Lipoteichoic acid (LTA) is an important component of the cell envelope of various Gram-positive
bacteria. In Staphylococcus aureus it consists of a polyglycerolphosphate chain that is decorated
with D-alanine esters and anchored to the cell membrane via a glycolipid. The lack of D-alanine
modifications leads to increased susceptibility to cationic antimicrobial peptides and the complete
absence of LTA results in aberrant positioning of septa, enlargement of cells and eventual cell
lysis, indicating a link between LTA synthesis and cell division. Although key enzymes required for
LTA synthesis and D-alanylation have been identified, the full process has not been elucidated and
is investigated in this study.
Using a bacterial two-hybrid approach it was shown that the three key LTA synthesis enzymes, YpfP,
LtaA and LtaS, interact with one another, indicating the formation of a multi-enzyme complex. In
addition, these three proteins interacted with numerous cell division and peptidoglycan synthesis
proteins. Fluorescence microscopy studies indicated that YpfP and LtaA localise to the membrane,
while LtaS appeared to accumulate at the site of cell division in cells with fully formed septa.
Together, these data provide further experimental evidence for the coordination between the
processes of cell division and LTA synthesis.
Four proteins, DltA-D, are essential for the D-alanylation of LTA. The mechanism begins with DltA
transferring D-alanines onto the carrier protein DltC. However, Fischer and colleagues, and Neuhaus
and Baddiley have proposed two conflicting models for the remainder of the mechanism for
D-alanylation. Here, using a cellular protein localisation analysis it was shown that DltC does not
traverse the membrane and membrane topology studies indicated that DltD is anchored to the outside
of the cell, contrary to the Neuhaus and Baddiley model. In summary, the data presented in this
study are in support of the D-alanine substitution model proposed by
Werner Fischer.