Modular motif, structural folds and affinity profiles of the PEVK segment of human fetal skeletal muscle titin.
The extension of the PEVK segment of the giant elastic protein titin is a key event in the elastic response of striated muscle to passive stretch. PEVK behaves mechanically as an entropic spring and is thought to be a random coil. cDNA sequencing of human fetal skeletal PEVK reveals a modular motif with tandem repeats of modules averaging 28 residues and with superrepeats of seven modules. Conformational studies of bacterially expressed 53-kDa fragment (TP1) by circular dichroism suggest that this soluble protein contains substantial polyproline II (PPII) type left-handed helices. Urea and thermal titrations cause gradual and reversible decrease in PPII content. The absence of sharp melting in urea and thermal titrations suggests that there is no long range cooperativity among the PPII helices. Studies with solid phase and surface plasmon resonance assays indicate that TP1 interacts with actin and some but not all cloned nebulin fragments with high affinity. Interestingly, Ca(2+)/calmodulin and Ca(2+)/S100 abolish nebulin/PEVK interaction. We suggest that in aqueous solution, PEVK is an open and flexible chain of relatively stable structural folds of the polyproline II type. PEVK region of titin may be involved in interfilament association with thin filaments in a calcium/calmodulin-sensitive manner. This adhesion may modulate titin extensibility and elasticity.
Gutierrez-Cruz
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Laboratory of Physical Biology, NIAMS, National Institutes of Health, Bethesda, Maryland 20892, USA.
Van Heerden
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AH
Wang
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D000199:Actins / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002448:Cell Adhesion; D002942:Circular Dichroism; D003001:Cloning, Molecular; D064211:Connectin; D018076:DNA, Complementary / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006358:Hot Temperature; D006801:Humans; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000196:embryology*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011392:Proline / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry*; D016601:RNA-Binding Proteins; D009418:S100 Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance; D013696:Temperature; D013997:Time Factors; D014508:Urea / Q000494:pharmacology
D000199:Actins; D002147:Calmodulin; D002352:Carrier Proteins; D064211:Connectin; D018076:DNA, Complementary; D009124:Muscle Proteins; D010455:Peptides; D016601:RNA-Binding Proteins; D009418:S100 Proteins; C110294:S100A1 protein; C104342:TEP1 protein, human; C577285:TTN protein, human; C035620:nebulin; C011083:polyproline; D014508:Urea; D011392:Proline; D011494:Protein Kinases; D002118:Calcium