Lysine

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General Features
Abbreviation: Lys or K
Molecular Formula: HO₂(CCH(NH₂)(CH₂)₄NH₂

Lysine's codons are AAA and AAG.  It is a base.  The ε-amino group (a primary amine) can participate in hydrogen bonding.  The ε-amino acid can also serve as a general base in catalysis

Physiological Roles
Lysine has been shown to be essential in the chemotactic response of bacteria, including Escherichia coli and Salmonella typhimurium.  In chemotaxis, the activity of CheA, the histidine protein kinase, is controlled by sensory receptor proteins in the cytoplasmic membrane.  CheA phosphorylates CheY, the chemotaxis response regulator.  CheY interacts with the flagellar motor apparatus and the phosphorylation of CheY results in a tumbling response.  Aspartate has been shown to be the site of phosphorylation.  In close proximity to this site is a lysine residue.  This lysine residue is essential in producing the tumbling motion.  Regardless of the level of phosphorylation, removal of the lysine residue inhibits the tumbling motion.  It is believed that the lysine residue is required for an event after the phosphorylation.  An interaction between the ε-amino of lysine and the phosphoryl group at aspartate is required for the conformational change that leads to the activation of CheY.  More information is available in Roles of the Highly Conserved Aspartate and Lysine Residues in the Respone Regulator of Bacterial Chemotaxis by Gudrun S. Lukat et al.


Synthesis
The synthesis of lysine begins by converting oxaloacetate to aspartate.  Aspartate is then converted to L-aspartyl-4-phosphate.  This is done by aspartokinase and ATP is required.  L-aspartyl-4-phosphate is then converted to aspartate semialdehyde by β-Aspartate semialdehyde dehydrogenase. NADPH provides energy in this step.

The synthesis of lysine has been found to vary in different bacterial species.  A generalized pathway is present below.  Dihydrodipicolinate synthase adds pyruvate and two molecules of water are removed.  Cyclization then occurs forming 2,3-dihydrodipicolinate.  The product is then reduced by dihydrodipicolinate reducatase, consuming a NADPH molecule.  Tetrahydrodipicolinate N-acetyltransferase opens the ring.  Two molecules of water and one acyl-CoA (or succinyl-CoA) are used in this step.  The group added from CoA protects the amino group from attack during transamination by glutamate.

Succinyl diaminopimelate aminotransferase catalyzes the formation of N-succinyl-LL-2,6-diaminoheptanedionate.  Glutaric acid is used and an oxoacid is produced in this reaction.  An acyldiaminopimelate deacylase converts the product into LL-2,6-diaminoheptanedionate.  This is then converted into meso-2,6-diamino-heptanedionate by diaminopimelate epimerase.  Finally, diaminopimelate decarboxylase converts meso-2,6-diamino-heptanedionate into L-lysine.

http://en.wikipedia.org/wiki/File:Lysine_Biosynthesis.png

The synthesis of lysine has been found to vary in different bacterial species.  For more information on different synthesis pathways, please read A Functional Split Pathway for Lysine Synthesis in Corynebacterium glutamicum  Barbel Schrumpf et al.