8OY0 image
Entry Detail
PDB ID:
8OY0
Keywords:
Title:
ATP phosphoribosyltransferase (HisZG ATPPRT) from Acinetobacter baumanii
Biological Source:
PDB Version:
Deposition Date:
2023-05-03
Release Date:
2023-11-29
Method Details:
Experimental Method:
Resolution:
2.40 Å
R-Value Free:
0.26
R-Value Work:
0.23
R-Value Observed:
0.23
Space Group:
P 1 21 1
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:ATP phosphoribosyltransferase regulatory subunit
Chain IDs:A, B, C, D
Chain Length:389
Number of Molecules:4
Biological Source:Acinetobacter baumannii ATCC 17978
Polymer Type:polypeptide(L)
Description:ATP phosphoribosyltransferase
Chain IDs:E, F, G, H
Chain Length:228
Number of Molecules:4
Biological Source:Acinetobacter baumannii ATCC 17978
Primary Citation
Crystal Structure, Steady-State, and Pre-Steady-State Kinetics of Acinetobacter baumannii ATP Phosphoribosyltransferase.
Biochemistry 63 230 240 (2024)
PMID: 38150593 DOI: 10.1021/acs.biochem.3c00551

Abstact

The first step of histidine biosynthesis in Acinetobacter baumannii, the condensation of ATP and 5-phospho-α-d-ribosyl-1-pyrophosphate to produce N1-(5-phospho-β-d-ribosyl)-ATP (PRATP) and pyrophosphate, is catalyzed by the hetero-octameric enzyme ATP phosphoribosyltransferase, a promising target for antibiotic design. The catalytic subunit, HisGS, is allosterically activated upon binding of the regulatory subunit, HisZ, to form the hetero-octameric holoenzyme (ATPPRT), leading to a large increase in kcat. Here, we present the crystal structure of ATPPRT, along with kinetic investigations of the rate-limiting steps governing catalysis in the nonactivated (HisGS) and activated (ATPPRT) forms of the enzyme. A pH-rate profile showed that maximum catalysis is achieved above pH 8.0. Surprisingly, at 25 °C, kcat is higher when ADP replaces ATP as substrate for ATPPRT but not for HisGS. The HisGS-catalyzed reaction is limited by the chemical step, as suggested by the enhancement of kcat when Mg2+ was replaced by Mn2+, and by the lack of a pre-steady-state burst of product formation. Conversely, the ATPPRT-catalyzed reaction rate is determined by PRATP diffusion from the active site, as gleaned from a substantial solvent viscosity effect. A burst of product formation could be inferred from pre-steady-state kinetics, but the first turnover was too fast to be directly observed. Lowering the temperature to 5 °C allowed observation of the PRATP formation burst by ATPPRT. At this temperature, the single-turnover rate constant was significantly higher than kcat, providing additional evidence for a step after chemistry limiting catalysis by ATPPRT. This demonstrates allosteric activation by HisZ accelerates the chemical step.

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