Local Variability in the Mechanics of Titin’s Tandem Ig Segments*

The functionally elastic, I-band part of the myofibrillar protein titin (connectin) contains differentially expressed arrays of serially linked immunoglobulin (Ig)-like domains, the length and composition of which vary among the titin isoforms. The biological rationale of the differential expression as well as the contribution of the Ig domain mechanical characteristics to the overall mechanical behavior of titin are not exactly known. The paper briefly reviews the relevant works that have addressed the Ig-domain mechanics problems and presents the authors’ experimental approach to studying the mechanical behavior of Ig domains. The mechanics of an eight domain segment from the differentially expressed tandem Ig region of titin (I55-62) was studied with an atomic force microscope specially used for stretching single molecules, and the results were compared to known mechanical properties of other domains and segments.