The SARS-Cov2 spike protein has a large N-terminal domain, a transmembrane helix and a short C-terminal region. Before the structure of the protein was known, researchers analysed its amino acid sequence using hydropathy plot analysis to predict the position of loops exposed to an aqueous environment because these show as:
A broad peak (>20 residues) of mixed positive and negative hydropathy
A broad peak (>20 residues) of positive hydropathy
A narrow (5-10 residues) of positive hydropathy
A narrow peak (5-10 residues) of negative hydropathy