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Crystal structure of tryptophan synthase from Chlamydia trachomatis D/UW-3/CXCrystal structure of tryptophan synthase from Chlamydia trachomatis D/UW-3/CX
Structural highlights
FunctionTRPA_CHLTR The alpha subunit is responsible for the aldol cleavage of indoleglycerol phosphate to indole and glyceraldehyde 3-phosphate. Publication Abstract from PubMedIntracellular growth and pathogenesis of Chlamydia species is controlled by the availability of tryptophan, yet the complete biosynthetic pathway for l-Trp is absent among members of the genus. Some representatives, however, preserve genes encoding tryptophan synthase, TrpAB - a bifunctional enzyme catalyzing the last two steps in l-Trp synthesis. TrpA (subunit alpha) converts indole-3-glycerol phosphate into indole and glyceraldehyde-3-phosphate (alpha reaction). The former compound is subsequently used by TrpB (subunit beta) to produce l-Trp in the presence of l-Ser and a pyridoxal 5'-phosphate cofactor (beta reaction). Previous studies have indicated that in Chlamydia, TrpA has lost its catalytic activity yet remains associated with TrpB to support the beta reaction. Here, we provide detailed analysis of the TrpAB from C. trachomatis D/UW-3/CX, confirming that accumulation of mutations in the active site of TrpA renders it enzymatically inactive, despite the conservation of the catalytic residues. We also show that TrpA remains a functional component of the TrpAB complex, increasing the activity of TrpB by four-fold. The side chain of non-conserved betaArg267 functions as cation effector, potentially rendering the enzyme less susceptible to the solvent ion composition. The observed structural and functional changes detected herein were placed in a broader evolutionary and genomic context, allowing identification of these mutations in relation to their trp gene contexts in which they occur. Moreover, in agreement with the in vitro data, partial relaxation of purifying selection for TrpA, but not for TrpB, was detected, reinforcing a partial loss of TrpA functions during the course of evolution. Catalytically impaired TrpA subunit of tryptophan synthase from Chlamydia trachomatis is an allosteric regulator of TrpB.,Michalska K, Wellington S, Maltseva N, Jedrzejczak R, Selem-Mojica N, Rosas-Becerra LR, Barona-Gomez F, Hung DT, Joachimiak A Protein Sci. 2021 Sep;30(9):1904-1918. doi: 10.1002/pro.4143. Epub 2021 Jun 16. PMID:34107106[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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