ECF128

ECF subgroups

ECF128s1 233 ECF128s2 18

ECF proteins

General description: Members of this group are only present in Actinobacteria and have homology to proteins from the original group ECF128 (91.59%).

Anti-σ factor: Members of ECF128 contain a transmembrane protein in +1 of both ECF128s1 and ECF128s2 (ECF128s1: 72.73%, ECF128s2: 75%). These proteins contain a conserved cytoplasmic N-terminal region with no Pfam domain that could serve as AS domain. These putative AS factors bear several extracytoplasmic Pfam domains in ECF128s2, such as a BNR/Asp-box repeat, sortilin and/or YCF48 photosynthesis system II assembly factor, which could serve as sensing domains. Since the BNR/Asp-box is present in neuraminidases, it is possible that putative AS factors of ECF128s2 are sensing degradation products of the cell wall and, therefore, responding to cell wall stress.

Genomic context conservation: Aside from the transmembrane putative AS factor encoded in +1, likewise members of original ECF128, members of new ECF128 contain a membrane protein in -2 and a sortase in -1 of ECF128s1 (87.5%) (Staroń et al., 2009). The transmembrane protein in -2 is present in 75% of the ECFs of ECF128s1, but this value reduces to 16.67% in ECF128s2. Transmembrane proteins encoded in -2 of ECF128s1 are mainly extracytoplasmic, with a short cytoplasmic region in C-terminal unlikely to contain an AS domain. Other conserved domains of members of ECF128 include an ATP-grasp domain in +2 of ECF128s2.

Studied members: One protein of this group, SCO3736 from S. coelicolor (ECF128s1), is the most upregulated protein in a deletion mutant of ppm1, which encodes the donor sugar polyprenol phosphate mannose (PPM), which provides sugars for the extracytoplasmic glycosyltransferases (Huang et al., 2015). ppm1 deletion mutant is more sensitive to antibiotics that target the biosynthesis of the cell wall (Huang et al., 2015). SCO3736 is co-transcribed with the sortase encoded in -1 and the transmembrane protein encoded in -2 (Huang et al., 2015). It is speculated that the sortase attaches to the transmembrane protein to the cell wall (Huang et al., 2015).

Promoter motif conservation: Predicted target promoter motifs are only conserved in ECF128s2, with CCAACC in -35 and GGCGTC in -10.

Summary: In conclusion, ECF128 could be regulated by CAS encoded in +1, which may respond to extracytoplasmic signals related to the synthesis of the cell wall and/or the process of glycosyl transfer.