Abstract
The bacterial cell wall is an important and highly complex structure that is essential for bacterial growth because it protects bacteria from cell lysis and environmental insults. A typical Gram-positive bacterial cell wall is composed of peptidoglycan and the secondary cell wall polymers, wall teichoic acid (WTA) and lipoteichoic acid (LTA). In many Gram-positive bacteria, LTA is a polyglycerol-phosphate chain that is decorated with d-alanine and sugar residues. However, the function of and proteins responsible for the glycosylation of LTA are either unknown or not well-characterized. Here, using bioinformatics, genetic, and NMR spectroscopy approaches, we found that the Bacillus subtilis csbB and yfhO genes are essential for LTA glycosylation. Interestingly, the Listeria monocytogenes gene lmo1079, which encodes a YfhO homolog, was not required for LTA glycosylation, but instead was essential for WTA glycosylation. LTA is polymerized on the outside of the cell and hence can only be glycosylated extracellularly. Based on the similarity of the genes coding for YfhO homologs that are required in B. subtilis for LTA glycosylation or in L. monocytogenes for WTA glycosylation, we hypothesize that WTA glycosylation might also occur extracellularly in Listeria species. Finally, we discovered that in L. monocytogenes, lmo0626 (gtlB) was required for LTA glycosylation, indicating that the encoded protein has a function similar to that of YfhO, although the proteins are not homologous. Together, our results enable us to propose an updated model for LTA glycosylation and also indicate that glycosylation of WTA might occur through two different mechanisms in Gram-positive bacteria.
Highlights
The bacterial cell wall is an important and highly complex structure that is essential for bacterial growth because it protects bacteria from cell lysis and environmental insults
Based on the similarity of the genes coding for YfhO homologs that are required in B. subtilis for lipoteichoic acid (LTA) glycosylation or in L. monocytogenes for wall teichoic acid (WTA) glycosylation, we hypothesize that WTA glycosylation might occur extracellularly in Listeria species
To identify proteins required for LTA glycosylation in B. subtilis, the L. monocytogenes GtlA protein sequence was used as a query sequence in a BLASTP search against the B. subtilis 168 genome
Summary
The bacterial cell wall is an important and highly complex structure that is essential for bacterial growth because it protects bacteria from cell lysis and environmental insults. The Listeria monocytogenes gene lmo1079, which encodes a YfhO homolog, was not required for LTA glycosylation, but instead was essential for WTA glycosylation. GtlA (locus tag Lmo0933 in strain EGD-e) has been identified as the putative cytoplasmic GT involved in the glycosylation process of LTA in the L. monocytogenes strain 10403S [29], biochemical evidence for such an activity is still lacking. This protein is anchored by two C-terminal transmembrane helices to the membrane and contains a large N-terminal cytoplasmic enzymatic domain. Did we discover additional genes required for LTA glycosylation, but the work allowed us to propose an alternative, extracellular, glycosylation mechanism for wall teichoic acid
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