A SURVEY OF THE PRIMARY STRUCTURE AND THE INTERSPECIES CONSERVATION OF I-BAND TITINS ELASTIC ELEMENTS IN VERTEBRATES

Titin is a >3000-kDa large filamentous protein of vertebrate-striated muscle, and single titin molecules extend from the Z disc to the M lin e. In its I-band section, titin behaves extensible and is responsible for myofibrillar passive tension during stretch. However; details of t he molecular basis of titin's elasticity are not known. We have compar ed the motif sequences of titin elastic elements from different verteb rate species and from different regions of the molecule. The I-band ti tin Ig repeats that are expressed in the stiff cardiac muscle and thos e that are tissue-specifically expressed in more elastic skeletal musc les represent distinct subgroups. Within the tissue-specifically expre ssed Ig repeats, a super-repeat structure is found. For the PEVK titin sequences, we surveyed interspecies conservation by hybridization exp eriments. The sequences of the titin gene which code for the C-termina l region of the PEVK domain are conserved in the genomes of a larger v ariety of vertebrate, whereas the N-terminal PEVK sequences are more d ivergent. Future comparisons of titin gene sequences from different ve rtebrates may improve our understanding of how titin contributes to sp ecies diversity of myofibrillar elasticity. Within one species, differ ent classes of Ig repeat families may contribute to elastic diversity of the titin spring in different segments. (C) 1998 Academic Press.