Dear Natalia,

what realy makes the G143A mutation so important is the structural change that it confers. It has very litle to do with the chemical properties of the 2 aminoacids. Alanine is "bigger" than Glycine because it has an additional methyl group. It seems that this difference is enough to keep strobilurins from binding to the cytochrome b Qo site rendering them ineffective. Imagine a small thorn (CH3 group) in a key-hole which hinders the key from entering. One the other hand, this minor change in the Qo cavity does not affect ubiquinone from binding and so the electron transport chain is not negatively affected. For more details see "Re-examination of inhibitor resistance conferred by Qo-site mutations in cytochrome b using yeast as a model system" by Fisher, N., Meunier, B. (2005) Pest Management Science, 61 (10), pp. 973-978.

I hope I helped a little.

Best Regards

Anastasios

Before i will touch the mutation, How the Qq Fungicides work.

The Qol fungicides are respiration inhibitors - their fungicidal activity comes from their ability to inhibit mitochondrial respiration by binding at the so-called Qo site (the outer quinol- oxidation site or ubiquinol site) of the cytochrome bc, enzyme complex (complex III), located in the inner mitochondrial membrane of fungi and other eukaryotes. This inhibition blocks electron transfer between cytochrome b and cytochrome c which, in turn, leads to an energy deficiency in fungal cells that halts reduced NADH oxidation and ATP synthesis, thereby preventing the production of ATP. This leads to the stopping of energy production and the fungus will eventually die. All the Qol fungicides share this common mode of action.

There are 3 mutations which are responsible for fungicide resistance. The base is point mutation. It is interaction studies which have shown owing to which they bypass the Qq1 site specificuty

Indeed the G143A mutation is very common in phytopathogenic fungi leading to QoI resistance.

thank you for your questions !! but I want to know why the change of one amino acid causes this. My question is oriented to the chemical characteristics the amino acid, what are the important diferences (chemical) in this amino acid to produce this mutation.

pd: Sorry for my english.

I don't know the chemical reason. Generally target site modifcations impact on fungcide affinity, but in the cas of strobilurins-cyt b I have not made the literature analyses.

"In susceptible strains, the glycine in position 143

probably contributes to the binding of the benzene ring

linker of strobilurin fungicides to the Qo site of cytochrome

b" extract from Leroux & Walker, 2010 (Applied Env. Microbiologie). You propbably need to read the chemical literature related to strobilurins. Are there any structural models published? If not you may also find some indications and contacts on the FRAC website http://frac.info/. Good luck, Sabine

Dear Natalia,

If you download the paper of Grasso V, et al., Pest Manag Sci. 2006 Jun;62(6):465-72,

you can read that the codon GGT at position 143 is located exactly at the exon/intron boundary and is likely part of the signal sequences essential for the recognition of the intronic RNA to be excised. A nucleotide substitution in codon 143 (GGT → GCT), which is two nucleotides upstream from the exon/intron junction, will strongly affect the splicing process, leading to a deficient cytochrome b.

best regards

thank you Salvatore Dimonte for your answer :D

It should be noted that the paper by Grasso et al. is about some organisms that contain an intron near this site. Many fungi do not and this has been hypothesized as one reason some fungi develop resistance to QoIs quickly while other fungi do not (e.g. Vallières et al. 2011. Appl. Environ. Microbiol. 77:2088-2093).

Gisi et al. 2002. Pest Manag Sci 58:859–867 is a good review of mechanisms of QoI resistance and has nice diagram of the binding pocket of the bc complex that you might find helpful.

Thank you Linda

Dear Natalia,

I don't know if it would be useful in your particular case, but my research group have developed a bioinformatic tool called MOSST that is able to predict with good accuracy the effects of mutations in proteins, based on evolutionary and philogenetic information about the conservation of physicochemical properties in proteins, derived from the primary sequence of a given protein and its homologous (paralogous and orthologous) proteins. We have applied this approach to the study and prediction of disease causing mutations in vivo, and also to the rational design of protein mutations in the frame of a protein engineering strategy.

We are currently working on the incorporation of other information (structural, interaction, metabolic, etc.) to strengthen the prediction accuracy of our tool.

We are always looking for new applications of our methodology and protein mutation examples where we could test our predictions, with the final goal of improving the accuracy of our method. If you are interested to use this approach, please contact me and I can give you the directions to apply MOSST to your protein or even better, I could do part of the analysis and discuss the results with you.

Best regards,

Alvaro

Dear Natalia,

what realy makes the G143A mutation so important is the structural change that it confers. It has very litle to do with the chemical properties of the 2 aminoacids. Alanine is "bigger" than Glycine because it has an additional methyl group. It seems that this difference is enough to keep strobilurins from binding to the cytochrome b Qo site rendering them ineffective. Imagine a small thorn (CH3 group) in a key-hole which hinders the key from entering. One the other hand, this minor change in the Qo cavity does not affect ubiquinone from binding and so the electron transport chain is not negatively affected. For more details see "Re-examination of inhibitor resistance conferred by Qo-site mutations in cytochrome b using yeast as a model system" by Fisher, N., Meunier, B. (2005) Pest Management Science, 61 (10), pp. 973-978.

I hope I helped a little.

Best Regards

Anastasios