Crystal structure of ADL1, a plant-specific homologue of the universal diaminopimelate amino transferase enzyme of lysine biosynthesis
Vladimir Sobolev, Marvin Edelman, Orly Dym, Tamar Unger, Shira Albeck, and Gad Galili[1]
Molecular Tour
The Arabidopsis “Aberrant growth and death-2” (AGD2) protein was originally identified as a protein that is associated with pathogen resistance. The AGD2 protein was subsequently identified as the diaminopimelate amino transferase (DAPAT) enzyme. An Arabidopsis homologue of this protein was subsequently identified and originally named as the AGD2-like defense response protein 1 (ALD1). Both DAPAT and ALD1 require pyridoxal-5′-phosphate (PLP) for their activities. Here we report the structure of the ALD1 protein from Arabidopsis thaliana (AtALD1), to a resolution of 2.1 Å.
(PDB entry 2z20), with an RMSD between structures of 0.64 Å over 324 Cα atoms. AtALD1 is in cyan and AtDAPAT is in yellow. The largest difference between the two structures can be seen at the carboxy terminal regions of two helices: helix α2 (residues 37-53) and helix α12 (residues 373-386). There is a difference of about 6 Å at the loop edge carboxy-terminal to helix α2, between the Cα atom of Asn49 in AtALD1 and the structurally aligned Cα atom of Asp55 in AtDAPAT. Helix α2 diverges between the two structures mainly because of differences in the dihedral angles of Gly36 and Tyr37 in AtALD1 loop 33-37 verses its AtDAPAT counterparts. On the other hand, differences in helix α12 occur because of non-dramatic changes in dihedral angles of all the residues of loop 370-373.
(RMSD following superimposition equals 0.48 Å over 13 Cα atoms). Carbon atoms of PLP complexed with AtALD1 are in green, carbon atoms of PLP complexed with AtDAPAT are in darkmagenta, nitrogen, oxygen, and phosphorus atoms are colored in blue, red, and orange, respectively. Lys129 and Tyr152 of AtDAPAT are labeled in yellow and Gln123 and Phe146 in AtALD1 are labeled in cyan. While , it is likely that side chain replacement upon mutation to Gln does not significantly change the position of these atoms and their contacts. Furthermore, PLP has only minor contact (about 1 Å2) with the side chain oxygen of Tyr152. Therefore, replacement Tyr by Phe at these positions should not affect PLP binding.
