Characterization of the Broad-Spectrum Racemase, BsrF, in Vibrio fischeri

L-amino acids are used by all living organisms as the building blocks of proteins and are well characterized, while D-amino acid enantiomers are less common, and their roles are still being elucidated. Broad-spectrum racemases (Bsr), which have been found in several Bacteria and one Archaeon, can catalyze the interconversion of L- and D-isoforms. These Bsrs have a wide range of possible substrates and differ from each other in several ways, such as specific substrates, regulation, use of cofactors, and localization. Additionally, the Bsr-derived D-amino acids have been implicated in a variety of biological roles, including as modifiers of peptidoglycan and as growth substrates. A Bsr was identified in Vibrio fischeri, BsrF, that appears to be localized to the periplasm. The main objective of this study was to determine the substrate range of BsrF for proteinogenic L-amino acids and to explore functional roles for BsrF. BsrF racemized D-Arg, D-Lys, and D-Met from their L-amino acid counterparts and these D-amino acids accumulated in the growth medium during the log growth phase. Further, BsrF racemized L-Leu, L-Gln, and L-Ala, although they were less optimal substrates and their D-enantiomers did not accumulate in growth medium. D-amino acids that are produced by BsrF and integrated into the peptidoglycan, such as D-Met, did not convey protection against an osmotic shock or provide resistance to vancomycin or D-cycloserine, two antibiotics that target peptidoglycan metabolism. However, I found that the catabolism of D-Arg, and specifically its use as a nitrogen source, is dependent on BsrF. I also found, using amino acid auxotrophs, that BsrF is required for growth of an L-Met auxotroph on D-Met, an L-Lys auxotroph on D-Lys, and an L-Leu auxotroph on D-Leu. Additionally, BsrF is sufficient to confer D-Lys utilization in an Escherichia coli L-Lys auxotroph. Through this work, I have expanded upon the existing knowledge of Bsrs, their substrates, and the biological roles of the produced D-amino acids.

Author dc:creator

• Karoline Elizabeth Dittmer (24400109)

• Biology, Genetics
• Biology, Microbiology
• Chemistry, Biochemistry

Statement dc:rights

• In Copyright
• Open Access after 2028-05-01

DOI dc:identifier

https://doi.org/10.25417/uic.32995166.v1

OAI identifier oai:identifier

oai:figshare.com:article/32995166