  Comparison of properties of three domains of titin, I1, I27 and I28, in a
simple geometry-based model shows that despite a high structural homology
between their native states different domains show similar but distinguishable
mechanical properties. Folding properties of the separate domains are predicted
to be diversified which reflects sensitivity of the kinetics to the details of
native structures. The Go-like model corresponding to the experimentally
resolved native structure of the I1 domain is found to provide the biggest
thermodynamic and mechanical stability compared to the other domains studied
here. We analyze elastic, thermodynamic and kinetic properties of several
structures corresponding to the I28 domain as obtained through homology-based
modeling. We discuss the ability of the models of the I28 domain to reproduce
experimental results qualitatively. A strengthening of contacts that involve
hydrophobic amino acids does not affect theoretical comparisons of the domains.
Tandem linkages of up to five identical or different domains unravel in a
serial fashion at low temperatures. We study the nature of the intermediate
state that arises in the early stages of the serial unraveling and find it to
qualitatively agree with the results of Marszalek et al.
