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Title: Catalytically impaired TrpA subunit of tryptophan synthase from Chlamydia trachomatis is an allosteric regulator of TrpB

Journal Article · · Protein Science
DOI:https://doi.org/10.1002/pro.4143· OSTI ID:1797338
 [1];  [2];  [3];  [3];  [4];  [4]; ORCiD logo [4];  [2]; ORCiD logo [5]
  1. Center for Structural Genomics of Infectious Diseases University of Chicago Chicago Illinois USA, Structural Biology Center, X‐ray Science Division Argonne National Laboratory Argonne Illinois USA
  2. Department of Genetics, Broad Institute of MIT and Harvard Cambridge Massachusetts USA
  3. Center for Structural Genomics of Infectious Diseases University of Chicago Chicago Illinois USA
  4. Evolution of Metabolic Diversity Laboratory Unidad de Genómica Avanzada (Langebio) Cinvestav Mexico
  5. Center for Structural Genomics of Infectious Diseases University of Chicago Chicago Illinois USA, Structural Biology Center, X‐ray Science Division Argonne National Laboratory Argonne Illinois USA, Department of Biochemistry and Molecular Biology University of Chicago Chicago Illinois USA
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Abstract Intracellular 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 α) converts indole‐3‐glycerol phosphate into indole and glyceraldehyde‐3‐phosphate (α reaction). The former compound is subsequently used by TrpB (subunit β) to produce l‐ Trp in the presence of l‐ Ser and a pyridoxal 5′‐phosphate cofactor (β reaction). Previous studies have indicated that in Chlamydia , TrpA has lost its catalytic activity yet remains associated with TrpB to support the β 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 βArg267 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.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER); National Institutes of Health (NIH); Royal Society United Kingdom; Consejo Nacional de Ciencia y Tecnología in Mexico (CONACyT)
Grant/Contract Number:
AC02-06CH11357; HHSN272201200026C; HHSN272201700060C; NAF\R2\180631; 285746
OSTI ID:
1797338
Alternate ID(s):
OSTI ID: 1797342; OSTI ID: 1831424
Journal Information:
Protein Science, Journal Name: Protein Science Vol. 30 Journal Issue: 9; ISSN 0961-8368
Publisher:
Wiley Blackwell (John Wiley & Sons)Copyright Statement
Country of Publication:
United Kingdom
Language:
English

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59 BASIC BIOLOGICAL SCIENCES
allosteric regulation
biosynthesis
catalysis
crystal structure
tryptophan