Figure 5.

Diversity of surface proteins. Consistent with the unique ability of M. acetivorans among the archaea to form complex multicellular structures, a large number and diverse array of surface proteins were identified. Illustrated are examples of domain architectures that contain β-propeller, polycystic kidney disease (PKD), and β-helix domains. The PKD and YVTN β-domains share sequence similarity to metazoan cell-adhesion molecules, suggesting a role for these proteins in the formation of multicellular structures. The domains were identified by similarity to structurally defined domains in M. mazei surface antigens (H. Jing, in prep.). The helical transmembrane regions (HTM) were predicted using PHDhtm (Rost et al. 1996). The Ca²⁺-binding β-hairpin motifs were predicted based on sequence similarity with a previously identified Ca²⁺-binding motif (Springer et al. 2000). One β-propeller domain appears intermediate between YVTN and WD40 β-propellers.