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Direct visualization of critical hydrogen atoms in a pyridoxal 5'-phosphate enzyme.

ABSTRACT: Enzymes dependent on pyridoxal 5'-phosphate (PLP, the active form of vitamin B6) perform a myriad of diverse chemical transformations. They promote various reactions by modulating the electronic states of PLP through weak interactions in the active site. Neutron crystallography has the unique ability of visualizing the nuclear positions of hydrogen atoms in macromolecules. Here we present a room-temperature neutron structure of a homodimeric PLP-dependent enzyme, aspartate aminotransferase, which was reacted in situ with ?-methylaspartate. In one monomer, the PLP remained as an internal aldimine with a deprotonated Schiff base. In the second monomer, the external aldimine formed with the substrate analog. We observe a deuterium equidistant between the Schiff base and the C-terminal carboxylate of the substrate, a position indicative of a low-barrier hydrogen bond. Quantum chemical calculations and a low-pH room-temperature X-ray structure provide insight into the physical phenomena that control the electronic modulation in aspartate aminotransferase.Pyridoxal 5'-phosphate (PLP) is a ubiquitous co factor for diverse enzymes, among them aspartate aminotransferase. Here the authors use neutron crystallography, which allows the visualization of the positions of hydrogen atoms, and computation to characterize the catalytic mechanism of the enzyme.

SUBMITTER: Dajnowicz S

PROVIDER: S-EPMC5643538 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Direct visualization of critical hydrogen atoms in a pyridoxal 5'-phosphate enzyme.

Dajnowicz Steven S Johnston Ryne C RC Parks Jerry M JM Blakeley Matthew P MP Keen David A DA Weiss Kevin L KL Gerlits Oksana O Kovalevsky Andrey A Mueser Timothy C TC

Nature communications 20171016 1

Enzymes dependent on pyridoxal 5'-phosphate (PLP, the active form of vitamin B<sub>6</sub>) perform a myriad of diverse chemical transformations. They promote various reactions by modulating the electronic states of PLP through weak interactions in the active site. Neutron crystallography has the unique ability of visualizing the nuclear positions of hydrogen atoms in macromolecules. Here we present a room-temperature neutron structure of a homodimeric PLP-dependent enzyme, aspartate aminotransf ...[more]

PMID: 29038582

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Project description:The growing number of high-resolution crystal structures of large RNA molecules provides much information for understanding the principles of structural organization of these complex molecules. Several in-depth analyses of nucleobase-centered RNA structural motifs and backbone conformations have been published based on this information, including a systematic classification of base pairs by Leontis and Westhof. However, hydrogen bonds involving sugar-phosphate backbone atoms of RNA have not been analyzed systematically until recently, although such hydrogen bonds appear to be common both in local and tertiary interactions. Here we review some backbone structural motifs discussed in the literature and analyze a set of eight high-resolution multi-domain RNA structures. The analyzed RNAs are highly structured: among 5372 nucleotides in this set, 89% are involved in at least one "long-range" RNA-RNA hydrogen bond, i.e., hydrogen bonds between atoms in the same residue or sequential residues are ignored. These long-range hydrogen bonds frequently use backbone atoms as hydrogen bond acceptors, i.e., OP1, OP2, O2', O3', O4', or O5', or as a donor (2'OH). A surprisingly large number of such hydrogen bonds are found, considering that neither single-stranded nor double-stranded regions will contain such hydrogen bonds unless additional interactions with other residues exist. Among 8327 long-range hydrogen bonds found in this set of structures, 2811, or about one-third, are hydrogen bonds entailing RNA backbone atoms; they involve 39% of all nucleotides in the structures. The majority of them (2111) are hydrogen bonds entailing ribose hydroxyl groups, which can be used either as a donor or an acceptor; they constitute 25% of all hydrogen bonds and involve 31% of all nucleotides. The phosphate oxygens OP1 or OP2 are used as hydrogen bond acceptors in 12% of all nucleotides, and the ribose ring oxygen O4' and phosphodiester oxygens O3' and O5' are used in 4%, 4%, and 1% of all nucleotides, respectively. Distributions of geometric parameters and some examples of such hydrogen bonds are presented in this report. A novel motif involving backbone hydrogen bonds, the ribose-phosphate zipper, is also identified.

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Direct visualization of critical hydrogen atoms in a pyridoxal 5'-phosphate enzyme.

Publications

Direct visualization of critical hydrogen atoms in a pyridoxal 5'-phosphate enzyme.

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