Atypical Biosynthetic Properties of a Δ 12 /ν+3 Desaturase from the Model Basidiomycete Phanerochaete chrysosporium

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Abstract
The model white-rot basidiomycete Phanerochaete chrysosporium contains a single integral membrane Δ 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 ν+3 regioselectivity, where the site of desaturation is three carbons carboxy-distal to the reference position of a preexisting double bond (ν). 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°C versus 15°C). Thus, while maintaining the hallmark activity of the fatty acyl Δ 12 -desaturase family, the basidiomycete fad2 genes appear to have evolved substantially from an ancestral desaturase.