5KF6: Structure of proline utilization A from Sinorhizobium meliloti complexed with L-tetrahydrofuroic acid and NAD+ in space group P21

Aldehyde dehydrogenases (ALDHs) catalyze the NAD(P)+-dependent oxidation of aldehydes to carboxylic acids and are important for metabolism and detoxification. Although the ALDH superfamily fold is well established, some ALDHs contain an uncharacterized domain of unknown function (DUF) near the C terminus of the polypeptide chain. Herein, we report the first structure of a protein containing the ALDH superfamily DUF. Proline utilization A from Sinorhizobium meliloti (SmPutA) is a 1233-residue bifunctional enzyme that contains the DUF in addition to proline dehydrogenase and l-glutamate-gamma-semialdehyde dehydrogenase catalytic modules. Structures of SmPutA with a proline analog bound to the proline dehydrogenase site and NAD+ bound to the ALDH site were determined in two space groups at 1.7-1.9 A resolution. The DUF consists of a Rossmann dinucleotide-binding fold fused to a three-stranded beta-flap. The Rossmann domain resembles the classic ALDH superfamily NAD+-binding domain, whereas the flap is strikingly similar to the ALDH superfamily dimerization domain. Paradoxically, neither structural element performs its implied function. Electron density maps show that NAD+ does not bind to the DUF Rossmann fold, and small-angle X-ray scattering reveals a novel dimer that has never been seen in the ALDH superfamily. The structure suggests that the DUF is an adapter domain that stabilizes the aldehyde substrate binding loop and seals the substrate-channeling tunnel via tertiary structural interactions that mimic the quaternary structural interactions found in non-DUF PutAs. Kinetic data for SmPutA indicate a substrate-channeling mechanism, in agreement with previous studies of other PutAs.
PDB ID: 5KF6Download
MMDB ID: 143786
PDB Deposition Date: 2016/6/12
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Similar Structures:
Biological Unit for 5KF6: monomeric; determined by author
Molecular Components in 5KF6
Label Count Molecule
Protein (1 molecule)
Bifunctional Protein Puta
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

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