Calcium-dependent molecular spring elements in the giant protein titin.
Titin (also known as connectin) is a giant protein with a wide range of cellular functions, including providing muscle cells with elasticity. Its physiological extension is largely derived from the PEVK segment, rich in proline (P), glutamate (E), valine (V), and lysine (K) residues. We studied recombinant PEVK molecules containing the two conserved elements: approximately 28-residue PEVK repeats and E-rich motifs. Single molecule experiments revealed that calcium-induced conformational changes reduce the bending rigidity of the PEVK fragments, and site-directed mutagenesis identified four glutamate residues in the E-rich motif that was studied (exon 129), as critical for this process. Experiments with muscle fibers showed that titin-based tension is calcium responsive. We propose that the PEVK segment contains E-rich motifs that render titin a calcium-dependent molecular spring that adapts to the physiological state of the cell.
Labeit
Dietmar
D
Anästhesiologie und Operative Intensivmedizin, Universitätsklinikum Mannheim, 68167 Mannheim, Germany.
Watanabe
Kaori
K
Witt
Christian
C
Fujita
Hideaki
H
Wu
Yiming
Y
Lahmers
Sunshine
S
Funck
Theodor
T
Labeit
Siegfried
S
Granzier
Henk
H
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D064211:Connectin; D005091:Exons; D017353:Gene Deletion; D018698:Glutamic Acid / Q000737:chemistry; D006801:Humans; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry*; D009132:Muscles / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011392:Proline / Q000737:chemistry; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D014633:Valine / Q000737:chemistry
D064211:Connectin; D009124:Muscle Proteins; D011994:Recombinant Proteins; C577285:TTN protein, human; D018698:Glutamic Acid; D011392:Proline; D011494:Protein Kinases; D014633:Valine; D008239:Lysine; D002118:Calcium