Vitamin B12 transporter BtuB (BtuB)

BtuB (Vitamin B12 transporter BtuB) is a 22-stranded beta-barrel protein located in the outer membrane of Gram-negative bacteria, most notably Escherichia coli. Its primary biological function is the high-affinity binding and active translocation of vitamin B12 (cobalamin) from the extracellular environment into the periplasmic space, a process that is strictly dependent on calcium ions and energized by the TonB-ExbB-ExbD complex. Beyond its role in nutrient acquisition, BtuB serves as a critical receptor for various lethal agents, including E-type colicins and bacteriophages such as BF23, which hijack the transporter to gain entry into the cell. In the field of drug development, BtuB is a significant target for "Trojan horse" antimicrobial strategies. Researchers are exploring the conjugation of antibiotics or antisense oligonucleotides, such as peptide nucleic acids (PNAs), to vitamin B12 to facilitate their uptake through the BtuB pathway, thereby bypassing the restrictive outer membrane barrier of resistant bacteria. While this approach offers high specificity, therapeutic challenges include the rapid emergence of resistance through receptor mutations and the potential for off-target effects on the host's beneficial microbiome.

Other names

Cobalamin receptorOuter membrane cobalamin translocatorBfeCerDcrC

BtuB facilitates the active translocation of vitamin B12 across the bacterial outer membrane using energy derived from the TonB-ExbB-ExbD complex. It is also utilized as a gateway for the delivery of antimicrobial conjugates (e.g., B12-PNA) and the entry of colicins and bacteriophages.