Single-molecule measurement of elasticity of serine-, glutamate- and lysine-rich repeats of invertebrate connectin reveals that its elasticity is caused entropically by random coil structure.
Invertebrate connectin (I-connectin) is a 1960 kDa elastic protein linking the Z line to the tip of the myosin filament in the giant sarcomere of crayfish claw closer muscle (Fukuzawa et al., 2001 EMBO J 20: 4826-4835). I-Connectin can be extended up to 3.5 microns upon stretch of giant sarcomeres. There are several extensible regions in I-connectin: two long PEVK regions, one unique sequence region and Ser-, Glu- and Lys-rich 68 residue-repeats called SEK repeats. In the present study, the force measurement of the single recombinant SEK polypeptide containing biotinylated BDTC and GST tags at the N and C termini, respectively, were performed by intermolecular force microscopy (IFM), a refined AFM system. The force vs. extension curves were well fit to the wormlike chain (WLC) model and the obtained persistence length of 0.37 +/- 0.01 nm (n = 11) indicates that the SEK region is a random coil along its full length. This is the first observation of an entropic elasticity of a fully random coil region that contributes to the physiological function of I-connectin.
Fukuzawa
Atsushi
A
Department of Biology, Faculty of Science, Chiba University, Chiba, 263-8522, Japan.
Hiroshima
Michio
M
Maruyama
Koscak
K
Yonezawa
Naoto
N
Tokunaga
Makio
M
Kimura
Sumiko
S
D000595:Amino Acid Sequence; D000818:Animals; D064211:Connectin; D004548:Elasticity; D006801:Humans; D007448:Invertebrates; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D009124:Muscle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics
D064211:Connectin; D009124:Muscle Proteins; D011994:Recombinant Proteins; C577285:TTN protein, human; D011494:Protein Kinases