Two immunoglobulin-like domains of the Z-disc portion of titin interact in a conformation-dependent way with telethonin.

The giant muscle protein titin/connectin plays a crucial role in myofibrillogenesis as a molecular ruler for sarcomeric protein sorting. We describe here that the N-terminal titin immunoglobulin domains Z1 and Z2 interact specifically with telethonin in yeast two-hybrid analysis and protein binding assays. Immunofluorescence with antibodies against the N-terminal region of titin and telethonin detects both proteins at the Z-disc of human myotubes. Longer titin fragments, comprising a serine-proline-rich phosphorylation site and the next domain, do not interact. The interaction of telethonin with titin is therefore conformation-dependent, reflecting a possible phosphorylation regulation during myofibrillogenesis.