The Gs genome contains three ORFs encoding two proteins with 12 heme binding motifs and one with the unprecedented number of 27 heme binding motifs. These proteins can be divided into three-heme units that are homologous to each other within the same protein. These proteins represent a new class of cytochromes c that is characterized by multidomain composition consisting of highly homologous modules and by a mixed type of heme coordination; while in the other known multiheme cytochromes c all hemes are axially coordinated by two histidines.