Does a Conjugation Site Affect Transport of Vitamin B₁₂–Peptide Nucleic Acid Conjugates into Bacterial Cells?

Abstract

Gram‐negative bacteria develop specific systems for the uptake of scarce nutrients, including vitamin B12. These uptake pathways may be utilized for the delivery of biologically relevant molecules into cells. Indeed, it was recently reported that vitamin B12 transported an antisense peptide nucleic acid (PNA) into Escherichia coli and Salmonella Typhimurium cells. The present studies indicate that the conjugation site of PNA to vitamin B12 has an impact on PNA transport into bacterial cells. Toward this end, a specifically designed PNA oligomer has been tethered at various positions of vitamin B12 (central Co, R5′‐OH, c and e amide chains, meso position, and at the hydroxy group of cobinamide) by using known or newly developed methodologies and tested for the uptake of the synthesized conjugates by E. coli. Compounds in which the PNA oligonucleotide was anchored at the R5′‐OH position were transported more efficiently than that of other compounds tethered at the peripheral positions around the corrin ring. Of importance is the fact that, contrary to mammalian organisms, E. coli also takes up cobinamide, which is an incomplete corrinoid. This selectivity opens up ways to fight bacterial infections.

Antibacterial Peptide Nucleic Acids—Facts and Perspectives

“…Furthermore, we have shown that vitamin B 12 acts as a carrier of PNA to E. coli and Salmonella enterica subsp. enterica serovar Typhimurium [119,125]. These studies indicate that vitamin B 12 could be a good candidate for a PNA transporter into bacteria.…”

Extracellular loops of BtuB facilitate transport of vitamin B12 through the outer membrane of E. coli

“…The TBDTs can be also hijacked by colicins [5], bacteriophages [6], and sideromycins [7] to enter the bacterial cells. Recently, we have shown that vitamin B 12 delivers peptide nucleic acid and 2'O-methyl RNA oligomers into E. coli and S. Typhimurium cells [8][9][10][11]. Thus, vitamin B 12 may be used as a carrier of various oligonucleotides to bacterial cells.…”

Inhibition of Escherichia coli Growth by Vitamin B12–Peptide Nucleic Acid Conjugates

“…Previously, we investigated the ability of the natural noncationic carrier vitamin B 12 to transport PNA oligomers into E. coli cells. 20,26 Encouraged by the observation that conjugation of vitamin B 12 transports PNA to E. coli cells, we now tested the antibacterial potential of such conjugates using a PNA sequence with antibacterial properties, namely, the PNA aimed to target the mRNA transcript of an essential gene. Such PNA, targeting the expression of an essential protein, should inhibit bacterial growth provided that it is delivered to the cell interior and bound to the target at required concentrations.…”

“…It is not harmful for humans, cannot be overdosed, and does not induce resistance in bacteria. Moreover, vitamin B 12 can be chemically modified just in few steps with high synthetic efficacy; the conjugation procedure is simple and high yielding. , Furthermore, some derivatives of vitamin B 12 (e.g., derivatives of cobyric acid and cobinamide) are specifically recognized by bacteria, and not by mammalian cells, so they can be applied directly to bacterial cells. , Undeniably, the natural uptake properties of vitamin B 12 in different bacteria still need to be further researched; however, all the above should make vitamin B 12 , at least in principle, a better transporter of antisense PNAs in terms of further medical use.…”