In vivo overproduction of the pentafunctional arom polypeptide in Aspergillus nidulans affects metabolic flux in the quinate pathway.
The shikimate pathway and the quinic acid utilisation (QUT) pathway of Aspergillus nidulans and other fungi share the two common metabolic intermediates, 3-dehydroquinic acid (DHQ) and dehydroshikimic acid (DHS), which are interconverted by two isoenzymes, catabolic 3-dehydroquinase, (cDHQase) and biosynthetic dehydroquinase, (bDHQase). bDHQase is one of five consecutive enzymatic activities associated with the pentafunctional arom protein encoded by the complex AROM locus, whereas cDHQase is encoded by the single-function QUTE gene, one of seven genes comprising the QUT gene cluster in A. nidulans, which is required for the catabolism of quinate to protocatechuate. We addressed the question of how much (if any) leakage there is of the two common substrates between the two pathways, by increasing the concentration of the arom protein in vivo by means of recombinant DNA technology. We demonstrated that constitutive overproduction of the arom protein by 12-fold in the presence of quinate inhibits germination of conidiospores, but showed that 12-fold quinate-inducible overproduction of arom protein does not have this effect. In addition we showed that a qutE mutant (lacking cDHQase) can grow with quinic acid as sole carbon source whtn the arom protein is overproduced fivefold. The data are most simply interpreted as simple competition for common substrates by the enzymes of the two pathways and demonstrate that any channelling function of the arom protein in vivo is relatively leaky.
Lamb
H K
HK
Department of Biochemistry and Genetics, Medical School, University of Newcastle upon Tyne, UK.
Bagshaw
C R
CR
Hawkins
A R
AR
D000429:Alcohol Oxidoreductases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001233:Aspergillus nidulans / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D015139:Blotting, Southern; D002474:Cell-Free System / Q000378:metabolism; D006836:Hydro-Lyases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008190:Lyases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D009097:Multienzyme Complexes / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010770:Phosphotransferases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D011401:Promoter Regions, Genetic / Q000235:genetics; D011801:Quinic Acid / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012765:Shikimic Acid / Q000378:metabolism*; D013172:Spores, Fungal / Q000502:physiology; D014166:Transferases; D014170:Transformation, Genetic
D007527:Isoenzymes; D009097:Multienzyme Complexes; D011993:Recombinant Fusion Proteins; C019728:arom enzyme; D011801:Quinic Acid; D012765:Shikimic Acid; D000429:Alcohol Oxidoreductases; D014166:Transferases; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D008190:Lyases; D006836:Hydro-Lyases