posted on 2020-10-20, 15:37authored byAlexis
J. Apostolos, Julia M. Nelson, José Rogério A. Silva, Jerônimo Lameira, Alecia M. Achimovich, Andreas Gahlmann, Cláudio N. Alves, Marcos M. Pires
Bacterial cell walls contain peptidoglycan
(PG), a scaffold that
provides proper rigidity to resist lysis from internal osmotic pressure
and a barrier to protect cells against external stressors. It consists
of repeating sugar units with a linkage to a stem peptide that becomes
cross-linked by cell wall transpeptidases (TP). While synthetic PG
fragments containing l-lysine in the third position on the
stem peptide are easier to access, those with meso-diaminopimelic acid (m-DAP) pose a severe synthetic
challenge. Herein, we describe a solid phase synthetic scheme based
on widely available building blocks to assemble meso-cystine (m-CYT), which mimics key structural features
of m-DAP. To demonstrate proper mimicry of m-DAP, cell wall probes were synthesized with m-CYT in place of m-DAP and evaluated for their metabolic
processing in live bacterial cells. We found that m-CYT-based cell wall probes were properly processed by TPs in various
bacterial species that endogenously contain m-DAP
in their PG. Additionally, we have used hybrid quantum mechanical/molecular
mechanical (QM/MM) and molecular dynamics (MD) simulations to explore
the influence of m-DAP analogs on the PG cross-linking.
The results showed that the cross-linking mechanism of transpeptidases
occurred through a concerted process. We anticipate that this strategy,
which is based on the use of inexpensive and commercially available
building blocks, can be widely adopted to provide greater accessibility
of PG mimics for m-DAP containing organisms.