Abstract
The A-band part of titin, a striated-muscle specific protein spanning from the Z-line to the M-line, mainly consists of a well-ordered super-repeat array of immunoglobulin-like and fibronectin-type III (fn3)-like domains. Since it has been suspected that the fn3 domains might represent titin's binding sites to myosin, we have developed structural models for all of titin's 132 fn3-like domains. A subset of eight experimentally determined fn3 structures from a range of proteins, including titin itself, was used as homology templates. After grouping the models according to their position within the super-repeat segment of the central A-band titin region, we analyzed the models with respect to side-chain conservation. This showed that conserved residues form an extensive surface pattern predominantly at one side of the domains, whereas domains outside the central C-zone super-repeat region show generally less conserved surfaces. Since the conserved surface residues may function as protein-binding sites, we experimentally studied the binding properties of expressed multi-domain fn3 fragments. This revealed that fn3 fragments specifically bind to the sub-fragment 1 of myosin. We also measured the effect of fn3 fragments on the contractile properties of single cardiac myocytes. At sub-maximal Ca2+ concentrations, fn3 fragments significantly enhance active tension. This effect is most pronounced at short sarcomere length, and as a result the length-dependence of Ca2+ activation is reduced. A model of how titin's fn3-like domains may influence actomyosin interaction is proposed.
Original language | English (US) |
---|---|
Pages (from-to) | 431-447 |
Number of pages | 17 |
Journal | Journal of Molecular Biology |
Volume | 313 |
Issue number | 2 |
DOIs | |
State | Published - Oct 19 2001 |
Keywords
- Fibronectin type III
- Molecular modeling
- Muscle contraction
- Striated muscle
- Titin
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology