Fig. 2.
The amino acid sequence and putative transmembrane helices of the R. sphaeroides subunit CcoN of cytochrome cbb3 in the region of the cross-link. (For the full sequence of subunit CcoN, GenBank entry U58092 with six histidine-tag added to the C terminus.) (A) The sequence of the 11,715-Da (D258 to W358) polypeptide resulting from endoproteinase Asp-N cleavage is presented with glutamate 291 highlighted in green and the alternative fragments after double digestion with endoproteinase Asp-N and trypsin are shown. (B) The sizes of the alternative fragments resulting from endoproteinase Lys-C cleavage in the area of S249 to K360 with or without cross-link are shown. The fully conserved amino acids in heme-copper oxidases are highlighted in red (W263, H267, V270, H317, and H318), and the tyrosine residues 311 and 321 are marked with blue. The putative cross-link is indicated between histidine 267 and tyrosine 311 and the cleavage sites of trypsin and endoproteinase Lys-C within the presented sequences are indicated with vertical bars between K288/Q289 and K298/L299.