posted on 2016-02-19, 17:00authored bySung Joon Kim, Manmilan Singh, Aaron Wohlrab, Tsyr-Yan Yu, Gary J. Patti, Robert
D. O’Connor, Michael VanNieuwenhze, Jacob Schaefer
Plusbacin-A3 (pb-A3) is a cyclic lipodepsipeptide
that exhibits antibacterial activity against multidrug-resistant Gram-positive
pathogens. Plusbacin-A3 is thought not to enter the cell
cytoplasm, and its lipophilic isotridecanyl side chain is presumed
to insert into the membrane bilayer, thereby facilitating either lipid
II binding or some form of membrane disruption. Analogues of pb-A3, [2H]pb-A3 and deslipo-pb-A3, were synthesized to test membrane insertion as
a key to the mode of action. [2H]pb-A3 has an
isotopically 2H-labeled isopropyl subunit of the lipid
side chain, and deslipo-pb-A3 is missing
the isotridecanyl side chain. Both analogues have the pb-A3 core structure. The loss of antimicrobial activity in deslipo-pb-A3 showed that the isotridecanyl side chain is crucial
for the mode of action of the drug. However, rotational-echo double-resonance
nuclear magnetic resonance characterization of [2H]pb-A3 bound to [1-13C]glycine-labeled whole cells of Staphylococcus aureus showed that the isotridecanyl side
chain does not insert into the lipid membrane but instead is found
in the staphylococcal cell wall, positioned near the pentaglycyl cross-bridge
of the cell-wall peptidoglycan. Addition of [2H]pb-A3 during the growth of S. aureus resulted
in the accumulation of Park’s nucleotide, consistent with the
inhibition of the transglycosylation step of peptidoglycan biosynthesis.