Comparison of aldehyde-producing activities of cyanobacterial acyl-(acyl carrier protein) reductases.
BACKGROUND
Biosynthesis of alkanes is an attractive way of producing substitutes for petroleum-based alkanes. Acyl-[acyl carrier protein (ACP)] reductase (AAR) is a key enzyme for alkane biosynthesis in cyanobacteria and catalyzes the reduction of fatty acyl-ACP to fatty aldehydes, which are then converted into alkanes/alkenes by aldehyde-deformylating oxygenase (ADO). The amino acid sequences of AARs vary among cyanobacteria. However, their differences in catalytic activity, substrate specificity, and solubility are poorly understood.


RESULTS
We compared the aldehyde-producing activity, substrate specificity, and solubility of AARs from 12 representative cyanobacteria. The activity is the highest for AAR fromSynechococcus elongatusPCC 7942, followed by AAR fromProchlorococcus marinusMIT 9313. On the other hand, protein solubility is high for AARs from PCC 7942,Microcystis aeruginosa,Thermosynechococcus elongatusBP-1,Synechococcussp. RS9917, andSynechococcussp. CB0205. As a consequence, the amount of alkanes/alkenes produced inEscherichia colicoexpressing AAR and ADO is the highest for AAR from PCC 7942, followed by AARs from BP-1 and MIT 9313. Strikingly, AARs from marine and freshwater cyanobacteria tend to have higher specificity toward the substrates with 16 and 18 carbons in the fatty acyl chain, respectively, suggesting that the substrate specificity of AARs correlates with the type of habitat of host cyanobacteria. Furthermore, mutational analysis identified several residues responsible for the high activity of AAR.


CONCLUSIONS
We found that the activity, substrate specificity, and solubility are diverse among various AARs. Our results provide a basis for selecting an AAR sequence suitable for metabolic engineering of bioalkane production while regulating carbon chain length.
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan.
Hisashi
H
Kudo
Department of Pure and Applied Sciences, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan.
Ryota
R
Nawa
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan ; Department of Pure and Applied Sciences, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan.
Yuuki
Y
Hayashi
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan ; Department of Pure and Applied Sciences, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902 Japan ; Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 Japan.
Munehito
0000-0002-1223-2242
M
Arai
Acyl-ACP reductase; Aldehyde-deformylating oxygenase; Bioalkane; Cyanobacteria; Fatty aldehyde