Curli


The Curli protein is a type of amyloid fiber produced by certain strains of enterobacteria. They are extracellular fibers located on bacteria such as E.coli and Salmonella. These fibers serve to promote cell community behavior through biofilm formation in the extracellular matrix. Amyloid is associated with human neurodegenerative diseases such as Alzheimer's disease. The study of curli may help to understand human diseases thought to arise from improper amyloid fiber formation.

Gene regulation

CsgD is a positive transcriptional regulator of the csgBA operon. The CsgD protein is the transcription regulator and positively regulates the csgBA operon but shockingly does not regulate its own expression. The csgBA operon encodes the major structural subunit of curli, CsgA, as well as the nucleator protein CsgB. Further research still needs to be conducted in order to see what stimulates CsgD expression or activity but some evidence supports that the activation of the protein is caused by the phosphorylation of an aspartic acid residue of the N-terminal receiver domain. Since CsgD must be present for csgBA promoter activity, it is therefore shown that regulators of CsgD expression also influence the expression of csgBA.
Many environmental cues play a role in Curli gene expression. Growth at a temperature below 30 degrees celsius promotes Curli gene expression. Additionally, when there is a lack of salt and nutrients such as nitrogen, phosphate and iron, Curli gene expression is stimulated.