Characterization of porphobilinogen deaminase mutants reveals that arginine-173 is crucial for polypyrrole elongation mechanism

Characterization of porphobilinogen deaminase mutants reveals that arginine-173 is crucial for polypyrrole elongation mechanism

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Summary: Porphobilinogen deaminase (PBGD), the third enzyme in the heme biosynthesis, catalyzes the sequential coupling of four porphobilinogen (PBG) molecules into a heme precursor.Mutations in PBGD are associated with acute intermittent porphyria (AIP), a rare metabolic disorder.We used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to demonstrate that wild-type PBGD and AIP-associated mutant R167W both Bottle Teat existed as holoenzymes (Eholo) covalently attached to the dipyrromethane cofactor, and three intermediate complexes, ES, ES2, and ES3, where S represents PBG.In contrast, only ES2 was Option Switch Visor detected in AIP-associated mutant R173W, indicating that the formation of ES3 is inhibited.The R173W crystal structure in the ES2-state revealed major rearrangements of the loops around the active site, compared to wild-type PBGD in the Eholo-state.

These results contribute to elucidating the structural pathogenesis of two common AIP-associated mutations and reveal the important structural role of Arg173 in the polypyrrole elongation mechanism.