5 0 K D ▁mole cular ▁weight ▁— ▁a ▁protein ▁whose ▁existence ▁has ▁been ▁known ▁since ▁the ▁ 1 9 8 0 s . ▁Trans lation ▁of ▁the ▁extra ▁ex on ▁causes ▁a ▁ 6 8 - ▁to ▁ 7 9 - am ino ▁acid ▁acid - rich ▁insert ▁between ▁hel ices ▁I ▁and ▁II ▁within ▁the ▁C - term inal ▁tail ▁domain . ▁Mut ations ▁within ▁the ▁insert ▁region ▁correlate ▁with ▁her edit ary ▁id iop ath ic ▁dil ated ▁card iom y op ath y . ▁ ▁The ▁length ▁of ▁the ▁insert ▁in ▁met av in cul in ▁is ▁ 6 8 ▁AA ▁in ▁m amm als ▁and ▁ 7 9 ▁in ▁f rog . ▁Comp ared ▁met av in cul in ▁sequences ▁from ▁p ig , ▁man , ▁ch icken , ▁and ▁f rog , ▁and ▁found ▁the ▁insert ▁to ▁be ▁b ipart ite : ▁the ▁first ▁part ▁variable ▁and ▁the ▁second ▁highly ▁conser ved . ▁Both ▁vin cul in ▁is o forms ▁co - local ize ▁in ▁mus cular ▁ad hes ive ▁structures , ▁such ▁as ▁dense ▁pla ques ▁in ▁smooth ▁mus cles , ▁inter cal ated ▁disc s ▁in ▁card iom y ocy tes , ▁and ▁cost amer es ▁in ▁ske let al ▁mus cles . ▁Met av in cul in ▁tail ▁domain ▁has ▁a ▁lower ▁aff inity ▁for ▁the ▁head ▁as ▁compared ▁with ▁the ▁vin cul in ▁tail . ▁In ▁case ▁of ▁met av in cul in , ▁un fur ling ▁of ▁the ▁C - term inal