“Piano principle” helped to understand how fungi synthetize compounds valuable for biotechnology

Newswise — Unexpected model was suggested by the scientist of The Federal Research Centre “Fundamentals of Biotechnology” of the Russian Academy of Sciences (Research Center of Biotechnology RAS). The author of the scientific review compared extracting of sounds by musical instrument with the process of synthesis of biologically active compounds by fungi. The model of regulation of secondary metabolism according to the piano principle simply and clearly explains a mechanism of activation of biosynthetic gene clusters (BGCs), that lead to biosynthesis of corresponding secondary metabolites, and also points to ways of increasing productivity of high-yielding strains. Results of the research were published in International Journal of Molecular Sciences.

Filamentous fungi, the main morphological form of which, the mycelium, resembles an accumulation of thin intertwined strands, are widely used in biotechnology for the production of drugs such as antibiotics, statins, and immunosuppressants. Certain species of these fungi are capable of synthesizing more than a hundred biologically active compounds called secondary metabolites.

However, in the concrete period of life only some of these substances are synthetized. It depends not only on a stage of development of microorganism but also on the environment. Synthesis of different secondary metabolites is controlled by “switch-on” and “switch-off” of a corresponding biosynthetic genes, assembled in so-called biosynthetic gene clusters (BGC) as a reaction on inner and outer signals.

As we know the principles of activation and suppression of these genes, scientists make attempts to manage the ability of fungi to synthetize compounds, important for biotechnology and medicine, thus improving producer strains. In the last decades researchers from all over the world have accumulated an enormous volume of information about synthesis of secondary metabolites in fungi. In this connection there is a necessity in summarizing all data and creating a model that is able to describe it simply and clearly.

Alexander Zhgun, Candidate of Sciences in Biology, head of the group of genetic engineering of fungi of  The Federal Research Centre “Fundamentals of Biotechnology” of the Russian Academy of Sciences on the base of classification of fungal secondary metabolites, their gene clusters and hierarchical system of regulation offered a model, that summarizes a lot of complex processes, that take place in cells of Filamentous fungi during the synthesis of secondary metabolites. As a synthesis of every of these compounds “is started” as an answer for a certain signal, the scientist compared it with piano principle, that makes a definite sound as an answer for pressing of this or that key.

“Inside each cell of a fungi there is a kind of musical instrument, a specific piano, that enables by pressure on a definite key – activation of gene cluster – to make a certain sound – produce targeted secondary metabolite”, – tells Alexander Zhgun.

Thus, according to suggested model, when there are no signals from the environment, genes, that answer for the synthesis of secondary metabolites, are inactive and in position of so-called heterochromatin – tightly packed parts of DNA. RNA polymerase, responsible for reading information from genes (for subsequent synthesis of enzymes for biosynthetic pathway), cannot approach to such parts, and it can be compared with the case when piano lid is closed and music stand is lowered. As a musician cannot make sounds from a closed instrument, fungi’s cell won’t be able to synthetize secondary metabolites.

To start synthesis, genes are taken to the state available for regulatory proteins and proteins of tool of transcription. In this case, the part of DNA containing the BGC corresponding to the signal ceases to be tightly packed and becomes euchromatin. In the similar way when piano is prepared to work, a musician can press keys and that brings to sound production. By this in the presented model each key corresponds to a separate BGC, the activation of which leads to the synthesis of a specific low-molecular weight compound.

Interestingly that the author of the scientific review with the help of his model also explains the fact that outer signals, on which Filamentous fungi react, can differ in intensity.

“As a musician can get different sounds as far as length, loudness and character of sound’s attenuation by pressing one and the same piano key differently, so microorganisms can regulate the amount of synthesized by them compound. Naturally, in living cells this dependence is more complex and not always lineal, that is explained by complex and hierarchical system of regulation, coordinating reactions of metabolism”, – explains the author of the article. 

In order to make this model clearer and more precise the scientist the scientist proposed comparing the regulation of the synthesis of secondary metabolites with a more complex musical instrument - an organ with several rows of keys or keyboards.

Such analogy seemed more concrete to the scientist, because Filamentous fungi usually have not one chromosome (as one row of keys on the piano), but several (from two to several tens). Accordingly, the activation of genes responsible for the synthesis of secondary metabolites and located on different chromosomes can be compared to pressing keys on different keyboards of an organ.

“To illustrate how this model works using an organ example, I examined information about the location of BGSc in the model organism Penicillium chrysogenum. This organism is used in biotechnology to produce one of the most important antibiotics for humans, penicillin G, the use of which made a coup in medicine in the early 1940s. P. сhrysogenum has 4 chromosomes, therefore, its “organ” contains 4 keyboards. I mapped the currently known gene clusters to show the mosaic nature of their location. Nature must be a virtuoso pianist to consistently play such distant keys in response to incoming signals”, -tells Alexander Alexandrovich.

The piano model also enables to explain how you can “make” fungi to produce a needed compound in enormous amount. Normally microorganisms have special “molecular limiters” that don’t enable them to produce abundant amount of a product. The same way a good piano has restrictions as far as strength and length of a sound, that is made by pressing on this or that key, is concerned. However, if you damage an instrument, you can make the only one needed key left and it will make a sound constantly and very loudly.

“In the case of Filamentous fungi such distortions can be made with the help of change in system of regulation of secondary metabolism and biosynthetic clusters, responsible for the production of alternative (extrinsic) metabolites. In biotechnology such distortions were found in high-yielding strains, obtained during the last 70-80 years as a result of random mutagenesis and selection. They enable to get antibiotics and other secondary metabolites, used in medicine and industry, in large quantities”, – tells Alexander Zhgun.

“The suggested by the scientist model offers a fresh look on principles of regulation of secondary metabolite among Filamentous fungi. It enables to understand better, how a human can artificially govern the activity of genes and productivity of microorganisms. Thanks to that fact therein expressed principles are of practical interest to biotechnology.