The folding and stability of titin immunoglobulin-like modules, with implications for the mechanism of elasticity.
Titin (first known as connectin) is a vast modular protein found in vertebrate striated muscle. It is thought to assist myofibrillogenesis and to provide a passive elastic restoring force that helps to keep the thick filaments properly centered in the sarcomere. We show that representative titin modules do indeed fold independently, and report their stabilities (i.e., delta G of unfolding and melting temperature) as measured by circular dichroism, fluorescence, and nuclear magnetic resonance spectroscopies. We find that there is a region-dependent variation in stability, although we find no evidence to support a proposed elastic mechanism based on a molten-globular-like equilibrium folding intermediate, nor do our calculations support any mechanism based on the configurational entropy of the molecule itself; instead we suggest a model based on hydrophobic hinge regions that would not be strongly dependent on the precise folding pattern of the chain.
Politou
A S
AS
European Molecular Biology Laboratory, Heidelberg, Germany. politou@embl-heidelberg.de
Thomas
D J
DJ
Pastore
A
A
D000818:Animals; D002942:Circular Dichroism; D064211:Connectin; D004355:Drug Stability; D004548:Elasticity; D006639:Histidine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007136:Immunoglobulins / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism*; D018482:Muscle, Skeletal; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016324:Sequence Tagged Sites; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014508:Urea; D014714:Vertebrates
D064211:Connectin; D007136:Immunoglobulins; D009124:Muscle Proteins; D011994:Recombinant Proteins; C577285:TTN protein, human; D006639:Histidine; D014508:Urea; D011494:Protein Kinases