Fig. 1.

TfcP is a noncanonical cytochrome c. (A) Architectural model of nonpiliated and piliated T4aPM. PilB and PilT associate with PilC in a mutually exclusive manner during extension and retraction, respectively. Bent arrows, incorporation and removal of the major pilin PilA from the pilus base during extension and retraction, respectively. Proteins labeled with single letters have the Pil prefix. Y1_N and Y1_C indicate the N- and C-terminal domains of PilY1, respectively. The color code for the four minor pilins is as in B. (B) Genetic organization of cluster_1 encoding minor pilins, PilY1.1 and TfcP. Locus tags are included Above and gene names within genes. Distances between start and stop codons are shown Above. (C) Domain architecture of TfcP and homologs. Pink, type I signal peptide; red, cytochrome c domain; and brown, C-terminal extension. The cytochrome c signature motif CxxCH and the distal Cys⁹¹ residue are indicated. Numbering of amino acids is according to the unprocessed, full-length TfcP. (D) Sequence alignment of TfcP homologs. Residues are highlighted based on >80% similarity. Domains are indicated using the color code from C. The cytochrome c signature motif CxxCH and the distal Cys⁹¹ residue are indicated. Numbering of amino acids is according to the unprocessed, full-length proteins.