Redesign of carnitine acetyltransferase specifity by protein engineering

dc.contributor
Universitat de Barcelona. Departament de Bioquímica i Biologia Molecular (Farmàcia)
dc.contributor.author
García Cordente, Antonio Felipe
dc.date.accessioned
2011-04-12T13:23:51Z
dc.date.available
2006-08-03
dc.date.issued
2006-06-22
dc.date.submitted
2006-08-03
dc.identifier.isbn
8469003976
dc.identifier.uri
http://www.tdx.cat/TDX-0803106-105451
dc.identifier.uri
http://hdl.handle.net/10803/1047
dc.description.abstract
In eukaryotes, L-carnitine is involved in energy metabolism, where it facilitates b-oxidation of fatty acids. Carnitine acyltransferases catalyze the reversible conversion of acyl-CoA and carnitine to acylcarnitine and free CoA. There are three carnitine acyltransferase families, which differ in their acyl-chain length selectivity: carnitine palmitoyltransferases (CPTs) catalyze long-chain fatty acids, carnitine octanoyltransferase (COT) prefers medium-chain fatty acids, and carnitine acetyltransferase (CrAT) uses short-chain acyl-CoAs. <br/><br/>In this study, we attempted to identify the amino acid residues responsible for acyl-CoA specificity in the acyltransferase family through structure-based mutagenesis studies. We identified an amino acid (Met564 in rat CrAT) that is critical to fatty acyl chain-length specificity. A CrAT protein carrying the M564G mutation behaved as if its natural substrates were medium-chain acyl-CoAs, similar to COT. In the reverse case, mutation of the orthologous glycine (Gly553) to methionine in COT decreased activity towards its natural substrates, medium-chain acyl-CoAs, and increased activity towards short-chain acyl-CoAs. A second putative amino acid involved in acyl-CoA specificity was identified (Asp356 in rat CrAT), and the double CrAT mutant D356A/M564G behaved as a pseudo-CPT in terms of substrate specificity. Three-dimensional models revealed a deeper hydrophobic cavity for the binding of acyl groups in both CrAT mutants in the same position as the shallow cavity in the wt enzyme. Furthermore, we studied the effect of C75-CoA, a potent and competitive inhibitor of CPT I, on CrAT activity. C75-CoA occupies the same pocket in CPT I as palmitoyl-CoA, suggesting an inhibitory mechanism based on mutual exclusion. To determine whether this inhibitor would fit in the open hydrophobic pocket formed in CrAT mutants M564G and D356A/M564G, we carried out competitive inhibition assays. Our experiments showed that while C75-CoA is a potent inhibitor of CrAT mutants M564G and D356A/M564G, it has no effect on wt CrAT. <br/>Choline acetyltransferase (ChAT) catalyzes a similar reaction to CrAT, with the difference that in ChAT the acetyl group from acetyl-CoA is transferred to choline instead of carnitine. Cronin (1998) successfully redesigned ChAT to use carnitine instead of its natural substrate choline. In the present study, our aim was to achieve the opposite, that is, to redesign rat CrAT specificity from carnitine to choline. We prepared a mutant CrAT that incorporates four amino acid substitutions, and the resulting mutant shifted the catalytic discrimination between L-carnitine and choline in favour of the latter substrate. <br/>The food industry is interested in the production of esters for use as flavouring compounds; for example, esters are responsible for the fruity character of fermented alcoholic beverages such as beer and wine. Esters are produced in an enzyme-catalyzed reaction between a higher alcohol and an acyl-CoA molecule. Since CrAT is responsible for the modulation of the acyl-CoA/CoA ratio, we hypothesized that overexpression of this enzyme could modify ester production in yeast. Therefore, we overexpressed CrAT in yeast and analysed its effect on ester production during alcoholic fermentation. Compared with control cells, overexpression of CrAT caused a significant reduction in the production of some esters, including the important flavour components ethyl acetate and 3-methyl-butyl acetate.<br/>In conclusion, the amino acid substitutions in rat CrAT and COT in this study reveal several residues that are involved in substrate recognition and provide insight into the molecular requirements for their correct positioning in order to achieve efficient catalysis. These results not only help us to understand the structure-function relationship within the acyltransferase family, but may also facilitate studies on obesity, non-insulin dependent diabetes, and patients with defective â-oxidation. Moreover, our results open the possibility of biotechnological applications of the enzymes of the carnitine acyltransferase family in the wine industry.
eng
dc.format.mimetype
application/pdf
dc.language.iso
eng
dc.publisher
Universitat de Barcelona
dc.rights.license
ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs.
dc.source
TDX (Tesis Doctorals en Xarxa)
dc.subject
Metabolisme
dc.subject
Enginyeria genètica
dc.subject
Biomedicina
dc.subject.other
Ciències de la Salut
dc.title
Redesign of carnitine acetyltransferase specifity by protein engineering
dc.type
info:eu-repo/semantics/doctoralThesis
dc.type
info:eu-repo/semantics/publishedVersion
dc.subject.udc
577
cat
dc.contributor.director
Serra i Cucurull, Dolors
dc.contributor.director
García Hegardt, Fausto
dc.rights.accessLevel
info:eu-repo/semantics/openAccess
dc.identifier.dl
B. 42279-2006


Documentos

00.AGC_PREVIOUS.pdf

60.12Kb PDF

01.AGC_INTRODUCTION.pdf

690.6Kb PDF

02.AGC_OBJECTIVES.pdf

12.82Kb PDF

03.AGC_MATERIALS_AND_METHODS.pdf

223.3Kb PDF

04.AGC_RESULTS.pdf

746.3Kb PDF

05.AGC_DISCUSSION.pdf

117.3Kb PDF

06.AGC_CONCLUSIONS.pdf

18.41Kb PDF

07.AGC_REFERENCES.pdf

44.45Kb PDF

08.AGC_APPENDIX.pdf

225.4Kb PDF

09.AGC_PUBLICATIONS.pdf

2.958Mb PDF

10.AGC_RESUM_CATALA.pdf

96.89Kb PDF

Este ítem aparece en la(s) siguiente(s) colección(ones)