Proteins of the Thermophilic Fungus Humicola lanuginosa

Two eukaryotic cytochrome c components, ca and cb, were purified from the thermophilic fungus Humicola lanuginosa. These proteins appear to differ only in the degree of methylation of lysyl amino groups. The ca component is the first cytochrome c of fungal origin found to contain 2 residues of methylated lysine. The complete amino acid sequence of H. lanuginosa cytochrome ca, the major component, was established. The protein consists of a single polypeptide chain of 111 residues. On alignment with vertebrate cytochromes c, the peptide chain extends for 8 residues at the amino-terminal end. As with other fungal cytochromes c of known sequence, residue 104 is deleted. Considering the region of residues 1 through 103, H. lanuginosa cytochrome ca most closely resembles the primary structure of Neurospora crassa cytochrome c. The two proteins show 18 differences. H. lanuginosa cytochrome ca contains a phenylalanyl residue at position 74. Other cytochromes c of known sequence contain a constant segment from residues 70 to 80, with a tyrosyl residue situated at position 74.