5YII

N-terminal residues are crucial for quaternary structure and active site conformation for the phosphoserine aminotransferase from enteric human parasite E. histolytica.

(2019) Int J Biol Macromol 132: 1012-1023

• PubMed: 30959130 Search on PubMed
• DOI: https://doi.org/10.1016/j.ijbiomac.2019.04.027
• Primary Citation of Related Structures:  
  5YB0, 5YD2, 5YII


• PubMed Abstract: 
  

  Phosphoserine aminotransferase (PSAT) is a pyridoxal-5'phosphate (PLP)-dependent enzyme that catalyzes the second reversible step in the phosphoserine biosynthetic pathway producing serine. The crystal structure of E. histolytica PSAT (EhPSAT) complexed with PLP was elucidated at 3.0 Å resolution and the structures of its mutants, EhPSAT_Δ45 and EhPSAT_Δ4, at 1.8 and 2.4 Å resolution respectively. Deletion of 45 N-terminal residues (EhPSAT_Δ45) resulted in an inactive protein, the structure showed a dimeric arrangement drastically different from that of the wild-type protein, with the two monomers translated and rotated by almost 180° with respect to each other; causing a rearrangement of the active site to which PLP was unable to bind. Deletion of first N-terminal 15 (EhPSAT_Δ15) and four 11th to 14th residues (EhPSAT_Δ4) yielded up to 98% and 90% decrease in the activity respectively. Absence of aldimine linkage between PLP-Lys in the crystal structure of EhPSAT_Δ4 mutant explains for such decrease in activity and describes the importance of these N-terminal residues. Furthermore, a halide-binding site was found in close proximity to the active site. A stretch of six amino acids (146-NNTIYG-151) only conserved in the Entamoeba genus, contributes to halide binding may explain that the halide inhibition could be specific to Entamoeba.

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Organizational Affiliation: 

Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India.