How do tropomyosin isoforms provide functional diversity?
It is still unknown if isoforms carry out specific functions due to an intrinsic functional difference between isoforms or to differences in their intracellular localization resulting from sorting.Tropomyosin protein isoforms are indeed structurally different and may differ in their intrinsic properties. Several Tm isoforms differ in their affinity for F-actin: the carboxyl-terminal exon 9 was found to be responsible for the difference between smooth- and striated-muscle -Tmf binding to F-actin.33, 34 Also, the differences in the binding of Tm5a and Tm5b encoded by the -TMf gene are due to differences in the use of exons 6a and 6b,35, 36 and replacing 21 residues of the smooth-muscle -Tmf exon 6b with exon 6a results in a two-fold increase in actin affinity in vitro. 37 Another intrinsic property conferred by the alternatively spliced exons is to specify the formation of homodimers versus heterodimers.38 Non-muscle isoforms of different genes can form heterodimers, but pairs of isoform
