Streptococcus pneumoniae is a gram-positive bacterium and a common coloniser of the human airway. S. pneumoniae can also become pathogenic, causing infections such as sepsis and pneumonia. During infections, S. pneumoniae can metabolise sialic acid, a carbohydrate attached to most mammalian cell surfaces, as a carbon source and for immune evasion, which is common across most pathogenic bacteria1. This makes the bacterial pathways involved in sialic acid metabolism an important topic for antibacterial research2. Most proteins involved in sialic acid transport and metabolism are located in the nan operon of the S. pneumoniae genome2. The operon is regulated by the transcription factor SpNanR. Our research group has recently solved the three-dimensional structure of SpNanR bound to its DNA recognition promoter sequence, the nanE promoter, and has demonstrated that SpNanR functions as a dimer, binding to two palindromic half sites in the nanE promoter. How SpNanR recognises and engages its promoter DNA sequence remains unknown. Based on three-dimensional crystal structure, amino acids in SpNanR were individually substituted and nucleotides in the DNA recognition sequence were mutated to probe the interactions between SpNanR and DNA.
Our results show that some SpNanR amino acid substitutions impacted the interaction between SpNanR and DNA. However, the various amino acid substitutions had very different degrees of impact on the interaction. All the mutated DNA base pairs had significantly decreased binding affinity for wild-type SpNanR. My poster will present these results and explain how these experiments help us understand more about the molecular interaction between the SpNanR transcriptional regulator and its DNA recognition sequence.