Catabolite Control Protein A

Front (top) and side (bottom) views of the structure (PDB: 1rzr[1]) of CcpA (green and red) in complex with co-regulator Hpr-Ser46-P (blue) and target (operator) DNA sequence (gold). CcpA binds DNA as a homodimer (green and red monomer chains) in the N-terminal region of the protein. Binding is modulated allosterically by binding of Hpr-Ser46-P (blue) and small molecule ligands (not shown).

Catabolite Control Protein A (CcpA) is a master regulator of carbon metabolism in gram-positive bacteria.[2] It is a member of the LacI/GalR transcription regulator family.[2] In contrast to most LacI/GalR proteins, CcpA is allosterically regulated principally by a protein-protein interaction, rather than a protein-small molecule interaction.[2] CcpA interacts with the phosphorylated form of Hpr[1] and Crh,[3] which is formed when high concentrations of glucose or fructose-1,6-bisphosphate[3] are present in the cell. Interaction of Hpr or Crh modulates the DNA sequence specificity of CcpA, allowing it to bind operator DNA to modulate transcription.[2] Small molecules glucose-6-phosphate and fructose-1,6-bisphosphate are also known allosteric effectors, fine-tuning CcpA function.[4]

Structure

The DNA-binding functional unit of CcpA consists of a homodimer.[2] The N-terminal region of each monomer form a DNA-binding site while the C-terminal portion forms a "regulatory" domain. A short linker connects the N-terminal DNA binding domain and the C-terminal regulatory domain, which partially contacts DNA when bound.[2] The LacI/GalR subfamily can be functionally subdivided based on the presence or absence of a "YxxPxxxAxxL" motif in the liker sequence; CcpA belongs to the subdivision containing this motif.[5] The regulatory domain is further subdivided into a N-terminal and C-terminal subdomain. Small molecule effector binding occurs in the cleft between these subdomains.[4] Binding to phosphorylated Hpr/Crh occurs along the regulatory domain's N-subdomain.[1]

References

1. Schumacher, M. A.; Allen, G. S.; Diel, M.; Seidel, G.; Hillen, W.; Brennan, R. G. (2004). "Structural Basis for Allosteric Control of the Transcription Regulator CcpA by the Phosphoprotein HPr-Ser46-P". Cell. 118 (6): 731–741. doi:10.1016/j.cell.2004.08.027. PMID 15369672. S2CID 8681392.
2. Swint-Kruse, L.; Matthews, K. S. (2009). "Allostery in the LacI/GalR Family: Variations on a Theme". Current Opinion in Microbiology. 12 (2): 129–137. doi:10.1016/j.mib.2009.01.009. PMC 2688824. PMID 19269243.
3. Landmann, J. J.; Busse, R. A.; Latz, J. H.; Singh, K. D.; Stülke, J. R.; Görke, B. (2011). "Crh, the paralogue of the phosphocarrier protein HPr, controls the methylglyoxal bypass of glycolysis in Bacillus subtilis". Molecular Microbiology. 82 (3): 770–787. doi:10.1111/j.1365-2958.2011.07857.x. PMID 21992469.
4. Schumacher, M. A.; Seidel, G.; Hillen, W.; Brennan, R. G. (2007). "Structural Mechanism for the Fine-tuning of CcpA Function by the Small Molecule Effectors Glucose 6-Phosphate and Fructose 1,6-Bisphosphate". Journal of Molecular Biology. 368 (4): 1042–1050. doi:10.1016/j.jmb.2007.02.054. PMID 17376479.
5. Tungtur, S.; Parente, D. J.; Swint-Kruse, L. (2011). "Functionally important positions can comprise the majority of a protein's architecture". Proteins: Structure, Function, and Bioinformatics. 79 (5): 1589–1608. doi:10.1002/prot.22985. PMC 3076786. PMID 21374721.