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Microbes & Immunity Brachyspira pilosicoli novel outer membrane proteins

C-terminal β-barrel domain of poly-β-1,6-N-acetyl-D- match with the bacterial polysaccharide OM secretin of E.
glucosamine (PNAG) export protein PgaA of E. coli K-12 coli K-12, further supporting involvement of this protein
(PDB ID: 4Y25) (Tables 2 and S3). E. coli PgaA comprises in secretion. Complementing this, PANNZER annotated
a 16-stranded β-barrel domain at the C-terminal and BP951000_RS10215 as VspD, which, in B. hyodysenteriae,
eight periplasmic tetratricopeptide repeats (TPRs) is associated with adhesion and virulence. Together, these
at the N-terminal. In contrast, BP951000_RS10215 findings suggest a dual role for the protein in secretion
lacks periplasmic TPR domains. PgaA facilitates the and adhesion. (Tables 2 and S3). Among nine strains of
translocation of PNAG polymer from the periplasm to B. pilosicoli, BP951000_RS04760 exhibited 260 amino
the cell surface, a key step in biofilm formation. 66-68 The acid substitutions and multiple deletions, indicating high
structural similarity of β-barrels between E. coli PgaA variability (Table S5). These variations were distributed
and BP951000_RS10215 implies a possible role of the throughout the protein (Figure 2C).
Brachyspiral protein in translocation. Consistently, the
Foldseek tool identified its closest match with the bacterial 3.2.1.4. BP951000_RS01125
polysaccharide OM secretion of E. coli K-12, supporting a BP951000_RS01125 is annotated as the curli production
potential role in polysaccharide secretion. assembly/transport component CsgG in both the NCBI
and UniProt databases. SignalP predicted a lipoprotein
In parallel, PANNZER annotated BP951000_RS10215
as VspB, suggesting a possible involvement in surface signal peptide, whereas LipoP predicted it as a cytoplasmic
protein. The structural model of the protein showed a
antigenic variation. Together, these findings suggest
a possible dual function in secretion with surface β-barrel architecture comprising eight β-strands extending
variability (Tables 2 and S2). Given its high sequence and into the periplasm via the periplasmic domain (Figure 2D).
structural homology with B. hyodysenteriae, there is a DALI server results showed that BP951000_RS01125
strong likelihood that BP951000_RS10215 plays a role in exhibited the best structural match with OmpF (PDB
adherence and host colonization. 62-64 Sequence variation ID: 4RLC) of Pseudomonas aeruginosa (Tables 2 and S3).
analysis across nine strains of B. pilosicoli revealed 208 P. aeruginosa OmpF is involved in biofilm formation, OM
amino acid substitutions and several deletions (Table S5). vesicle production, adhesion, and host immune system
75-81
These variations are distributed throughout the protein modulation. The Foldseek tool identified its closest
(Figure 2B), suggesting the ability of B. pilosicoli to structural match with an uncharacterized protein from the
marine metagenome. Sequence-based annotation using
rapidly adapt to changing environments or host immune
responses. 62 PANNZER and eggNOG-mapper confirmed BP951000_
RS01125 to be a CsgG homolog (Tables 2 and S3).
3.2.1.3. BP951000_RS04760 The CsgG curli production assembly/transport
BP951000_RS04760 is annotated as VspD in the UniProt component OMP is essential for the secretion of curli—
database and as a variable surface family protein in functional amyloid fibers that constitute the primary
NCBI. As discussed in Section 3.2.2, Vsps are involved in protein component of biofilm extracellular matrices in
bacterial attachment to host cells. B. hyodysenteriae VspD Bacteroidetes and Proteobacteria—and play key roles in
64
is a virulence factor and a potential vaccine development pathogenesis. Curli fimbriae are involved in the initial
82
target. Our predictions revealed that BP951000_RS04760 colonization of the host, as well as in bacterial persistence
69
carries a signal peptide and comprises a 16-stranded and invasion. 83-85 Considering that both OmpF and CsgG
β-barrel architecture, with varying strand lengths creating are functionally linked to surface-associated processes
an elliptical barrel surface on the extracellular side and virulence, the combined structural and sequence-
(Figure 2C). The protein showed the closest structural match level analyses strongly suggest that BP951000_RS01125
with the β-barrel domain of the cellulose synthase operon may play a similar role in B. pilosicoli. Across B. pilosicoli
protein C (BcsC porin; PDB ID: 6TZK) from E. coli K-12 strains, BP951000_RS01125 exhibited sequence variations
(Tables 2 and S3), as determined using the DALI server. at five positions (S63, D79, T190, I210, and L380)
BcsC is a 16-stranded β-barrel protein with a periplasmic (Tables 3 and S4). Structural mapping revealed that L380 is
domain consisting of 19 TPRs, which facilitate the secretion located within the β-barrel domain, whereas the remaining
of phosphoethanolamine-cellulose across the OM. 70-74 In variations are positioned in the periplasmic region of the
contrast, BP951000_RS04760 lacks TPRs. The structural protein (Table S4).
homology between the β-barrel domains of E. coli BcsC and
BP951000_RS04760 implies a possible role for BP951000_ 3.2.1.5. BP951000_RS03440
RS04760 in translocation. This structural insight is BP951000_RS03440 is annotated as a hypothetical protein
reinforced by the Foldseek tool, which identified its closest in the UniProt database, whereas NCBI identifies it as an

Volume 2 Issue 4 (2025) 91 doi: 10.36922/MI025230050