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3. (a) Most antibiotics, or their precursors, are obtained from microorganisms that have been bred to...

Question:

3. (a) Most antibiotics, or their precursors, are obtained from microorganisms that have been bred to produce them in the bes(b) One method of obtaining novel variants of erythromycin is to introduce mutations into the PKS genes and thereby remove th

3. (a) Most antibiotics, or their precursors, are obtained from microorganisms that have been bred to produce them in the best yields from simple nutrient precursors. Recently the field has been changed by successful efforts to clone the genes encoding the enzymes that mediate antibiotic biosynthesis. ( - HO =o HO HO For example, erythronolide 7, which is the precursor of erythromycin, is made by three proteins (DEBS1, DEBS2 and DEBS3), each of which is composed of several domains capable of catalysing a single step in the biosynthetic pathway. DH ER DEBS 1 DEBS 2 DEBS 3 Briefly explain the molecular features that allow the three proteins DEBS1, DEBS2 and DEBS3 to assemble in the correct order, and suggest a reason for why only DEBS1 has an N-terminal AT domain rather than a KS domain. (3 points)
(b) One method of obtaining novel variants of erythromycin is to introduce mutations into the PKS genes and thereby remove the enzyme activity associated with a given domain. By writing down the transformations catalysed by each domain of DEBS1 and DEBS2, select which of the following four novel erythromycin derivatives (8-11) would be obtained if the first enoylreductase domain (ER) in DEBS2 were rendered inactive by mutation. Curly-arrow mechanisms for each step are not required. (4 points) - HO HOU 3 НО HÓFOR НО HO L HO SU HOT НО HÓ HOS HO 8 9 10 11 (c) Briefly explain how erythromycin-producing bacteria (Streptomyces) avoid being killed by the antibiotic, and hence outline a potential problem associated with efforts to obtain novel erythromycin analogues by re-engineering the native gene cluster for erythromycin biosynthesis. (3 points)

Answers

Erythromycin, drug synthesized by the soil bacterium Streptomyces erythraeus and used in the treatment of throat infections, pneumonia, and other diseases. Erythromycin, an antibiotic that inhibits the synthesis of vital proteins in susceptible bacteria, may be either bacteriostatic (i.e., inhibiting bacterial reproduction but not killing bacterial cells) or bactericidal (i.e., killing bacteria by direct action), depending on its concentration and the type of microorganism against which it is used. Among the disease-causing agents susceptible to erythromycin are Staphylococcus aureus, several species of Streptococcus, Mycoplasma species, Legionella pneumophila (the bacterium that causes Legionnaire disease), and Corynebacterium diphtheriae (the causative agent of diphtheria) .

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