General chemical structure of an N-acyl homoserine lactone

N-Acyl homoserine lactones (AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing. Quorum sensing is a method of communication between bacteria that enables the coordination of group based behavior based on population density. They signal changes in gene expression, such as switching between the flagella gene and the gene for pili for the development of a biofilm.

[edit] Quorum sensing

[edit] Mechanism

Signaling molecules are produced within the cell and are released into the environment. The resulting concentration of signaling molecules in the environment is dependent upon population density. Once the population density has reached a particular threshold, gene expression can begin. This allows bacteria to coordinate group-based behavior. N-AHL's produced by different bacteria differ in the length of the R-group side chain. Chain lengths vary from 4 to 18 carbon atoms and in the substitution of a carbonyl at the third carbon.^[1]

[edit] Example

One example of the involvement of AHLs in quorum sensing is in the regulation of the bioluminescent protein luciferase in the luminescent bacteria Vibrio fischeri. Similar pathways occur in other luminescent bacteria. In Vibrio fischeri, when the concentration of AHLs exceeds a certain limit, the transcription of the operon luxAB begins. Transcription of the operon results in luminescence due to the expression of LuxA and LuxB, which form a protein known as luciferase. This is an important feature of quorum sensing, as it makes little sense for one cell to waste the energy producing light, as the resulting light will be so faint it will be more or less undetectable. Instead, once the bacterial population has reached a specific size, only then does light production commence.

[edit] Edman degradation

Homoserine lactone is also a product of the proteolytic reaction of cyanogen bromide (CNBR) with a methionine residue in a protein. This reaction is important in protein sequencing, as the Edman degradation process is unable to sequence more than 70 residues at a time.

[edit] History

Homoserine lactones were first discovered at Cornell University. Resident Professor Bonnie Bassler has, since 2002, made several key discoveries regarding bacterial quorum sensing.

[edit] Notes