A novel sterol desaturase-like protein promoting dealkylation of phytosterols in Tetrahymena thermophila.
The gene TTHERM_00438800 (DES24) from the ciliate Tetrahymena thermophila encodes a protein with three conserved histidine clusters, typical of the fatty acid hydroxylase superfamily. Despite its high similarity to sterol desaturase-like enzymes, the phylogenetic analysis groups Des24p in a separate cluster more related to bacterial than to eukaryotic proteins, suggesting a possible horizontal gene transfer event. A somatic knockout of DES24 revealed that the gene encodes a protein, Des24p, which is involved in the dealkylation of phytosterols. Knocked-out mutants were unable to eliminate the C-24 ethyl group from C(29) sterols, whereas the ability to introduce other modifications, such as desaturations at positions C-5(6), C-7(8), and C-22(23), were not altered. Although C-24 dealkylations have been described in other organisms, such as insects, neither the enzymes nor the corresponding genes have been identified to date. Therefore, this is the first identification of a gene involved in sterol dealkylation. Moreover, the knockout mutant and wild-type strain differed significantly in growth and morphology only when cultivated with C(29) sterols; under this culture condition, a change from the typical pear-like shape to a round shape and an alteration in the regulation of tetrahymanol biosynthesis were observed. Sterol analysis upon culture with various substrates and inhibitors indicate that the removal of the C-24 ethyl group in Tetrahymena may proceed by a mechanism different from the one currently known.
Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
Mariela L
ML
Tomazic
Sebastián R
SR
Najle
Alejandro D
AD
Nusblat
Antonio D
AD
Uttaro
Clara B
CB
Nudel
D000595:Amino Acid Sequence; D003640:Dealkylation; D044943:Fatty Acid Desaturases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010840:Phytosterols / Q000378:metabolism*; D016415:Sequence Alignment; D013261:Sterols / Q000378:metabolism*; D016808:Tetrahymena thermophila / Q000737:chemistry / Q000145:classification / Q000201:enzymology* / Q000235:genetics
D010840:Phytosterols; D013261:Sterols; D044943:Fatty Acid Desaturases
Semin Cell Dev Biol. 2005 Apr;16(2):175-82
15797828
Trends Genet. 2002 Jan;18(1):35-40
11750699
Biochim Biophys Acta. 1982 Dec 22;693(2):335-40
6818990
J Biol Chem. 1970 Mar 25;245(6):1247-54
5442819
Proc Natl Acad Sci U S A. 2002 Mar 19;99(6):3734-9
11891286
Biochemistry. 2000 Feb 1;39(4):701-11
10651635
Lipids. 1985 Mar;20(3):158-66
3990524
J Eukaryot Microbiol. 2005 Jan-Feb;52(1):61-7
15702982
Parasitol Res. 2006 Feb;98(3):194-9
16323024
Mol Biol Evol. 2007 Aug;24(8):1596-9
17488738
Annu Rev Cell Dev Biol. 2006;22:129-57
16753029
Lipids. 1987 Jun;22(6):386-96
27519734
Nucleic Acids Res. 2007 Jan;35(Database issue):D237-40
17135202
Arabidopsis Book. 2002;1:e0004
22303189
Nucleic Acids Res. 1994 Dec 11;22(24):5391-8
7816630
J Nematol. 1986 Jan;18(1):9-17
19294131
J Mol Evol. 2004 May;58(5):540-9
15170257
Plant Physiol. 2007 Jan;143(1):461-72
17114270
Cell Mol Life Sci. 2005 Jun;62(11):1182-97
15761667
Genetics. 1997 May;146(1):135-47
9136007
J Biol Chem. 1969 May 10;244(9):2325-33
5783836
Genome Biol Evol. 2009 Sep 10;1:364-81
20333205
J Gen Microbiol. 1988 Jun;134(6):1441-7
3221193
Biochemistry. 1994 Nov 1;33(43):12787-94
7947684
Lipids. 1975 Mar;10(3):140-4
805331
Cell Biol Int. 1998 Nov;22(11-12):875-8
10873299
Annu Rev Entomol. 2002;47:883-916
11729094
J Protozool. 1968 Aug;15(3):600-5
5703082
Cell Biochem Funct. 2003 Mar;21(1):19-26
12579517
Lipids. 1978 Oct;13(10):692-6
102891
Eukaryot Cell. 2009 Aug;8(8):1287-97
19525418
PLoS One. 2008 Aug 06;3(8):e2883
18682733
J Lipid Res. 1981 Jul;22(5):770-7
6793681
Nucleic Acids Res. 1994 Nov 11;22(22):4673-80
7984417
PLoS Biol. 2006 Sep;4(9):e286
16933976