Fig. 1: Signal strapping method rationale.

a cartoon view of an AA15 LPMO structure (id:5MSZ)⁸ depicting copper active site. b copper histidine brace active site (L = exogenous ligand, such as water). c cleavage of (SP) from a protein sequence to reveal a free NH₂ group and the N-terminal histidine chelate. d frequency of N-terminal amino acids in Eukarya as a fraction of all sequences for intracellular (filled columns) and secreted (diagonal stripes columns). Black asterisks represent the amino acid commonly found adjacent to the N-terminus. Red asterisks represent the amino acid least likely to be found adjacent to the N-terminus. e ratio of secreted vs. non-secreted N-terminal amino acids as a fraction of all proteins containing that amino acid at the N-terminus. Black asterisks represent the amino acid three to four times more likely to be found adjacent to the N-terminus of a protein with a SP. The amino acid residues were coloured according to the Rasmol “amino” colour scheme. f The signal strapping method steps. InterPro and Pfam logos are obtained from the InterPro website and are freely available under the CC0 public domain license. Source data are provided as a Source Data file.