The N-linked oligosaccharide at Fc gamma RIIIa Asn-45: an inhibitory element for high Fc gamma RIIIa binding affinity to IgG glycoforms lacking core fucosylation.

Human leukocyte receptor IIIa (Fc gamma RIIIa) plays an important role in mediating therapeutic antibodies' antibody-dependent cellular cytotoxicity (ADCC), which is closely related to the clinical efficacy of anticancer processes in humans in vivo. The removal of the core fucose from oligosaccharides attached to the Fc region of antibodies improves Fc gamma RIIIa binding, allowing the antibodies to enhance dramatically the antibody effector functions of ADCC. In this study, the contribution of Fc gamma RIIIa oligosaccharides to the strength of the Fc gamma RIIIa/antibody complex was analyzed using a serial set of soluble human recombinant Fc gamma RIIIa lacking the oligosaccharides. A nonfucosylated antibody IgG1 appeared to have a significantly higher affinity to the wild-type Fc gamma RIIIa fully glycosylated at its five N-linked oligosaccharide sites than did the fucosylated IgG1, and this increased binding was almost abolished once all of the Fc gamma RIIIa glycosylation was removed. Our gain-of-function analysis in the Fc gamma RIIIa oligosaccharide at Asn-162 (N-162) confirmed that N-162 is the element required for the high binding affinity to nonfucosylated antibodies, as previously revealed by loss-of-function analyses. Interestingly, beyond our expectation, the Fc gamma RIIIa modified by N-162 alone showed a significantly higher binding affinity to nonfucosylated IgG1 than did the wild-type Fc gamma RIIIa. Attachment of the other four oligosaccharides, especially the Fc gamma RIIIa oligosaccharide at Asn-45 (N-45), hindered the high binding affinity of Fc gamma RIIIa to nonfucosylated IgG1. Our data clearly demonstrated that N-45 is an inhibitory element for the high Fc gamma RIIIa binding affinity mediated by N-162 to nonfucosylated antibodies. This information can be exploited for the structural-based functional study of Fc gamma RIIIa.

A novel catalytic ability of gamma-glutamylcysteine synthetase of Escherichia coli and its application in theanine production.

Gamma-glutamylcysteine synthetase (gammaGCS, EC 6.3.2.2) catalyzes the formation of gamma-glutamylcysteine from L-glutamic acid (Glu) and L-cysteine (Cys) in an ATP-dependent manner. While gammaGCS can use various amino acids as substrate, little is known about whether it can use non-amino acid compounds in place of Cys. We determined that gammaGCS from Escherichia coli has the ability to combine Glu and amines to form gamma-glutamylamides. The reaction rate depended on the length of the methylene chain of the amines in the following order: n-propylamine > butylamine > ethylamine >> methylamine. The optimal pH for the reaction was narrower and more alkaline than for the reaction with an amino acid. The newly found catalytic ability of gammaGCS was used in the production of theanine (gamma-glutamylethylamine). The resting cells of E. coli expressing gammaGCS, in which ATP was regenerated through glycolysis, synthesized 12.1 mM theanine (18 h) from 429 mM ethylamine.

YCM1008A, a novel Ca2+-signaling inhibitor, produced by Fusarium sp. YCM1008.

In the course of screening for drugs that suppress the Ca(2+)-mediated growth inhibition in a yeast mutant, we found that the metabolite of Fusarium sp. strain YCM1008 inhibited Ca(2+)-signaling. A novel pyrano-pyridone, YCM1008A was isolated from the fermentation broth using HLB column chromatography followed by HPLC, and the structure was elucidated by spectral analysis. YCM1008A suppressed Ca(2+)-induced growth inhibition of the Saccharomyces cerevisiae (Deltazds1Deltasyr1) mutant.

Fucose depletion from human IgG1 oligosaccharide enhances binding enthalpy and association rate between IgG1 and FcgammaRIIIa.

Depletion of fucose from human IgG1 oligosaccharide improves its affinity for Fcgamma receptor IIIa (FcgammaRIIIa). This is the first case where a glycoform modification is shown to improve glycoprotein affinity for the receptors without carbohydrate-binding capacity, suggesting a novel glyco-engineering strategy to improve ligand-receptor binding. To address the mechanisms of affinity improvement by the fucose depletion, we used isothermal titration calorimetry (ITC) and biosensor analysis with surface plasmon resonance. ITC demonstrated that IgG1-FcgammaRIIIa binding was driven by favorable binding enthalpy (DeltaH) but opposed by unfavorable binding entropy change (DeltaS). Fucose depletion from IgG1 enhanced the favorable DeltaH, leading to the increase in the binding constant of IgG1 for the receptor by a factor of 20-30. The increase in the affinity was mainly attributed to an enhanced association rate. A triple amino acid substitution in IgG1, S298A/E333A/K334A, is also known to improve IgG1 affinity for FcgammaRIIIa. ITC demonstrated that the amino acid substitution attenuated the unfavorable DeltaS resulting in a three- to fourfold increase in the binding constant. The affinity enhancement by the amino acid substitution was due to a reduced dissociation rate. These results indicate that the mechanism of affinity improvement by the fucose depletion is quite distinct from that by the amino acid substitution. Defucosylated IgG1 exhibited higher antibody-dependent cellular cytotoxicity (ADCC) than S298A/E333A/K334A-IgG1, showing a correlation between IgG1 affinity for FcgammaRIIIa and ADCC. We also examined the effect of FcgammaRIIIa polymorphism (Val158/Phe158) on IgG1-FcgammaRIIIa binding. The Phe to Val substitution increased FcgammaRIIIa affinity for IgG1 in an enthalpy-driven manner with the reduced dissociation rate. These results together highlight the distinctive functional improvement of affinity by IgG1 defucosylation and suggest that engineering of non-interfacial monosaccharides can improve glycoprotein affinity for receptors via an enthalpy-driven and association rate-assisted mechanism.

A novel gnd mutation leading to increased L-lysine production in Corynebacterium glutamicum.

Toward more efficient L-lysine production, we have been challenging genome-based strain breeding by the approach of assembling only relevant mutations in a single wild-type background. Following the creation of a new L-lysine producer Corynebacterium glutamicum AHP-3 that carried three useful mutations (lysC311, hom59, and pyc458) on the relevant downstream pathways, we shifted our target to the pentose phosphate pathway. Comparative genomic analysis for the pathway between a classically derived L-lysine producer and its parental wild-type identified several mutations. Among these mutations, a Ser-361-->Phe mutation in the 6-phosphogluconate dehydrogenase gene (gnd) was defined as a useful mutation for L-lysine production. Introduction of the gnd mutation into strain AHP-3 by allelic replacement led to approximately 15% increased L-lysine production. Enzymatic analysis revealed that the mutant enzyme was less sensitive than the wild-type enzyme to allosteric inhibition by intracellular metabolites, such as fructose 1,6-bisphosphate, D-glyceraldehyde 3-phosphate, phosphoribosyl pyrophosphate, ATP, and NADPH, which were known to inhibit this enzyme. Isotope-based metabolic flux analysis demonstrated that the gnd mutation resulted in 8% increased carbon flux through the pentose phosphate pathway during L-lysine production. These results indicate that the gnd mutation is responsible for diminished allosteric regulation and contributes to redirection of more carbon to the pentose phosphate pathway that was identified as the primary source for NADPH essential for L-lysine biosynthesis, thereby leading to improved product formation.

Comparison of biological activity among nonfucosylated therapeutic IgG1 antibodies with three different N-linked Fc oligosaccharides: the high-mannose, hybrid, and complex types.

The structure of asparagine-linked oligosaccharides attached to the antibody constant region (Fc) of human immunoglobulin G1 (IgG1) has been shown to affect the pharmacokinetics and antibody effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). However, it is still unclear how differences in the N-linked oligosaccharide structures impact the biological activities of antibodies, especially those lacking core fucose. Here, we succeeded in generating core fucose-lacking human IgG1 antibodies with three different N-linked Fc oligosaccharides, namely, a high-mannose, hybrid, and complex type, using the same producing clone, and compared their activities. Cultivation of an alpha-1,6-fucosyltransferase (FUT8) knockout Chinese hamster ovary cell line in the presence or absence of a glycosidase inhibitor (either swainsonine or kifunensine) yielded antibody production of each of the three types without contamination by the others. Two of three types of nonnaturally occurring atypical oligosaccharide IgG1, except the complex type, reduced the affinity for both human lymphocyte receptor IIIa (FcgammaRIIIa) and the C1q component of the complement, resulting in reduction of ADCC and CDC. The bulky structure of the nonreducing end of N-linked Fc oligosaccharides is considered to contribute the CDC change, whereas the structural change in the reducing end, i.e. the removal of core fucose, causes ADCC enhancement through improved FcgammaRIIIa binding. In the pharmacokinetic profile, although no significant difference of human neonatal Fc receptor (FcRn)-binding affinity was observed among the three types, the complex type showed longer serum half-lives than the other types irrespective of core fucosylation in mice, which also suggests the contribution of the nonreducing end structure. The present study provides basic information on the effects of core fucose-lacking N-linked Fc oligosaccharides on antibody biological activities.

Accumulation of anthranilic acid and N-glucosylanthranilic acid by a Corynebacterium glutamicum mutant resistant to DL-serine hydroxamate.

During a study on the effect of DL-serine hydroxamate on Corynebacterium glutamicum (JCM1318, a wild strain), a mutant resistant to the drug, strain TO3002, was isolated. This mutant accumulated five Ehrlich's reagent positive fluorescent substances in the culture medium. Two major and one minor fluorescent products were isolated by preparative high-performance liquid chromatography following charcoal column chromatography from the culture supernatant. One major product was identified as anthranilic acid whose molecular ion was confirmed to be 137 by a measurement of liquid chromatography-mass spectrometry (LC-MS), and NMR spectrum coincided with that of anthranilic acid. LC-MS spectra of another major and the minor product showed that they had the same molecular weight of 299. This major product was supported to be N-glucosylanthranilic acid (N-o-carboxyphenyl-1-beta-glucosylamine) by two-dimensional (1)H and (13)C NMR analyses. The minor product was speculated to be an Amadori compound derived from N-glucosylanthranilic acid. N-Glucosylanthranilic acid accumulated in the early phase, then decreased in the late phase of the culture. In contrast, the accumulation of anthranilic acid increased remarkably in the late phase of the fermentation. Based on this phenomenon, it was assumed that N-glucosylanthranilic acid once accumulated was decomposed to form anthranilic acid, at least in large part, with the progress of fermentation. The strain TO3002 showed a leaky requirement for L-tryptophan or indole (but did not for anthranilic acid) and resistance to DL-serine hydroxamate.