with alpha-actinins and dystrophin and also has a rod domain containing six 100-residue motifs that appear to have a cross-beta conformation.
The 120-kD gelation factor and alpha-actinin are among the most abundant F-actin cross-linking proteins in Dictyostelium discoideum. Both molecules are homodimers and have extended rod-like configurations that are respectively approximately 35 and 40 nm long. Here we report the complete cDNA sequence of the 120-kD gelation factor which codes for a protein of 857 amino acids. Its calculated molecular mass is 92.2 kD which is considerably smaller than suggested by its mobility in SDS-PAGE. Analysis of the sequence shows a region that is highly homologous to D. discoideum alpha-actinin, chicken fibroblast alpha-actinin, and human dystrophin. This conserved domain probably represents an actin binding site that is connected to the rod-forming part of the molecule via a highly charged stretch of amino acids. Whereas the sequence of alpha-actinin (Noegel, A., W. Witke, and M. Schleicher. 1987. FEBS [Fed. Eur. Biochem. Soc.] Lett. 221:391-396) suggests that the extended rod domain of the molecule is based on four spectrin-like repeats with high alpha-helix potential, the rod domain of the 120-kD gelation factor is constructed from six 100-residue repeats that have a high content of glycine and proline residues and which, in contrast to alpha-actinin, do not appear to have a high alpha-helical content. These repeats show a distinctive pattern of regions that have high beta-sheet potential alternating with short zones rich in residues with a high potential for turns. This observation suggests that each 100-residue motif has a cross-beta conformation with approximately nine sheets arranged perpendicular to the long axis of the molecule. In the high beta-potential zones every second residue is often hydrophobic. In a cross-beta structure, this pattern would result in one side of the domain having a surface rich in hydrophobic side chains which could account for the dimerization of the 120-kD gelation factor subunits.
Noegel
A A
AA
Max-Planck-Institut, Martinsried, Federal Republic of Germany.
Rapp
S
S
Lottspeich
F
F
Schleicher
M
M
Stewart
M
M
D000185:Actinin / Q000032:analysis* / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000032:analysis* / Q000378:metabolism; D004247:DNA / Q000032:analysis / Q000235:genetics; D004023:Dictyostelium / Q000032:analysis*; D016189:Dystrophin; D008840:Microfilament Proteins / Q000032:analysis* / Q000378:metabolism; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000032:analysis* / Q000378:metabolism; D011487:Protein Conformation
D000199:Actins; D002352:Carrier Proteins; D016189:Dystrophin; D008840:Microfilament Proteins; D009124:Muscle Proteins; D000185:Actinin; C060680:abpC protein, Dictyostelium; D004247:DNA