A new fold in TANGO1 evolved from SH3 domains for the export of bulky cargos

Bulky cargos like procollagens, apolipoproteins, and mucins exceed the size of conventional COPII vesicles. During evolution a process emerged in metazoans, predominantly governed by the TANGO1 protein family, that organizes cargo at the exit sites of the endoplasmic reticulum and facilitates export by the formation of tunnel-like connections between the ER and Golgi. Cargorecognition appears to be mediated by an SH3-like domain, however, just how the vastly different cargos are recognized remains elusive. Based on structural and dynamic data as well as interaction studies from NMR spectroscopy presented here, we show that the luminal cargo-recognition domain of TANGO1 adopts a new functional fold for which we suggest the term MOTH (MIA, Otoraplin, TALI/TANGO1 homology) domain. Also, differences in the structural properties within the domain family suggest fundamentally different mechanisms of cargo-recognition in vertebrates and invertebrates. Similarly, in vertebrates, it is proposed that cargo-specificity is mediated by structural differences within the vertebrate TANGO1 and TALI MOTH domains themselves.