Adenosylcobalamin riboswitch (AdoCbl riboswitch)

The Adenosylcobalamin riboswitch is a highly structured non-coding RNA element located in the 5' untranslated region (UTR) of various bacterial mRNAs [1, 2]. It serves as a critical genetic control element that regulates the biosynthesis and transport of vitamin B12 by directly sensing intracellular levels of adenosylcobalamin (AdoCbl), the coenzyme form of the vitamin [2, 3]. When AdoCbl binds to the riboswitch's aptamer domain, it triggers an allosteric conformational change in the downstream expression platform [2, 4]. This structural shift leads to the suppression of gene expression through mechanisms such as transcriptional attenuation or the inhibition of translation initiation by sequestering the ribosome-binding site [1, 2]. This feedback loop is essential for maintaining metabolic homeostasis in many bacteria, including significant human pathogens like Salmonella typhimurium and Escherichia coli [1, 4]. Because these riboswitches are widely distributed in the bacterial kingdom but absent in human cells, they are considered promising targets for the development of novel, narrow-spectrum antibacterial agents [4, 5]. Targeting the riboswitch with synthetic cobalamin analogs can potentially disrupt essential bacterial processes, offering a strategy to combat antibiotic resistance [5].

Other names

Coenzyme B12 riboswitchCobalamin riboswitchClass I cobalamin riboswitchCbl-I riboswitchbtuB leader RNAB12-responsive element

The mechanism involves the direct binding of adenosylcobalamin to the aptamer domain of the riboswitch, which induces an allosteric conformational change in the expression platform of the mRNA [1, 2]. This structural rearrangement typically results in the formation of a transcriptional terminator or the sequestration of the ribosome-binding site, thereby inhibiting the expression of genes involved in cobalamin transport and biosynthesis [1, 3].