The Crystal Structure of the Ivy Δ4-16:0-ACP Desaturase Reveals Structural Details of the Oxidized Active Site and Potential Determinants of Regioselectivity
作者： Jodie E. Guy , Edward Whittle , Desigan Kumaran , Ylva Lindqvist , John Shanklin
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摘要: The multifunctional acyl-acyl carrier protein (ACP) desaturase from Hedera helix (English ivy) catalyzes the Δ4 desaturation of 16:0-ACP and Δ9 18:0-ACP further desaturates Δ9-16:1 or Δ9-18:1 to corresponding Δ4,9 dienes. crystal structure enzyme has been solved 1.95A resolution, both iron-iron distance ∼3.2A presence a μ-oxo bridge reveal this be only reported in oxidized FeIII-FeIII form. Significant differences are seen between active site reduced Ricinus communis (castor) desaturase; His227 coordination Fe2 is lost, side chain Glu224, which bridges two iron ions structure, does not interact with either iron. Although carboxylate shifts have observed on oxidation other diiron proteins, first example residue moving beyond range ions. Comparison ivy castor structures surface amino acids close annulus substrate-binding cavity others lining lower portion that potential determinants their distinct substrate specificities. We propose hypothesis packing explains apparent paradox several residues bulkier than equivalents despite necessity for accommodate three more carbons site.
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