6‐Pyruvoyl‐Tetrahydropterin Synthase

Abstract

The 6‐pyruvoyl‐tetrahydropterin synthase (PTPS), a zinc‐dependent, heat‐stable, homohexameric protein complex of approximately 90 kDa molecular weight catalyzes the conversion of dihydroneopterin triphosphate to 6‐pyruvoyl‐tetrahydropterin, the second of three enzymatic steps in the synthesis of tetrahydrobiopterin from GTP. The 6‐pyruvoyl‐tetrahydropterin synthetase monomer forms a compact, single‐domain α + β structure containing a sequential, four‐stranded, antiparallel β‐sheet. Oligomerization occurs through association of monomers via their β‐sheets that form a 12‐stranded β‐barrel structure that is duplicated in the functional hexameric form via a head‐to‐head association of two trimers. The PTPS active site is a 12‐Å deep cavity that is located on the interface of three monomers, two from one trimer and one subunit from the other trimer. The Zn(II) binding site is located at the center of the cavity. The transition metal is bound to the NE2 atoms of the three histidine residues. The role of the catalytic metal is to correctly position the substrate, to polarize the carbon–oxygen bonds for facile proton release from the substrate, and to prevent cleavage of the C1′‐C2′ substrate side‐chain bond. In addition, PTPS contains an intersubunit catalytic triad motif composed of the amino acid residues CysA42, HisB89, and AspB88 from two neighboring monomers (A and B) that putatively function as a relay system for proton abstraction from substrate and reaction intermediate. Residue GluA133 may represent the key residue for the stereospecificity of the catalyzed reaction.

Probing the Structural Dynamics of the Plasmodium falciparum Tunneling-Fold Enzyme 6-Pyruvoyl Tetrahydropterin Synthase to Reveal Allosteric Drug Targeting Sites

“…Specifically, we identified hinge sites that overlapped with residues of the active site: H29, H41, and H43 as well as E161. The functional importance of these residues was supported by previous studies in which the mutation of these residues resulted in either a complete or a dramatic loss of enzymatic activity (Bürgisser et al, 1995;Nar, 2011). Furthermore, the active residues were responsible for the coordination of the catalytically important FIGURE 12 | Color-coded representation of the PTPS structure based on the mobility of the residues within the (A) Low-frequency and (B) High-frequency GNM modes.…”

“…Residues E161 and T127, which are located at the bottom of the active site pocket (Figure 10A), showed significant fluctuation of the fast frequency modes, with E161 displaying the highest residue fluctuation ( Figure 9B). These two residues were previously reported for their key role in substrate recognition and binding, as they both act as proton donors and acceptors during catalysis (Nar et al, 1994;Bürgisser et al, 1995;Ploom et al, 1999;Nar, 2011). Furthermore, Nar and colleagues reported that T105, T106, and E107, located around the active site pocket, constitute an acceptor site for the substrate ring during catalysis in the Rattus norvegicus.…”

“…The trimers are 60 Å in diameter and have a height of 30 Å ( Nar et al, 1994 ). The structure of PTPS is characterized by a conically shaped central barrel that accumulates a cluster of basic and aromatic residues ( Nar, 2011 ). PTPS has six zinc-containing active sites, and each site is buried in a deep cavity of 12 Å formed between every three adjacent monomers ( Figure 1 ).…”