Structural highlights
Publication Abstract from PubMedPhosphoserine 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 3.0A resolution and the structures of its mutants, EhPSAT_Delta45 and EhPSAT_Delta4, at 1.8 and 2.4A resolution respectively. Deletion of 45 N-terminal residues (EhPSAT_Delta45) 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 degrees 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_Delta15) and four 11th to 14th residues (EhPSAT_Delta4) yielded up to 98% and 90% decrease in the activity respectively. Absence of aldimine linkage between PLP-Lys in the crystal structure of EhPSAT_Delta4 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. N-terminal residues are crucial for quaternary structure and active site conformation for the phosphoserine aminotransferase from enteric human parasite E. histolytica.,Singh RK, Tomar P, Dharavath S, Kumar S, Gourinath S Int J Biol Macromol. 2019 Jul 1;132:1012-1023. doi:, 10.1016/j.ijbiomac.2019.04.027. Epub 2019 Apr 5. PMID:30959130[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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