1: Plant Mol Biol 1994 Feb;24(4):643-50
Identification of conserved domains in the delta 12 desaturases of
cyanobacteria.

Sakamoto T, Wada H, Nishida I, Ohmori M, Murata N
Department of Molecular Biomechanics, Graduate University of Advanced Studies,
Okazaki, Japan.

Cyanobacterial genes for enzymes that desaturate fatty acids at the delta 12
position, designated desA, were isolated from Synechocystis PCC6714,
Synechococcus PCC7002 and Anabaena variabilis by cross-hybridization with a DNA
probe derived from the desA gene of Synechocystis PCC6803. The genes of
Synechocystis PCC6714, Synechococcus PCC7002 and A. variabilis encode proteins
of 349, 347 and 350 amino acid residues, respectively. The transformation of
Synechococcus PCC7942 with the desA genes from Synechocystis PCC6714,
Synechococcus PCC7002 and A. variabilis was associated with the ability to
introduce a second double bond at the delta 12 position of fatty acids. The
amino acid sequence of the products of the desA genes revealed the presence of
four conserved domains. Since one of the conserved domains was also found in the
amino acid sequences of omega 3 desaturases of Brassica napus and mung bean,
this domain may play an essential role in the introduction of a double bond into
fatty acids bound to membrane lipids.
PMID: 8155883


2: Plant Mol Biol 1994 Oct;26(1):249-63
Cloning of omega 3 desaturase from cyanobacteria and its use in altering the
degree of membrane-lipid unsaturation.

Sakamoto T, Los DA, Higashi S, Wada H, Nishida I, Ohmori M, Murata N
Department of Molecular Biomechanics, Graduate University of Advanced Studies,
Okazaki, Japan.

Cyanobacteria respond to a decrease in temperature by desaturating fatty acids
of membrane lipids to compensate for the decrease in membrane fluidity. Among
various desaturation reactions in cyanobacteria, the desaturation of the omega 3
position of fatty acids is the most sensitive to the change in temperature. In
the present study, we isolated a gene, designated desB, for the omega 3
desaturase from the cyanobacterium, Synechocystis sp. PCC 6803. The desB gene
encodes a protein a 359 amino-acid residues with molecular mass of 41.9 kDa. The
desB gene is transcribed as a monocistronic operon that produced a single
transcript of 1.4 kb. The level of the desB transcript in cells grown at 22
degrees C was 10 times higher than that in cells grown at 34 degrees C. In order
to manipulate the fatty-acid unsaturation of membrane lipids, the desB gene in
Synechocystis sp. PCC 6803 was mutated by insertion of a kanamycin-resistance
gene cartridge. The resultant mutant was unable to desaturate fatty acids at the
omega 3 position. The desA gene, which encodes the delta 12 desaturase of
Synechocystis sp. PCC 6803, and the desB gene were introduced into Synechococcus
sp. PCC 7942. Whilst the parent cyanobacterium can only desaturate membrane
lipids at the delta 9 position of fatty acids, the resultant transformant was
able to desaturate fatty acids of membrane lipids at the delta 9, delta 12 and
omega 3 positions. These results confirm the function of the desB gene and
demonstrate that it is possible to genetically manipulate the fatty-acid
unsaturation of membrane lipids in cyanobacteria.
PMID: 7524725


3: J Biol Chem 1994 Oct 14;269(41):25576-80
delta 9 Acyl-lipid desaturases of cyanobacteria. Molecular cloning and substrate
specificities in terms of fatty acids, sn-positions, and polar head groups.

Sakamoto T, Wada H, Nishida I, Ohmori M, Murata N
National Institute for Basic Biology, Okazaki, Japan.

In cyanobacteria, the biosynthesis of unsaturated fatty acids is initiated by
delta 9 acyl-lipid desaturase which introduces the first double bond at the
delta 9 position of a saturated fatty acid that has been esterified to a
glycerolipid. We have cloned genes, designated desC, for delta 9 acyl-lipid
desaturases from two cyanobacteria, namely Anabaena variabilis and Synechocystis
sp. PCC 6803. These desaturases, when expressed in Escherichia coli, desaturated
stearic acid to yield oleic acid at the C-1 positions of
phosphatidylethanolamine and phosphatidylglycerol, but did not desaturate
palmitic acid, palmitoleic acid, and cis-vaccenic acid. These results indicate
that the delta 9 acyl-lipid desaturases are specific to stearic acid esterified
at the C-1 position of a glycerolipid and are nonspecific with respect to the
polar head group of the glycerolipid. The deduced amino acid sequences of the
delta 9 acyl-lipid desaturases are similar in part to those of stearoyl-CoA
desaturases of the rat, the mouse, and Saccharomyces cerevisiae, but not to
those of acyl-(acyl-carrier-protein) desaturases of higher plants.
PMID: 7929259