Chasing the structural diversity of the transcription regulator Mycobacterium tuberculosis HigA2

Abstract

Transcription factors are the primary regulators of gene expression and recognize specific DNA sequences under diverse physiological conditions. Although they are vital for many important cellular processes, it remains unclear when and how transcription factors and DNA interact. The antitoxin from a toxin–antitoxin system is an example of negative transcriptional autoregulation: during expression of the cognate toxin it is suppressed through binding to a specific DNA sequence. In the present study, the antitoxin HigA2 from Mycobacterium tuberculosis M37Rv was structurally examined. The crystal structure of M. tuberculosis HigA2 comprises three sections: an N-terminal autocleavage region, an α-helix bundle which contains an HTH motif, and a C-terminal β-lid. The N-terminal region is responsible for toxin binding, but was shown to cleave spontaneously in its absence. The HTH motif performs a key role in DNA binding, with the C-terminal β-lid influencing the interaction by mediating the distance between the motifs. However, M. tuberculosis HigA2 exhibits a unique coordination of the HTH motif and no DNA-binding activity is detected. Three crystal structures of M. tuberculosis HigA2 show a flexible alignment of the HTH motif, which implies that the motif undergoes structural rearrangement to interact with DNA. This study reveals the molecular mechanisms of how transcription factors interact with partner proteins or DNA.

HigA2 (Rv2021c) Is a Transcriptional Regulator with Multiple Regulatory Targets in Mycobacterium tuberculosis

“…Based on previous studies, the antitoxin HigA2 in Mtb acts as a transcriptional regulator with self-cleavage and structural flexibility and may bind DNA through HTH motifs [ 17 ]. Our study found that HigA2 binds within the higB2 gene, and the expression of HigA2 in M. smegmatis resulted in growth inhibition of the bacteria, whereas the toxin HigB2 did not show toxicity.…”

“…Therefore, the HigBA2 system may play a key role in the formation of Mtb persisters. In addition, the protein crystal structure of HigA2 has been resolved and was found to have N-terminal autocleavage activity that spontaneously removes the N-terminal’s 30 amino acids [ 17 ]. Although the three-dimensional protein structure of HigA2 has been characterized, its DNA recognition site has not been identified.…”

Focused Overview of Mycobacterium tuberculosis VapBC Toxin–Antitoxin Systems Regarding Their Structural and Functional Aspects: Including Insights on Biomimetic Peptides

“…The clip structure, consisting of α3 and α4, is connected to the core domain by two flexible stretches that appear as coils. These segments likely confer the necessary flexibility for binding to the antitoxin [ 59 , 60 , 61 ].…”

“…The clip structure, consisting of α3 and α4, is connected to the core domain by two flexible stretches that appear as coils. These segments likely confer the necessary flexibility for binding to the antitoxin [59][60][61]. The VapBC5 complex adopts a hetero-tetrameric arrangement facilitated by a twofold axis within the crystallographic symmetry, thereby establishing a relationship between two hetero-dimeric units (Figure 1B).…”

D-box-binding protein alleviates vascular calcification in rats with chronic kidney disease by activating microRNA-195-5p and downregulating cyclin D1

“…Transcription factors (TFs) act as regulators of gene expression and possess the ability to identify distinct DNA sequences under various physiological circumstances [ 6 ]. They are extensively involved in the VC process.…”