Fig. 1: Proteomic analysis of the binding partners of the cytoplasmic tail of SARS-CoV-2 S protein.

a Mass spectrometry analysis from affinity chromatography of 293T cell lysates using GST-S tail (1237–1273). The plot compares the average spectral counts from three independent replicates of GST-S(1237–1273) versus the negative control (GST). Values are in Supplementary Data 1. b Volcano plot comparing the spectral intensities from proteins bound to GST-S(1237–1273) or GST alone, using data from three independent experiments. c Immunoblots of eluates from the indicated GST-tagged S tails prepared as in (a). Coomassie blue stained gels show the GST-tail fusions with adjacent residues of the tail of S (residues 1237–1273) mutated to alanine. The blots shown are representative from two independent experiments, and the input lysate represents 1/100 of the material applied to the GST fusions. d Validation of the interactions using two distinct halves of the tail of S: the membrane-proximal half (residues 1237–1254) and the distal half (residues 1255–1273). The blots shown are representative from three independent experiments. Binding of COPII is seen to residues 1237–1254 but this could be spurious—this region contains eight cysteines, and only one charged residue and so could be sticky in the absence of the rest of the tail and thus binds COPII non-specifically. In the context of the entire tail, none of the double alanine mutations in this region reduces substantially COPII binding, in contrast to what is seen with SNX27. e Schematic of the transmembrane and cytoplasmic domain of the SARS-CoV-2 S protein. The residues that are critical for binding to the different cytoplasmic factors are indicated.