D-alanylation? What?

Question

Hey, back again. Need to make sense of the following sentence:

"[...] GAS harbors a genetic locus with homology to the four-gene D-alanyl-LTA (dltABCD) operons first described in the model gram-positive orangisms [...]"

what is "four-gene D-alanyl-LTA (dltABCD) operons"?

(I know that LTA is lipoteichoic acid, a component of gram-positive bacterial cell walls), but I dont really understand what operons are, or what four-gene is, or what D-alanyl-LTA is supposed to be.. oh my gosh.

And I'm searching the web for definitions/descriptions/anything on D-alanylation, D-alanyl, D-alanine, D-alanine-D-alanyl carrier protein ligase, and I feel like I'm going in circles, and I'm just getting so frustrated. If you could sort this out for me with detailed descriptions, I would love you to death.

Answer 1

This question is somewhat confusing to me as well,   and i am not incredibly familiar with microbiology  but may beable to give insight to some loose ends.  

first off,   an operon is essentially a genetic circuitry/pathway-mechanism  which involves the presence of some substance within the cell,   possibly of nutritional or accessory nature which regulates genetic transcription.

So thus,  if for instance a certain sugar is being uptaken by a bacteria, or a amino acid analogue in this case (d-alanyl-LTA),  then that may activate or deactivate transcribable regions of the DNA via interactions with  transcription factors and accessory proteins which may aid in mRNA synthesis.    

A classic example of the operon is the LAC operon or LAC Z operon,   in which different enzymes will be actively transcribed or turned off based on the concentration of Lactose in the cell.  

In the case of the operon i do believe their are four genes involved,  i do not know if this is the criteria for operons or not however.  I am not really understanding the whole question which you are given,  if it is only a part of a bigger question or in a sequence of questions. I am not very familiar with gram + biosynthesis of their wall.  

I think the question, whatever it may be addressing,  is more focused on the idea of operon and your understanding of the basic pathway which operons follow,  not so much the specifics of this particular one.  

Answer 2

Having briefly skimmed the article mentioned, it seems that dlt operon encodes D-alanylation (incorporates D-alanine into the teichoic acids on the cell surface (quoted in the Discussion)). This modification results in an increase in positive surface charge, which in turns increases resistance to AMP.. It's all in the Discussion, babe.