Affiliation:
1. Department of Chemistry, Indiana University, Bloomington, IN 47405
2. Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405
3. Laboratory for Biological Mass Spectrometry, Department of Chemistry, Indiana University, Bloomington, IN 47405
Abstract
In response to bacterial infection, the vertebrate host employs the metal-sequestering protein calprotectin (CP) to withhold essential transition metals, notably Zn(II), to inhibit bacterial growth. Previous studies of the impact of CP-imposed transition-metal starvation in
A. baumannii
identified two enzymes in the de novo biosynthesis pathway of queuosine-transfer ribonucleic acid (Q-tRNA) that become cellularly abundant, one of which is QueD2, a 6-carboxy-5,6,7,8-tetrahydropterin (6-CPH
4
) synthase that catalyzes the initial, committed step of the pathway. Here, we show that CP strongly disrupts Q incorporation into tRNA. As such, we compare the
Ab
QueD2 “low-zinc” paralog with a housekeeping, obligatory Zn(II)-dependent enzyme QueD. The crystallographic structure of Zn(II)-bound
Ab
QueD2 reveals a distinct catalytic site coordination sphere and assembly state relative to QueD and possesses a dynamic loop, immediately adjacent to the catalytic site that coordinates a second Zn(II) in the structure. One of these loop-coordinating residues is an invariant Cys18, that protects QueD2 from dissociation of the catalytic Zn(II) while maintaining flux through the Q-tRNA biosynthesis pathway in cells. We propose a “metal retention” model where Cys18 introduces coordinative plasticity into the catalytic site which slows metal release, while also enhancing the metal promiscuity such that Fe(II) becomes an active cofactor. These studies reveal a complex, multipronged evolutionary adaptation to cellular Zn(II) limitation in a key Zn(II) metalloenzyme in an important human pathogen.
Funder
HHS | NIH | National Institute of General Medical Sciences
Division of Intramural Research, National Institute of Allergy and Infectious Diseases
Publisher
Proceedings of the National Academy of Sciences
Cited by
2 articles.
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