Abstract
The model white-rot basidiomycete Phanerochaete chrysosporium contains a single integral membrane Delta(12)-desaturase FAD2 related to the endoplasmic reticular plant FAD2 enzymes. The fungal fad2-like gene was cloned and distinguished itself from plant homologs by the presence of four introns and a significantly larger coding region. The coding sequence exhibits ca. 35% sequence identity to plant homologs, with the highest sequence conservation found in the putative catalytic and major structural domains. In vivo activity of the heterologously expressed enzyme favors C(18) substrates with nu+3 regioselectivity, where the site of desaturation is three carbons carboxy-distal to the reference position of a preexisting double bond (nu). Linoleate accumulated to levels in excess of 12% of the total fatty acids upon heterologous expression of P. chrysosporium FAD2 in Saccharomyces cerevisiae. In contrast to the behavior of the plant FAD2 enzymes, this oleate desaturase does not 12-hydroxylate lipids and is the first example whose activity increases at higher temperatures (30 degrees C versus 15 degrees C). Thus, while maintaining the hallmark activity of the fatty acyl Delta(12)-desaturase family, the basidiomycete fad2 genes appear to have evolved substantially from an ancestral desaturase.