Fig. 1
Conserved cysteine positions in the I65–I70 fragment of titin. a Schematic architecture of one half of the sarcomere. The titin filament spans across the contractile unit and its elastic properties arise from its extensible I-band region where Ig modules (filled black circles) can mechanically unfold and refold. The two entropic springs N2B and PEVK are also depicted as unstructured chains. Gray circles represent the repetition of Ig and fibronectin domains (FnIII) in the A- and M-band. b Crystal structure of the rabbit titin segment I65–I70 (pdb: 3B43). This 566 amino acid-long portion of proximal titin is organized in six tandem Ig modules represented in gray. Cysteines are marked by spheres, which are colored according to their position in the Ig secondary structure topology. Cysteines in β-strands B, F and G are shown in yellow, blue and red, respectively. c Scheme of the topology of a typical Ig domain of titin50, which displays the arrangement of the three clustered cysteines CysB, CysF and CysG. CysF and CysG appear in two adjacent β-strands whereas CysB is located in the opposite β-sheet (upper plane)
