A novel sterol desaturase like gene promoting dealkylation of phytosterols in Tetrahymena thermophila

MARIELA L. TOMAZIC; SEBASTIÁN R. NAJLE; ALEJANDRO D. NUSBLAT; ANTONIO D. UTTARO; CLARA B. NUDEL

EUKARYOTIC CELL

AMER SOC MICROBIOLOGY

Lugar: Washington, DC; Año: 2011 vol. 10 p. 423 - 434

1535-9778

The gen 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 separated cluster, more related to bacterial than to eukaryotic proteins, suggesting a possible horizontal gene transfer event. The somatic knock out of DES24 revealed that encodes a protein, Des24p, which is involved in dealkylation of phytosterols. Knocked out mutants were unable to eliminate the C-24 ethyl group from C29 sterols, whereas the ability to introduce other modifications such as desaturations in position C-5(6), C-7(8) and C-22(23) where not altered. Although C-24 dealkylations have been described in other organisms, such as insects, neither the enzymes nor the corresponding genes were identified up 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 C29 sterols; in this culture condition, a change from the typical pear-like shape to a round shape, plus 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 different mechanism than the currently known.