Sandbox 1
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Structure HighlightsStructure Highlights
The structure of S. aureus protein has a size of 8.9 kDa. Hfq forms a symmetric hexameric ring with a diameter of ~ 65 Å and width of 23 Å. This hexamer has a central hole, doughnut shape like. The protein have a N-terminal alfa helix (α1) in each subunit tracked by five B strands (β1-β5) Hfq contains a sm fold who share conserved amino acids like the aspartic acid 40 and the glycine 34, determining hydrophobic residues present in the Sm1 motif which maintain the highly distorted Sm1 fold. Tyr56 and Tyr63, highly conserved in the Sm2 motif, are fundamental for the interaction between subunits. The glutamine 8 and tyrosine 42 are highly conserved in Hfq proteins due to their role in uracil binding. Since Sm proteins often yield inactive hexameric forms when over-expressed in bacteria (Zaric et al. 2005) and the heptameric form has never been observed in Hfq, it is likely that the hexamer is the thermodynamically more stable form of this fold.
This protein has four solvent exposed regions which possess very different architectures and electrostatic surfaces and varies from one homolog to another.[1] This regions are the proximal face, the distal face, rim and c-terminal tail. The proximal face has a function very important on the protein. It has a polyU sequences who binds in Rho-Independent terminators of sRNAs The distal face binds to diverse A-rich sequences in mRNAs and SRNAs. Studies have demonstrade that an A-rich motif is critical for Hfq-mediated regulation. Rim binds to UA-rich sequences. This kind of bind improve the interaction of the HFQ with the RNAs
Evolutional ConservationEvolutional Conservation
The hfq of different bacteria include an evolutionarily conserved core consisting of amino acid residues 7–66 and has a C terminal tail which diverge significantly in length and sequence[2]. This C terminal tail is associated with the interaction with some sRnas in the protein[1]. Some studies show that this tail is flexible and have disordered regions which can facilitate intermolecular interactions. This disorder appears to provide a moiety who act like a bridge connecting diverse RNA molecules that could be followed by stable accommodation of the substrate at the distal site at the poliA binding motifs.[2]