Alanine lipids

LIPOAMINO ACIDS :

N-ACYL and ESTER DERIVATIVES of AMINO ACIDS

Several types of derivatives are known according to their amino acid moiety:

1 – Lysine-containing lipids

Some of them are known as Siolipin A. In these compounds lysine is N-linked to a fatty acid (normal or hydroxylated, R₁) and to a fatty alcohol (R₂) (ester link). They are found in Streptomyces species of bacteria.

2 – Ornithine-containing lipids

In these lipids ornithine is linked to a fatty acid (R1) by an amide link and to a long-chain fatty alcohol (R2) by an ester link.

The fatty acid chain (R1) has 16 to 18 carbon atoms and the fatty alcohol may have a cyclopropane ring. They occur in photosynthetic purple bacteria (Gorshein A, Biochim Biophys Acta 1968, 152, 358).
Less complex forms containing ornithine linked to fatty acids only were also described.

Other ornithine-containing lipids are found in Gram negative bacteria and have been reported in some Gram-positives, like Mycobacterium and Streptomyces species but are absent in Archaea and Eukarya (Geiger O et al., Prog Lipid Res 2010, 49, 46). They are commonly formed of a 3-hydroxy fatty acyl group that is attached in amide linkage to the a-amino group of ornithine an a second fatty acyl group is ester-linked to the 3-hydroxy position of the first fatty acid.

a-N-(Acyloxyacyl)-ornithine

3- Glycine-containing lipids

The glycine-containing lipids have been identified in the gliding bacterium Cytophaga johnsonae (Kawazoe R et al., J Bacteriol 199, 173, 5470) and the Gram-negative sea-water bacterium Cyclobacterium marinus (Batrakov SG et al., Chem Phys Lipids 1999, 99, 139). These lipids consist of the amino acid glycine and two fatty acyl residues, using the acyl-oxyacyl structure. The structure of glycine lipid from C. marinus is mainly a N-[3-D-(13-methyltetradecanoyloxy)- 15-methylhexadecanoyl]glycine (see figure below). In this structure, an iso-3-hydroxyfatty acyl group is amide-linked to glycine and its 3-hydroxy group is esterified to another iso-fatty acid.

Glycine-containing lipid