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Capturing a Cryptic Biosynthetic Intermediate Reveals Novel Enzyme Functions in Molybdenum Cofactor Biosynthesis
Author(s) -
Yokoyama Kenichi,
Hover Bradley M.,
Tonthat Nam K.,
Schumacher Maria A.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.501.2
Subject(s) - molybdenum cofactor , gtp' , guanosine , biology , enzyme , guanosine triphosphate , biochemistry , cofactor , biosynthesis
The molybdenum cofactor (Moco) is essential for all kingdoms of life, plays central roles in various biological processes, and must be biosynthesized de novo . During Moco biosynthesis, the characteristic pyranopterin ring is constructed by a complex rearrangement of guanosine 5′‐triphosphate (GTP) into cyclic pyranopterin (cPMP) through the action of two enzymes, MoaA and MoaC. Conventionally, MoaA was considered to catalyze the majority of this transformation, with MoaC playing little or no role in the pyranopterin formation. However, the data from our lab suggest a distinct model, where MoaC is responsible for the majority of the transformation by converting an unusual cyclic nucleoside, 3′,8‐cyclo‐7,8‐dihydro‐guanosine 5′‐triphosphate (3′,8‐cH 2 GTP), to cPMP ( Fig. 1). In this talk, I will present our recent isolation and biochemical characterization of 3′,8‐cH 2 GTP and functional and X‐ray crystallographic characterizations of MoaA and MoaC. These studies revealed that 3′,8‐cH 2 GTP is the only product of MoaA that can be converted to cPMP by MoaC. Our structural studies captured the specific binding of 3′,8‐cH 2 GTP in the active‐site of MoaC ( Fig. 2). These observations provided strong evidence that the physiological function of MoaA is the conversion of GTP to 3′,8‐cH 2 GTP (GTP 3′,8‐cyclase), and that of MoaC is to catalyze the rearrangement of 3′,8‐cH 2 GTP into cPMP (cPMP synthase). Furthermore, our structure‐guided studies suggest that MoaC catalysis involves the dynamic motions of enzyme active‐site loops as a way to control the timing of interaction between the reaction intermediates and catalytically essential amino acid residues. Thus, these results reveal the novel mechanism behind Moco biosynthesis as well as providing mechanistic and structural insights into how enzymes catalyze complex rearrangement reactions. Support or Funding Information NIH R01 GM112838Proposed functions of MoaA and MoaC during Moco biosynthesis.X‐ray crystal structure of MoaC in complex with 3′,8‐cH 2 GTP.