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Structural basis for tetrapyrrole coordination by uroporphyrinogen decarboxylase
Author(s) -
Phillips John D.,
Whitby Frank G.,
Kushner James P.,
Hill Christopher P.
Publication year - 2003
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdg606
Subject(s) - decarboxylation , chemistry , tetrapyrrole , stereochemistry , carboxylate , uroporphyrinogen iii decarboxylase , residue (chemistry) , oxidoreductase , heme , active site , catalysis , enzyme , organic chemistry
Uroporphyrinogen decarboxylase (URO‐D), an essential enzyme that functions in the heme biosynthetic pathway, catalyzes decarboxylation of all four acetate groups of uroporphyrinogen to form coproporphyrinogen. Here we report crystal structures of URO‐D in complex with the I and III isomer coproporphyrinogen products. Crystallization required use of a novel enzymatic approach to generate the highly oxygen‐sensitive porphyrinogen substrate in situ . The tetrapyrrole product adopts a domed conformation that lies against a collar of conserved hydrophobic residues and allows formation of hydrogen bonding interactions between a carboxylate oxygen atom of the invariant Asp86 residue and the pyrrole NH groups. Structural and biochemical analyses of URO‐D proteins mutated at Asp86 support the conclusion that this residue makes important contributions to binding and likely promotes catalysis by stabilizing a positive charge on a reaction intermediate. The central coordination geometry of Asp86 allows the initial substrates and the various partially decarboxylated intermediates to be bound with equivalent activating interactions, and thereby explains how all four of the substrate acetate groups can be decarboxylated at the same catalytic center.