Previously, we cloned two Branchiostoma IF proteins A3 and B2 and demonstrated that both can form heteropolymeric IF based on a coiled coil dimer consisting of one B2 and one A3 polypeptide. In this study we continued in the characterisation of the B2/A3 heterodimer by searching for the sequences that play an important role in the triggering of the B2/A3 heterodimer. Using a series of deletion and chimeric B2, A3 and B1 constructs and the overlay assay as a tool, we were able to identify a part of the B2 sequence (segment 1A, linker L1 and the N-terminal part of segment 1B) which retains the ability of the full length protein B2 to specifically recognize A3 in blot overlays. Moreover, inspection of this A3-competent B2 fragment identified a short sequence in segment 1B which shares with the currently known trigger-like motif of cortexillin and other coiled coil proteins potential to form multiple inter-chain ionic interactions. Thus, a common and essential feature of trigger sequences with different primary structures found so far in IF and other coiled coil proteins seems to be their ability to form multiple inter-chain ionic interactions which brings the chains close to one another and allows coiled coil formation to propagate accordingly.
Amino Acid Motifs Amino Acid Sequence