Properties, Structure, and Applications of Microbial Sterol Esterases
Total Page：16
File Type：pdf, Size：1020Kb
Appl Microbiol Biotechnol (2016) 100:2047–2061 DOI 10.1007/s00253-015-7258-x MINI-REVIEW Properties, structure, and applications of microbial sterol esterases Maria Eugenia Vaquero1 & Jorge Barriuso1 & María Jesús Martínez1 & Alicia Prieto1 Received: 11 November 2015 /Revised: 14 December 2015 /Accepted: 17 December 2015 /Published online: 7 January 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract According to their substrate preferences, carboxylic and purification, heterologous expression, structure, stability, ester hydrolases are organized in smaller clusters. Among or substrate specificity, which are the main properties that them, sterol esterases (EC 3.1.1.13), also known as cholesterol make them attractive for different applications. Moreover, a esterases, act on fatty acid esters of cholesterol and other ste- comprehensive phylogenetic analysis on available sequences rols in aqueous media, and are also able to catalyze synthesis of cholesterol esterases has been done, including putative se- by esterification or transesterification in the presence of organ- quences deduced from public genomes. ic solvents. Mammalian cholesterol esterases are intracellular enzymes that have been extensively studied since they are Keywords Sterol esterase . Biocatalysts . Hydrophobic essential in lipid metabolism and cholesterol absorption, and enzymes . Bacteria . Fungi the natural role of some microbial sterol esterases is supposed to be similar. However, besides these intracellular enzymes, a number of microbes produce extracellular sterol esterases, Introduction which show broad stability, selectivity, or wide substrate spec- ificity, making them interesting for the industry. In spite of Carboxylic ester hydrolases (EC 3.1.1) are a large class of this, there is little information about microbial sterol esterases, enzymes catalyzing the hydrolysis or synthesis of ester bonds. and only a small amount of them have been characterized. Their ecological and physiological relevance can be deduced Some of the most commercially exploited cholesterol ester- from the fact that they have been described in all life domains, ases are produced by Pseudomonas species and by Candida prokaryotic and eukaryotic (Levisson et al. 2009), as intra- or rugosa, although in the last case they are usually described extracellular proteins. But besides this, many of them are ex- and named as Bhigh substrate versatility lipases.^ From a ceptionally robust catalysts able of acting under conditions structural point of view, most of them belong to the α/β-hy- drastically different from those of their natural environment, drolase superfamily and have a conserved Bcatalytic triad^ for example in the presence of organic solvents (Villeneuve formed by His, an acidic amino acid and a Ser residue that is et al. 2005). This is the reason why this group includes the located in a highly conserved GXSXG sequence. In this re- biocatalysts with the highest number of industrial applications view, the information available on microbial sterol esterases such as lipolytic enzymes, used in an array of sectors as oils has been gathered, taking into account their origin, production and fats, detergents, bakery, cheese, textile, leather and paper, etc. (Jaeger and Reetz 1998; Hasan et al. 2006). From a struc- tural point of view, most of them belong to the α/β-hydrolase * María Jesús Martínez superfamily and have a conserved Bcatalytic triad^ formed by [email protected] His, an acidic amino acid and a Ser residue that is located in a * Alicia Prieto highly conserved GXSXG sequence. During hydrolysis, the [email protected] catalytic Ser will start the nucleophilic attack of the substrate helped by the other two residues from the triad, which are in 1 Centro de Investigaciones Biológicas, Consejo Superior de close spatial vicinity. These are presumed to facilitate the Investigaciones Científicas, Madrid, Spain hydrolysis of esters by a mechanism similar to that of 2048 Appl Microbiol Biotechnol (2016) 100:2047–2061 chymotrypsin-like serine proteases (Appel 1986). Another Table 1 Sources of microbial sterol esterases characteristic feature is the presence of an amino acidic region Organism Reference whose sequence is not as conserved as that of the catalytic triad, the oxyanion hole, which serves to stabilize a transition Bacteria state generated during catalysis. In addition, these enzymes Acinetobacter Du et al. (2010) generally do not require cofactors. B. cepacia Takeda et al. (2006) According to their substrate preferences, carboxylic ester C. trachomatis Peters et al. (2012) hydrolases are organized in smaller clusters. Among them, C. viscosum Kontkanen et al. (2004) sterol esterases (EC 3.1.1.13), also known as cholesterol es- P. aeruginosa Sugihara et al. (2002) terases, act on fatty acid esters of cholesterol and other sterols P. fluorescens Uwajima and Terada (1976) in aqueous media, and are also able to catalyze their synthesis P. mendocina Svendsen et al. (1995) by esterification or transesterification in the presence of organ- P. pseudoalcaligenes Svendsen et al. (1995) ic solvents (Weber et al. 2001). As explained above, they are S. aureus Harvie (1977) widespread in nature and have been identified from mammals’ Streptomyces sp. Xiang et al. (2006) tissues such as the pancreas, intestinal mucosa, liver, placenta, S. avermitilis Xiang et al. (2007) aorta, and brain (Brockerhoff and Jensen 1974;Masand S. griseus Xiang et al. (2007) Lombardo 1994), to filamentous fungi, yeast, and bacteria S. lavendulae Kamei et al. (1979) (Kaiser et al. 1994;Sugiharaetal.2002). Fungi Mammalian cholesterol esterases have been extensively C. rugosa Rúa et al. (1993) studied and their role is mainly related to lipid metabolism F. oxysporum Okawa and Yamaguchi (1977) and cholesterol absorption (Rudd and Brockman 1984; M. albomyces Kontkanen et al. (2006c) Mukherjee 2003). They usually contain over 500 amino acid N. haematococca Vaquero et al. (2015b) residues, with a molecular mass >60 kDa, and the catalytic Ser O. piceae Calero-Rueda et al. (2002b) residue is included in the GESAG sequence. Microbial sterol P. glomerata Pollero et al. (2001) esterases are supposed to play a similar function as their mam- Trichoderma sp. Maeda et al. (2008) mals’ counterparts, and their natural role could be related to T. reesei Vaquero et al. (2015b) lipid metabolism and use of lipids as carbon sources. For example, one of the few reports on these enzymes demon- strates that three membrane-anchored lipases with sterol ester- ase activity from Saccharomyces cerevisiae are essential to maintain the sterols homeostasis in vivo (Köffel et al. 2005). structures correspond to sterol esterases from the prokaryotes Similarly, after a large screening for sterol esterase and lipase Burkholderia glumae and Chromobacterium viscosum, the activities in Aspergillus spp., the GRAS strains Aspergillus yeast Candida rugosa (three isoforms) (Grochulski et al. oryzae NRRL 6270 and Aspergillus sojae NRRL 6271 1993, 1994; Ghosh et al. 1995;Mancheñoetal.2003), and showed to produce intracellular enzymes with homology to the filamentous fungus Ophiostoma piceae (Gutiérrez- those of S. cerevisiae, with a very similar signal-anchor motif Fernández et al. 2014 ). Two common structural features of for type III membrane proteins (Töke et al. 2007). these proteins are also shared by lipases. Firstly, the existence Besides the intracellular sterol esterases, some microbes of a lid covering the active site whose displacement is promot- secrete these enzymes to the environment. This is the case of ed in the presence of a substrate or interface, and secondly, several plant pathogens or saprophytes, in which the function their tendency to form aggregates. This owes to their highly of these extracellular esterases is mostly related to degradation hydrophobic character, which in turn is necessary for estab- of target compounds from plant envelopes (Juniper and Jeffree lishing interactions with very hydrophobic substrates. This 1983). In general, the secreted enzymes show broad stability, property can make difficult the purification and characteriza- selectivity, or wide substrate specificity, making them interest- tion of these proteins, and even induce to mistakes on their ing for the industry (Jaeger and Reetz 1998). In spite of this, molecular mass assignation if measured under non-denaturing there is little information about microbial sterol esterases, and conditions, since the calculated value may correspond to a only a small amount of them have been characterized. This is protein aggregate. the reason of the paucity of protein sequences and structural In terms of substrate specificity, many sterol esterases are information available for deducing general features beyond able to catalyze the hydrolysis or synthesis of a rather broad those described for other carboxyl ester hydrolases. A list range of other substrates containing ester linkages, such as of extracellular microbial sterol esterases is summarized acylglycerols, aryl esters (Gray et al. 1992; Svendsen et al. in Table 1. Some of them have been isolated and char- 1995; Calero-Rueda et al. 2002b; Kontkanen et al. 2006c; acterized, although without structural details, and the known Du et al. 2010), and in some cases alcohol esters, cinnamyl Appl Microbiol Biotechnol (2016) 100:2047–2061 2049 esters, xhantophyl esters (Zorn et al. 2005; Maeda et al. 2008), Gutiérrez et al. 2009). However, this enzyme preparation lacks or synthetic polymers (Barba Cedillo et al. 2013b).