Salt induction of fatty acid elongase and membrane lipid modifications in the extreme halotolerant alga Dunaliella salina.
In studies of the outstanding salt tolerance of the unicellular green alga Dunaliella salina, we isolated a cDNA for a salt-inducible mRNA encoding a protein homologous to plant beta-ketoacyl-coenzyme A (CoA) synthases (Kcs). These microsomal enzymes catalyze the condensation of malonyl-CoA with acyl-CoA, the first and rate-limiting step in fatty acid elongation. Kcs activity, localized to a D. salina microsomal fraction, increased in cells transferred from 0.5 to 3.5 M NaCl, as did the level of the kcs mRNA. The function of the kcs gene product was directly demonstrated by the condensing activity exhibited by Escherichia coli cells expressing the kcs cDNA. The effect of salinity on kcs expression in D. salina suggested the possibility that salt adaptation entailed modifications in the fatty acid composition of algal membranes. Lipid analyses indicated that microsomes, but not plasma membranes or thylakoids, from cells grown in 3.5 M NaCl contained a considerably higher ratio of C18 (mostly unsaturated) to C16 (mostly saturated) fatty acids compared with cells grown in 0.5 M salt. Thus, the salt-inducible Kcs, jointly with fatty acid desaturases, may play a role in adapting intracellular membrane compartments to function in the high internal glycerol concentrations balancing the external osmotic pressure.
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel.
Malkit
M
Azachi
Avi
A
Sadka
Morly
M
Fisher
Paulina
P
Goldshlag
Irena
I
Gokhman
Ada
A
Zamir
D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D000123:Acetyltransferases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000460:Chlorophyta / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D044943:Fatty Acid Desaturases / Q000378:metabolism; D000081031:Fatty Acid Elongases; D005227:Fatty Acids / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D008563:Membrane Lipids / Q000378:metabolism*; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology*
D018076:DNA, Complementary; D005227:Fatty Acids; D008563:Membrane Lipids; D012333:RNA, Messenger; D012965:Sodium Chloride; D044943:Fatty Acid Desaturases; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase