Sandbox GGC4

<Structure load='1x2h' size='350' frame='true' align='right' caption='Insert caption here' scene='Insert optional scene name here' />==''e.Coli'' Lipoate Protein Ligase A complex with Lipoic Acid==

<scene name='75/752268/Lipate__protein_ligase__main/1'>Crystallized Lipoate Protein Ligase A</scene><ref>PMID:16043486</ref>

 

Lipoic Acid Is a prosthetic group for many dehydrogenase in ''E. coli'', and it is also needed for enzymes involved in the glycine cleavage system. <ref>PMID:7639702</ref> <ref>PMID:16043486</ref> A key example of the use of lipoic acid as a prosthetic group is the E2 subunit of the pyruvate dehydrogenase complex. <ref>PMID:16043486</ref> Lipoate attaches to a lysine on this subunit, and the sulfur on the ring of lipoic acid binds covalently with the incoming pyruvate to "shuttle" it to the SCoA complex for later use in the citric acid cycle. Lipoate protein Ligase A is the enzyme in ''e.Coli'' that attaches lipoate to the enzymes that need it. <ref>PMID:7639702</ref> Humans Have a homolog to this enzyme, called lipoyltransferase, and the two enzymes share between 31%-35% identity with each other. <ref>PMID:16043486</ref> In contrast to the lipoate protein Ligase A, however, lipoyltransferase in humans is unable to catalyze the first part of the reaction in which an AMP is added to a lipoic acid. <ref>PMID:16043486</ref>

Research has found that lipoate protein Ligase A proteins are present in fairly small numbers in an ''e.coli'' cell (less than 10 per cell). <ref>PMID:7639702</ref> Studies conducted on purified Lipoate protein Ligase found that the enzyme additionally requires Magnesium ions to functions properly, as well as lipoic acid and ATP. <ref>PMID:7639702</ref> Lipoate protein Ligase can use both the R and S enantiomers of Lipoate as substrates, though it has a higher affinity for (R)-Lipoate. <ref>PMID:7639702</ref> <ref>PMID:16043486</ref> in addition to the enantiomers, other molecules similar in structure to lipoate, such as ocatnoate, can be incoporated into the enzymes active site, although with less affinity. <ref>PMID:7639702</ref>

 

Researchers in Japan Successfully isolated lipoate Protein Ligase A from ''e.Coli'' and crystallized it in order to determine the structure. The team divided the protein into two main sections; a Larger <scene name='75/752268/Lpl_a_n_terminus/1'>N terminus unit</scene> section consisting of Amino Acids 1-244, and a smaller, <scene name='75/752268/Lpl_c_terminus/1'>C terminal Unit</scene> consisting of amino acids 253-337. <ref>PMID:16043486</ref> There is a small segment of linker amino acids (245-252) that connect the two subunits. <ref>PMID:16043486</ref> Researchers found that there is a space exposed to solution formed between these two subunits, and this exposed portion is the active site to which lipoic acid binds.<ref>PMID:16043486</ref> <scene name='75/752268/Lipoic_acid_binding_site/1'> Binding Site of Lipoic Acid </scene> The sulfur and carbon ring of lipoic acid is held into place via hydrophobic interactions with Particular Leucine, Phenylalanine, and Alanine residues inside of the active site, as well as some non ring portions of a serine side chain. <ref>PMID:16043486</ref> The carboxylic acid on lipoate was determinedc to held in place by Hydrogen bonding formed with side chains of either Serine-72 or Arginine-140 (researchers saw both results in crystallized protein). <scene name='75/752268/Lpla_active_site/1'>Amino Acids Responsible for holding Lipoate into place</scene> <ref>PMID:16043486</ref> Researchers hypothesized that other compounds similar to lipoate could bind to the active site because of the relatively weak forces that bind the substrate.<ref>PMID:16043486</ref> In the crystallization experiment performed, the team was unable to determine the binding site of ATP on the enzyme, But their Data suggested that the serine-72 implicated in holding the carboxyl group of lipoate also plays an important role in catalyzing the reaction between ATP and lipoate. <ref>PMID:16043486</ref> The researchers also state that this enzyme, as well as some homologs closely related to it, exhibit a <scene name='75/752268/Atp_binding_loop/1'>potential ATP binding pocket</scene> from Amino Acids 69-75. <ref>PMID:16043486</ref> The researchers believe this portion can make both a positive charge (Because of multiple Arginine Residues on this portion and a space that might sterically allow the binding of ATP to the enzyme. <ref>PMID:16043486</ref>