Structural determinants for cold regulation in methyl-end desaturases of trypanosomatids.

ALLOATTI, ANDRÉS; UTTARO, ANTONIO

Mar del Plata, Buenos Aires, Argentina

Congreso; SAIB 43rd Annual Meeting; 2007

Sociedad Argentina de Investigaciones Bioquímicas y Biología Molecular

We have previously characterized trypanosomatid desaturases involved in the conversion of oleoyl- to linoleoyl-moieties of phospholipids in the endoplasmic reticulum membrane of the parasites. Trypanosoma brucei and Leishmania major oleoyl desaturases share 56% of identity and 75% of similarity, and comparable percentage of conversion (in vivo) of 16:1 and 18:1 fatty acids into 16:2 and 18:2 respectively, when expressed in yeasts at 30 ºC. Interestingly, T. brucei desaturase showed an increased substrate conversion at lower temperatures, more significant for 16:1, whereas L. major enzyme has the opposite effect.Analysis of primary structure for both enzymes revealed a conserved theoretical membrane topology and consensus sequences for the three clusters of histidines, presumed to be part of the active site. However, both desaturases show some significant differences in certain regions, for example in the N-terminus or the catalytic domain located between the first and second hydrophobic domains. Construction of truncated and chimeric desaturases between the orthologous genes allowed us to localize a region involved in thermal regulation near the second histidine cluster. This region is a 20 aminoacid domain that has differences in charge and in the volume of some aminoacidic residues. We propose that this domain is also involved in the substrate selectivity of the desaturases.