Identification, soluble expression, and characterization of a novel endo-inulinase from Lipomyces starkeyi NRRL Y-11557

Insights in inulin binding and inulin oligosaccharide formation by novel multi domain endo-inulinases from Botrytis cinerea

World-wide, pathogenic fungi such as Botrytis cinerea cause tremendous yield losses in terms of food production and post-harvest food decay. Many fungi produce inulin-type oligosaccharides (IOSs) from inulin through endo-inulinases which typically show a two domain structure. B.cinerea lacks a two domain endo-inulinase but contains a three domain structure instead. Genome mining revealed three and four domain (d4) enzymes in the fungal kingdom. Here, three and two domain enzymes were compared in their capacity to produce IOSs from inulin. Hill kinetics were observed in three domain enzymes as compared to Michaelis-Menten kinetics in two domain enzymes, suggesting that the N-terminal extension functions as a carbohydrate binding module. Analysis of the IOS product profiles generated from purified GF6, GF12, GF16 and GF18 inulins and extensive sugar docking approaches led to enhanced insights in the active site functioning, revealing subtle differences between the endo-inulinases from Aspergillus niger and B. cinerea. Improved insights in structure-function relationships in fungal endo-inulinases offer opportunities to develop superior enzymes for the production of specific IOS formulations to improve plant and animal health (priming agents, prebiotics).

System analysis of Lipomyces starkeyi during growth on various plant-based sugars

Oleaginous yeasts have received significant attention due to their substantial lipid storage capability. The accumulated lipids can be utilized directly or processed into various bioproducts and biofuels. Lipomyces starkeyi is an oleaginous yeast capable of using multiple plant-based sugars, such as glucose, xylose, and cellobiose. It is, however, a relatively unexplored yeast due to limited knowledge about its physiology. In this study, we have evaluated the growth of L. starkeyi on different sugars and performed transcriptomic and metabolomic analyses to understand the underlying mechanisms of sugar metabolism. Principal component analysis showed clear differences resulting from growth on different sugars. We have further reported various metabolic pathways activated during growth on these sugars. We also observed non-specific regulation in L. starkeyi and have updated the gene annotations for the NRRL Y-11557 strain. This analysis provides a foundation for understanding the metabolism of these plant-based sugars and potentially valuable information to guide the metabolic engineering of L. starkeyi to produce bioproducts and biofuels. KEY POINTS: • L. starkeyi metabolism reprograms for consumption of different plant-based sugars. • Non-specific regulation was observed during growth on cellobiose. • L. starkeyi secretes β-glucosidases for extracellular hydrolysis of cellobiose.

Characterization of inulolytic enzymes from the Jerusalem artichoke-derived Glutamicibacter mishrai NJAU-1

The rhizosphere context of inulin-accumulating plants, such as Jerusalem artichoke (Helianthus tuberosus), is an ideal starting basis for the discovery of inulolytic enzymes with potential for bio fructose production. We isolated a Glutamicibacter mishrai NJAU-1 strain from this context, showing exo-inulinase activity, releasing fructose from fructans. The growth conditions (pH 9.0; 15 °C) were adjusted, and the production of inulinase by Glutamicibacter mishrai NJAU-1 increased by 90% (0.32 U/mL). Intriguingly, both levan and inulin, but not fructose and sucrose, induced the production of exo-inulinase activity. Two exo-inulinase genes (inu1 and inu2) were cloned and heterologously expressed in Pichia pastoris. While INU2 preferentially hydrolyzed longer inulins, the smallest fructan 1-kestose appeared as the preferred substrate for INU1, also efficiently degrading nystose and sucrose. Active site docking studies with GFn- and Fn-type small inulins (G is glucose, F is fructose, and n is the number of β (2-1) bound fructose moieties) revealed subtle substrate differences between INU1 and INU2. A possible explanation about substrate specificity and INU's protein structure is then suggested. KEY POINTS: • A Glutamicibacter mishrai strain harbored exo-inulinase activity. • Fructans induced the inulolytic activity in G. mishrai while the inulolytic activity was optimized at pH 9.0 and 15 °C. • Two exo-inulinases with differential substrate specificity were characterized.

Efficient production of inulo-oligosaccharides from inulin by exo- and endo-inulinase co-immobilized onto a self-assembling protein scaffold

Inulin can be hydrolyzed by inulinases to yield inulo-oligosaccharides (IOSs), which have great application potential in the food and nutraceutical industries. However, conventional enzymatic production of IOSs is limited by long hydrolysis times and poor thermo-stability of inulinases. Here, the self-assembling protein scaffold EutM was engineered to co-immobilize exo-inulinase (EXINU) and endo-inulinase (ENINU) for synergistic hydrolysis of inulin to produce IOSs with 3 to 5 monosaccharide units (DP3-5 IOSs). The immobilization of EXINU/ENINU onto the EutM scaffold resulted in an increase of catalytic efficiency, a 65% increase of the V_max of ENINU, as well as an increase of thermo-stability, with 4.26-fold higher residual activity of EXINU after 22 h-incubation at 50 °C. After optimization, two efficient production protocols were obtained, in which the yield and productivity of DP3-5 IOSs reached 80.38% and 70.86 g·(L·h)^-1, respectively, which were at a high level in similar studies. Overall, this study provides an attractive self-assembling protein platform for the co-immobilization of inulinases, as well as optimized bioprocesses with great promise for the industrial production of DP3-5 IOSs.

Recent Developments in Industrial Mycozymes: A Current Appraisal

Fungi, being natural decomposers, are the most potent, ubiquitous and versatile sources of industrial enzymes. About 60% of market share of industrial enzymes is sourced from filamentous fungi and yeasts. Mycozymes (myco-fungus; zymes-enzymes) are playing a pivotal role in several industrial applications and a number of potential applications are in the offing. The field of mycozyme production, while maintaining the old traditional methods, has also witnessed a sea change due to advents in recombinant DNA technology, optimisation protocols, fermentation technology and systems biology. Consolidated bioprocessing of abundant lignocellulosic biomass and complex polysaccharides is being explored at an unprecedented pace and a number of mycozymes of diverse fungal origins are being explored using suitable platforms. The present review attempts to revisit the current status of various mycozymes, screening and production strategies and applications thereof.

A Novel Inulin-Mediated Ethanol Precipitation Method for Separating Endo-Inulinase From Inulinases for Inulooligosaccharides Production From Inulin

Inulin is a kind of polysaccharide that can be obtained various biomass. Inulooligosaccharides (IOS), a kind of oligosaccharides that can be obtained from inulin by enzymatic hydrolysis using inulinases, have been regarded as the functional food ingredients. Commercially available inulinases produced by natural Aspergillus niger contained both endo- and exo-inulinase activities. For IOS production from inulin, it is desirable to use only endo-inulinase as exo-inulinase would produce mainly the monosacchairde fructose from inulin. In the present study, a simple inulin-mediated ethanol precipitation method was developed to separate endo- and exo-inulinases present in natural inulinases. IOS production from inulin using the enriched endo-inulinase was then optimized in process conditions including pH and temperature, achieving a high yield of ∼94%. The resultant IOS products had a degree of polymerization ranging from 2 to 7. The study demonstrated a novel method for obtaining partially purified or enriched endo-inulinase for IOS production from inulin in an efficient process.

Understanding the interactive influence of hydrolytic conditions on biocatalytic production of fructooligosaccharides from inulin

Statistical optimization of hydrolytic conditions for the production of fructooligosaccharides (FOSs) from pure inulin using Aspergillus tritici endoinulinase was carried out in a batch system. FOSs yield 99.19% was obtained under the optimized hydrolytic conditions i.e. inulin concentration (7.3%), enzyme load (65 IU), hydrolysis time (13 h) and agitation (100 rpm). The closeness of value of co-efficient of determination (R²) to 1, good agreement between model's predicted and experimental values, low percentage error (<5%), high adequate precision (>4%) and F value (11,634.32), and low Lack of fit (0.60) of the designed model authenticates its fitness. High substrate concentration, low enzyme load and short hydrolysis span justifies efficiency of developed process for the preparation of FOSs from inulin using fungal endoinulinase. TLC chromatographic and densitometry studies confirmed the synthesis of short-chain length FOSs. FOSs preparation contained 33.85% GF2 (ketose), 24.50% GF3 (nystose), 7.26% GF4 (fructofuranosylnystose) and 33.58% FOSs of DP5-9.

Characterization of a Maltase from an Early-Diverged Non-Conventional Yeast Blastobotrys adeninivorans

Genome of an early-diverged yeast Blastobotrys (Arxula) adeninivorans (Ba) encodes 88 glycoside hydrolases (GHs) including two α-glucosidases of GH13 family. One of those, the rna_ARAD1D20130g-encoded protein (BaAG2; 581 aa) was overexpressed in Escherichia coli, purified and characterized. We showed that maltose, other maltose-like substrates (maltulose, turanose, maltotriose, melezitose, malto-oligosaccharides of DP 4‒7) and sucrose were hydrolyzed by BaAG2, whereas isomaltose and isomaltose-like substrates (palatinose, α-methylglucoside) were not, confirming that BaAG2 is a maltase. BaAG2 was competitively inhibited by a diabetes drug acarbose (Ki = 0.8 µM) and Tris (Ki = 70.5 µM). BaAG2 was competitively inhibited also by isomaltose-like sugars and a hydrolysis product-glucose. At high maltose concentrations, BaAG2 exhibited transglycosylating ability producing potentially prebiotic di- and trisaccharides. Atypically for yeast maltases, a low but clearly recordable exo-hydrolytic activity on amylose, amylopectin and glycogen was detected. Saccharomyces cerevisiae maltase MAL62, studied for comparison, had only minimal ability to hydrolyze these polymers, and its transglycosylating activity was about three times lower compared to BaAG2. Sequence identity of BaAG2 with other maltases was only moderate being the highest (51%) with the maltase MalT of Aspergillus oryzae.