Biochemical Characterization of a Bifunctional Enzyme Constructed by the Fusion of a Glucuronan Lyase and a Chitinase from Trichoderma Sp
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life Article Biochemical Characterization of a Bifunctional Enzyme Constructed by the Fusion of a Glucuronan Lyase and a Chitinase from Trichoderma sp. Zeineb Baklouti 1,2 ,Cédric Delattre 1,3 , Guillaume Pierre 1 , Christine Gardarin 1, Slim Abdelkafi 2 , Philippe Michaud 1 and Pascal Dubessay 1,* 1 CNRS, SIGMA Clermont, Institut Pascal, Université Clermont-Auvergne, FS-63000 Clermont-Ferrand, France; [email protected] (Z.B.); [email protected] (C.D.); [email protected] (G.P.); [email protected] (C.G.); [email protected] (P.M.) 2 Département Génie Biologique, Université de Sfax, Unité de Biotechnologie des Algues, Ecole National d’Ingénieurs de Sfax, 3018 Sfax, Tunisia; slim.abdelkafi@enis.tn 3 Institut Universitaire de France (IUF), 1 rue Descartes, 75005 Paris, France * Correspondence: [email protected] Received: 16 September 2020; Accepted: 6 October 2020; Published: 8 October 2020 Abstract: Bifunctional enzymes created by the fusion of a glucuronan lyase (TrGL) and a chitinase (ThCHIT42) from Trichoderma sp. have been constructed with the aim to validate a proof of concept regarding the potential of the chimera lyase/hydrolase by analyzing the functionality and the efficiency of the chimeric constructions compared to parental enzymes. All the chimeric enzymes, including or nor linker (GGGGS), were shown functional with activities equivalent or higher to native enzymes. The velocity of glucuronan lyase was considerably increased for chimeras, and may involved structural modifications at the active site. The fusion has induced a slightly decrease of the thermostability of glucuronan lyase, without modifying its catalytic activity regarding pH variations ranging from 5 to 8. The biochemical properties of chitinase seemed to be more disparate between the different fusion constructions suggesting an impact of the linkers or structural interactions with the linked glucuronan lyase. The chimeric enzymes displayed a decreased stability to temperature and pH variations, compared to parental one. Overall, TrGL-ThCHIT42 offered the better compromise in terms of biochemical stability and enhanced activity, and could be a promising candidate for further experiments in the field of fungi Cell Wall-Degrading Enzymes (CWDEs). Keywords: chitinase; glucuronan lyase; bifunctional enzyme; enzymatic efficiency; polysaccharide 1. Introduction The filamentous fungi belonging to Trichoderma genus have been considered with interest for their use as enzymatic producer for biocontrol strategies [1]. The antagonistic actions exerted by Trichoderma against fungal phytopathogens involve indirect mechanisms, such as competition for nutrients or space, modification of environmental conditions, induction of plant defensive properties and antibiosis, or directly mechanisms encompassing mycoparasitism [2,3]. The production and secretion by Trichoderma of Cell-Wall Degrading Enzymes (CWDEs), among which chitinases [4,5], glucanases [6–8] and proteases [9–11] are the most representative, playing a major and significant role in targeted host invasion [12,13]. Chitinases are polysaccharide hydrolases categorized into glycoside hydrolase (GH) 18, 19, 20, 23 and 48 families of the CAZy database (http://www.cazy.org/). They catalyze the hydrolysis of β-(1,4) linkages in chitin (Figure1), an abundant polysaccharide, found as a major structural compound of fungi cell wall [14,15]. Chitins are polymers composed of β(1,4) linked N-acetyl-d-glucosamine (GlcpNAc) Life 2020, 10, 234; doi:10.3390/life10100234 www.mdpi.com/journal/life LifeLife2020 2020, 10, 10, 234, x FOR PEER REVIEW 2 of2 of15 15 compound of fungi cell wall [14,15]. Chitins are polymers composed of β(1,4) linked and glucosamine (GlcpN). Native chitins include up to 90% of GlcpNAc in their structure. When the N‐acetyl‐D‐glucosamine (GlcpNAc) and glucosamine (GlcpN). Native chitins include up to 90% of degree of acetylation of chitin is lower than 40%, the term chitosan is used. However, authors use rather GlcpNAc in their structure. When the degree of acetylation of chitin is lower than 40%, the term thechitosan “deacetylation is used. However, degree” toauthors characterize use rather chitosans. the “deacetylation Chitinases havedegree” been to classifiedcharacterize in twochitosans. groups: EndochitinasesChitinases have (E.C.3.2.1.14) been classified which in two cleave groups: chitin Endochitinases at internal sites (E.C.3.2.1.14) forming dimeric which orcleave low molecularchitin at massinternal multimers sites forming of N-acetyl-glucosamine dimeric or low molecular (GlcNAc) mass (chitotriose,multimers of chitotetraose),N‐acetyl‐glucosamine and exochitinases (GlcNAc) comprising(chitotriose, both chitotetraose), chitobiosidases and (E.C.3.2.1.52)exochitinases catalyzing comprising the releaseboth chitobiosidases of di-acetylchitobioside (E.C.3.2.1.52) from thecatalyzing non-reducing the release end of chitin,of di‐acetylchitobioside and β-(1,4)-N-acetylglucosaminidases from the non‐reducing (GlcNAcases) end of chitin, (E.C.3.2.1.52) and generatingβ‐(1,4)‐N‐acetylglucosaminidases monomers of GlcNAc from (GlcNAcases) the products (E.C.3.2.1.52) of endochitinase generating and monomers chitobiosidase of GlcNAc [16]. If from many GlcNAcasesthe products (Nag1, of endochitinase Exc2, Tvnag1 and andchitobiosidase -2, Chit73, [16]. Chit102) If many identified GlcNAcases from (Nag1,T. harzanium Exc2, Tvnag1, T. atroviride and , T.‐2, asperellum Chit73, Chit102)and T. reesei identified[12,17, 18from] were T. harzanium known to, beT. functionallyatroviride, T. activeasperellum on chitin and T. degradation reesei [12,17,18] during mycoparasitism:were known to be some functionally of them, suchactive as on Nag1 chitin and degradation Chit102, were during also mycoparasitism: involved in the inductionsome of them, of the expressionsuch as Nag1 of other and Chit102, chitinolytic were enzymes also involved in presence in the of induction pathogen of [ 19the]. expression In addition, of the other over-expression chitinolytic byenzymesTrichoderma in presencespp. of of endochitinases pathogen [19]. Chit33,In addition, Chit36 the and over Chit42,‐expression originally by Trichoderma characterized spp. from of T.endochitinases harzanium [20 ],Chit33, significantly Chit36 enhanced and Chit42, antagonistic originally activity characterized of transformants from T. against harzaniumRhizoctonia [20], solanisignificantly, Fusarium enhanced oxysporum antagonisticand Sclerotium activity rolfsii of[ 9transformants,21,22], with chit42 against considered Rhizoctonia as asolani key, enzyme. Fusarium oxysporum and Sclerotium rolfsii [9,21,22], with chit42 considered as a key enzyme. FigureFigure 1. 1. ChitinaseChitinase and glucuronan lyase mechanism mechanism (with (with R R == HH and/or and/or acetyl acetyl group). group). AmongAmong the the enzymes enzymes produced produced by Trichodermaby Trichodermaand secreted and secreted in extracellular in extracellular medium, medium, a glucuronan a lyaseglucuronan (E.C.4.2.2.14) lyase (E.C.4.2.2.14) was purified was and purified characterized and characterized from Trichoderma from Trichodermasp. GL2 [ 23sp.,24 GL2]. This [23,24]. lyase cleavesThis lyase randomly cleaves glucuronan randomly glucuronan polysaccharide, polysaccharide, a polymer a of polymerβ-(1-4)-linked of β‐(1‐d4)-glucuronic‐linked D‐glucuronic acids, by a βacids,-elimination by a β‐elimination mechanism mechanism to produce to unsaturated produce unsaturated oligoglucuronans oligoglucuronans (Figure 1(Figure). Although 1). Although its role remainsits role unknown,remains unknown, several hypotheses several hypotheses might be might considered, be considered, notably the notably contribution the contribution of glucuronan of lyasesglucuronan in the assimilationlyases in the of assimilation celluloses which of celluloses are oxidized which by are lytic oxidized polysaccharide by lytic monooxygenasespolysaccharide (LPMO)monooxygenases produced from(LPMO) bacteria produced and fungi from [ 25bacteria]. Another and hypothesis fungi [25]. mayAnother be to hypothesis consider this may enzyme be to as aconsider CWDE. Althoughthis enzyme glucuronan as wasa CWDE. mainly describedAlthough as exopolysaccharidesglucuronan was inmainly several described bacteria [ 26as,27 ], fragmentsexopolysaccharides of glucuronan in several polysaccharides bacteria [26,27], were alsofragments reported of glucuronan as a representative polysaccharides cell-wall were component also ofreported specific phytopathogensas a representative belonging cell‐wall to Mucorales, component such of asspecificMucor andphytopathogensRhizopus genus belonging [28,29]. to Mucorales,Chitinase such and as glucuronan Mucor and Rhizopus lyase enzymes genus [28,29]. could then be attractive as potential biocontrol agent. SeveralChitinase arguments and glucuronan can be advanced lyase enzymes for their could potential then be interest attractive in as reducing potential fungi biocontrol development: agent. iSeveral chitin and arguments glucuronan can arebe advanced both components for their ofpotential the cell interest wall of in some reducing phytopathogens fungi development: (Mucorales), i) iichitin chitinase and glucuronan have been demonstrated are both components antagonistic of the agent cell wall against of some fungi, phytopathogens and iii the anti-fungal (Mucorales), properties ii) ofchitinase glucuronan have lyase been have demonstrated never been studied.antagonistic Moreover, agent theagainst rise offungi, genetic and engineering