Phe161 and Arg166 variants of p-hydroxybenzoate hydroxylase Implications for NADPH recognition and structural stability

AbstractPhe161 and Arg166 of p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens belong to a newly discovered sequence motif in flavoprotein hydroxylases with a putative dual function in FAD and NADPH binding [1]. To study their role in more detail, Phe161 and Arg166 were selectively changed by site-directed mutagenesis. F161A and F161G are catalytically competent enzymes having a rather poor affinity for NADPH. The catalytic properties of R166K are similar to those of the native enzyme. R166S and R166E show impaired NADPH binding and R166E has lost the ability to bind FAD. The crystal structure of substrate complexed F161A at 2.2 Å is indistinguishable from the native enzyme, except for small changes at the site of mutation. The crystal structure of substrate complexed R166S at 2.0 Å revealed that Arg166 is important for providing an intimate contact between the FAD binding domain and a long excursion of the substrate binding domain. It is proposed that this interaction is essential for structural stability and for the recognition of the pyrophosphate moiety of NADPH

X-ray christallographic studies on the enzymatic mechanism of p-Hydroxybenzoate Hydroxylase

Onderwerp van dit proefschrift is onderzoek met behulp van eiwitkristallografie en modelbouw naar het katalytisch mechanisme van het enzym p-hydroxybenzoate hydroxylase Uit Pseudomonas fluorescens. p-Hydroxybenzoate hydroxylase is een bacterieel enzym wat de inbouw van moleculaire zuurstof in een aromatisch substraat (p-hydroxybenzoaat) kataliseert: ... Zie: Samenvatting

The transfer of protein crystals from their original mother liquor to a solution with a completely different precipitant

A procedure is described for the transfer of protein crystals from an ammonium sulfate‐containing mother liquor to a solution with another precipitant, such as polyethylene glycol. The suitable concentration of the alternative precipitant is established via a novel protocol, using a hanging‐drop equilibration method. This crystal transfer procedure is illustrated by experiments with crystals of trypanosomal triosephosphate isomerase and bacterial p ‐hydroxybenzoate hydroxylase, but it might have more general applicability

Fractal Dimensions of Macromolecular Structures

Quantifying the properties of macromolecules is a prerequisite for understanding their roles in biochemical processes. One of the less-explored geometric features of macromolecules is molecular surface irregularity, or ‘roughness’, which can be measured in terms of fractal dimension (D). In this study, we demonstrate that surface roughness correlates with ligand binding potential. We quantified the surface roughnesses of biological macromolecules in a large-scale survey that revealed D values between 2.0 and 2.4. The results of our study imply that surface patches involved in molecular interactions, such as ligand-binding pockets and protein-protein interfaces, exhibit greater local fluctuations in their fractal dimensions than ‘inert’ surface areas. We expect approximately 22 % of a protein’s surface outside of the crystallographically known ligand binding sites to be ligandable. These findings provide a fresh perspective on macromolecular structure and have considerable implications for drug design as well as chemical and systems biology.ISSN:1868-1743ISSN:1868-175

Crystal structure of p-hydroxybenzoate hydroxylase complexed with its reaction product 3,4-dihydroxybenzoate

Crystals of the flavin-containing enzyme p-hydroxybenzoate hydroxylase (PHBHase) complexed with its reaction product were investigated in order to obtain insight into the catalytic cycle of this enzyme involving two substrates and two cofactors. PHBHase was crystallized initially with its substrate, p-hydroxybenzoate and the substrate was then converted into the product 3,4-dihydroxybenzoate by allowing the catalytic reaction to proceed in the crystals. In addition, crystals were soaked in mother liquor containing a high concentration of this product. Data up to 2.3 A (1 A = 0.1 nm) were collected by the oscillation method and the structure of the enzyme product complex was refined by alternate restrained least-squares procedures and model building by computer graphics techniques. A total of 273 solvent molecules could be located, four of them being presumably sulfate ions. The R-factor for 14,339 reflections between 6.0 A and 2.3 A is 19.3%. The 3-hydroxyl group of the product introduced by the enzyme is clearly visible in the electron density, showing unambiguously which carbon atom of the substrate is hydroxylated. A clear picture of the hydroxylation site is obtained. The plane of the product is rotated 21 degrees with respect to the plane of the substrate in the current model of enzyme-substrate complex. The 4-hydroxyl group of the product is hydrogen bonded to the hydroxyl group of Tyr201, its carboxyl group is interacting with the side-chains of Tyr222, Arg214 and Ser212, while the newly introduced 3-hydroxyl group makes a hydrogen bond with the backbone carbonyl oxygen of Pro293

Structure-based prediction of modifications in glutarylamidase to allow single-step enzymatic production of 7-aminocephalosporanic acid from cephalosporin C

Glutarylamidase is an important enzyme employed in the commercial production of 7-aminocephalosporanic acid, a starting compound in the synthesis of cephalosporin antibiotics. 7-aminocephalosporanic acid is obtained from cephalosporin C, a natural antibiotic, either chemically or by a two-step enzymatic process utilizing the enzymes D-amino acid oxidase and glutarylamidase. We have investigated possibilities for redesigning glutarylamidase for the production of 7-aminocephalosporanic acid from cephalosporin C in a single enzymatic step. These studies are based on the structures of glutarylamidase, which we have solved with bound phosphate and ethylene glycol to 2.5 Å resolution and with bound glycerol to 2.4 Å. The phosphate binds near the catalytic serine in a way that mimics the hemiacetal that develops during catalysis, while the glycerol occupies the side-chain binding pocket. Our structures show that the enzyme is not only structurally similar to penicillin G acylase but also employs essentially the same mechanism in which the α-amino group of the catalytic serine acts as a base. A subtle difference is the presence of two catalytic dyads, His B23/Glu B455 and His B23/Ser B1, that are not seen in penicillin G acylase. In contrast to classical serine proteases, the central histidine of these dyads interacts indirectly with the Oγ through a hydrogen bond relay network involving the α-amino group of the serine and a bound water molecule. A plausible model of the enzyme–substrate complex is proposed that leads to the prediction of mutants of glutarylamidase that should enable the enzyme to deacylate cephalosporin C into 7-aminocephalosporanic acid