Titin: a molecular control freak.

Recent studies of the giant protein titin have shed light on its roles in muscle assembly and elasticity and include the surprising findings described here. We now know that the titin kinase domain, which has long been a puzzle, has a novel regulation mechanism. A substrate, telethonin, has been identified that is located over one micron away from the kinase domain in mature muscle. Single-molecule studies have demonstrated the fascinating process of reversible mechanical unfolding of titin. Lastly, and most surprisingly, it has been claimed that titin controls assembly and elasticity in chromosomes.