Role of an electrostatic network of residues in the enzymatic action of the Rhizomucor miehei lipase family

Combination of site-directed mutagenesis and yeast surface display enhances Rhizomucor miehei lipase esterification activity in organic solvent

To increase the activity of Rhizomucor miehei lipase (RML) in organic solvent, multiple sequence alignments and rational site-directed mutagenesis were used to create RML variants. The obtained proteins were surface-displayed on Pichia pastoris by fusion to Flo1p as an anchor protein. The synthetic activity of four variants showed from 1.1- to 5-fold the activity of native lipase in an esterification reaction in heptane with alcohol and caproic acid as substrates. The increase in esterification activity may be attributed to the four mutations changing the flexibility of RML or facilitating the reaction. In conclusion, this method demonstrated that multiple sequence alignments and rational site-directed mutagenesis combined with yeast display technology is a faster and more effective means of obtaining high-efficiency esterification lipase variants compared with previous similar methods.

Production of extracellular lipases by Rhizopus oligosporus in a stirred fermentor

The present investigation deals with the kinetics of submerged extracellular lipases fermentation by both wild and mutant strains of Rhizopus oligosporus var.microsporus in a laboratory scale stirred fermentor. Other parameters studied were inoculum size, pH, agitation and rate of aeration. It was found that the growth and lipases production was increased gradually and reached its maximum 9.07± 0.42(a) U mL(-1) (W) and 42.49 ± 3.91(a) U mL(-1) (M) after 30h of fermentation for both wild and mutant strain. There is overall increase of 109% (W) and 124% (M) in the production of extracellular lipases as compared to shake flask. Another significant finding of the present study is that the fermentation period is reduced to 30 h in case of wild and 23 h in case of mutant from 48 h in shake flask studies. The specific productivity of mutant strain (qp = 377.3 U/g cells/h) was several folds higher than wild strain. The specific production rate and growth coefficient revealed the hyperproducibility of extracellular lipases using mutant IIB-63NTG-7.

Creation of Rhizopus oryzae lipase having a unique oxyanion hole by combinatorial mutagenesis in the lid domain

Combinatorial libraries of the lid domain of Rhizopus oryzae lipase (ROL; Phe88Xaa, Ala91Xaa, Ile92Xaa) were displayed on the yeast cell surface using yeast cell-surface engineering. Among the 40,000 transformants in which ROL mutants were displayed on the yeast cell surface, ten clones showed clear halos on soybean oil-containing plates. Among these, some clones exhibited high activities toward fatty acid esters of fluorescein and contained non-polar amino acid residues in the mutated positions. Computer modeling of the mutants revealed that hydrophobic interactions between the substrates and amino acid residues in the open form of the lid might be critical for ROL activity. Based on these results, Thr93 and Asp94 were further combinatorially mutated. Among 6,000 transformants, the Thr93Thr, Asp94Ser and Thr93Ser, Asp94Ser transformants exhibited a significant shift in substrate specificity toward a short-chain substrate. Computer modeling of these mutants suggested that a unique oxyanion hole, which is composed of Thr85 Ogamma and Ser94 Ogamma, was formed and thus the substrate specificity was changed. Therefore, coupling combinatorial mutagenesis with the cell surface display of ROL could lead to the production of a unique ROL mutant.

Charged amino acids of the N-terminal domain are involved in coupling binding and gating in alpha7 nicotinic receptors

Binding of agonists to nicotinic acetylcholine receptors generates a sequence of conformational changes resulting in channel opening. Previously, we have shown that the aspartate residue Asp-266 at the M2-M3 linker of the alpha7 nicotinic receptor is involved in connecting binding and gating. High resolution structural data suggest that this region could interact with the so-called loops 2 and 7 of the extracellular N-terminal region. In this case, certain charged amino acids present in these loops could integrate together with Asp-266 and other amino acids, a mechanism involved in channel activation. To test this hypothesis, all charged residues in these loops, Asp-42, Asp-44, Glu-45, Lys-46, Asp-128, Arg-130, and Asp-135, were substituted with other amino acids, and expression levels and electrophysiological responses of mutant receptors were determined. Mutants at positions Glu-45, Lys-46, and Asp-135 exhibited poor or null functional responses to different nicotinic agonists regardless of significant membrane expression, whereas D128A showed a gain of function effect. Because the double reverse charge mutant K46D/D266K did not restore receptor function, a gating mechanism controlled by the pairwise electrostatic interaction between these residues is not likely. Rather, a network of interactions formed by residues Lys-46, Asp-128, Asp-135, Asp-266, and possibly others appears to link agonist binding to channel gating.

EF loop conformational change triggers ligand binding in beta-lactoglobulins

Beta-lactoglobulins, belonging to the lipocalin family, are a widely studied group of proteins, characterized by the ability to solubilize and transport hydrophobic ligands, especially fatty acids. Despite many reports, the mechanism of ligand binding and the functional role of these proteins is still unclear, and many contradicting concepts are often encountered in the literature. In the present paper the comparative analysis of the binding properties of beta-lactoglobulins has been performed using sequence-derived information, structure-based electrostatic calculations, docking simulations, and NMR experiments. Our results reveal for the first time the mechanism of beta-lactoglobulin ligand binding, which is completely determined by the opening-closing of EF loop, triggered by Glu89 protonation. The alkaline shift observed for Glu89 pKa in porcine beta-lactoglobulin (pKa 9.7) with respect to the bovine species (pKa 5.5) depends upon the interplay of electrostatic effects of few nearby key residues. Porcine protein is therefore able to bind fatty acids provided that the appropriate pH solution conditions are met (pH > 8.6), where the EF loop conformational change can take place. The unusually high pH of binding detected for porcine beta-lactoglobulin seems to be functional to lipases activity. Theoretical pKa calculations extended to representative beta-lactoglobulins allowed the identification of key residues involved in structurally and functionally important electrostatic interactions. The results presented here provide a strong indication that the described conformational change is a common feature of all beta-lactoglobulins.

The application of PCR for the isolation of a lipase gene from the genomic DNA of an Antarctic microfungus

We successfully isolated a lipase gene (designated lipPA) directly from the genomic DNA of an Antarctic isolate of Penicillium allii using PCR and a suite of degenerate primers specifically designed to target two conserved regions of fungal lipase genes. We applied the biolistic transformation system to successfully integrate the lipPA gene into a heterologous fungal host, Trichoderma reesei, one of the most powerful secretors of extracellular proteins, and induced the transformant to secrete an active lipase into the growth medium. The recombinant lipase had a temperature optimum of 25 degrees C at pH 7.9 and retained greater than 50% of the maximum activity from 10 degrees C to 35 degrees C and over a pH range from 4.0 to 8.5.

Long-chain fatty acyl-CoA esters induce lipase activation in the absence of a water-lipid interface

In most lipases a mobile element or lid domain covers the catalytic site of the enzyme and the lid opening event, which usually proceed at a lipid-water interface, is required to form the catalytically competent lipase. We report here a noticeable increase in activity of two fungal lipases assayed in aqueous solution in absence of any interface when adding submicellar concentrations of amphipathic physiological molecules like long-chain acyl-CoAs. The catalytic activity was dramatically dependent on the acyl chain length of the amphiphile and could be related with a lid-opening process. Our data support that lipase activation can be triggered in the absence of a well-defined interface, and stresses the notion that other non-aggregated amphipathic constituents of the local microenvironment can act as putative regulators of lipase activity.

Cloning of an alkaline lipase gene from Penicillium cyclopium and its expression in Escherichia coli

The gene encoding an alkaline lipase of Penicillium cyclopium PG37 was cloned with four steps of PCR amplification based on different principles. The cloned gene was 1,480 nucleotides in length, consisted of 94 bp of promoter region, and had 6 exons and 5 short introns ranging from 50 to 70 nucleotides. The open reading frame encoded a protein of 285 amino acid residues consisting of a 27-AA signal peptide and a 258-AA mature peptide, with a conserved motif of Gly-X-Ser-X-Gly shared by all types of alkaline lipases. However, this protein had a low homology with lipases of P. camembertii (22.9%), Humicola lanuginosa (25.6%), and Rhizomucor miehei (22.3%) at the amino acid level. The mature peptide-encoding cDNA was cloned and expressed in Escherichia coli on pET-30a for confirmation. A distinct band with a M.W. of 33 kDa was detected on SDS-PAGE. Results of a Western blot analysis and an enzyme activity assay verified the recombinant 33-kDa protein as an alkaline lipase. Its catalytic properties were not changed when compared with its natural counterpart.

Effect of the lipid interface on the catalytic activity and spectroscopic properties of a fungal lipase

Lipase from the fungi Thermomyces (formerly Humicola) lanuginosa (TlL) is widely used in industry. This interfacial enzyme is inactive under aqueous conditions, but catalytic activation is induced on binding to a lipid-water interface. In order for protein engineering to design more efficient mutants of TlL for specific applications, it is important to characterize its interfacial catalysis. A complete analysis of steady-state kinetics for the hydrolysis of a soluble substrate by TlL has been developed using an interface different from the substrate. Small vesicles of 1-palmitoyl-2-oleoylglycero-sn-3-phosphoglycerol (POPG) or other anionic phospholipids are a neutral diluent interface for the partitioning of substrate and enzyme. TlL binds to these interfaces in an active or open form, thus implying a displacement of the helical lid away from the active site. A study of the influence of substrate and diluent concentration dependence of the rate of hydrolysis provides a basis for the determination of the primary interfacial catalytic parameters. The interfacial activation is not supported by zwitterionic vesicles or by large anionic vesicles of 100 nm diameter, although TlL binds to these interfaces. Using a combination of fluorescence-based techniques applied to several mutants of TlL with different tryptophan residues we have shown that TlL binds to phospholipid vesicles in different forms rendering different catalytic activities, and that the open lid conformation is achieved and stabilized by a combination of electrostatic and hydrophobic interactions between the enzyme's lipid-binding face and the interface.