REVIEW pubs.acs.org/CR The Metabolic Serine Hydrolases and Their Functions in Mammalian Physiology and Disease Jonathan Z. Long* and Benjamin F. Cravatt* The Skaggs Institute for Chemical Biology and Department of Chemical Physiology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States CONTENTS 2.4. Other Phospholipases 6034 1. Introduction 6023 2.4.1. LIPG (Endothelial Lipase) 6034 2. Small-Molecule Hydrolases 6023 2.4.2. PLA1A (Phosphatidylserine-Specific 2.1. Intracellular Neutral Lipases 6023 PLA1) 6035 2.1.1. LIPE (Hormone-Sensitive Lipase) 6024 2.4.3. LIPH and LIPI (Phosphatidic Acid-Specific 2.1.2. PNPLA2 (Adipose Triglyceride Lipase) 6024 PLA1R and β) 6035 2.1.3. MGLL (Monoacylglycerol Lipase) 6025 2.4.4. PLB1 (Phospholipase B) 6035 2.1.4. DAGLA and DAGLB (Diacylglycerol Lipase 2.4.5. DDHD1 and DDHD2 (DDHD Domain R and β) 6026 Containing 1 and 2) 6035 2.1.5. CES3 (Carboxylesterase 3) 6026 2.4.6. ABHD4 (Alpha/Beta Hydrolase Domain 2.1.6. AADACL1 (Arylacetamide Deacetylase-like 1) 6026 Containing 4) 6036 2.1.7. ABHD6 (Alpha/Beta Hydrolase Domain 2.5. Small-Molecule Amidases 6036 Containing 6) 6027 2.5.1. FAAH and FAAH2 (Fatty Acid Amide 2.1.8. ABHD12 (Alpha/Beta Hydrolase Domain Hydrolase and FAAH2) 6036 Containing 12) 6027 2.5.2. AFMID (Arylformamidase) 6037 2.2. Extracellular Neutral Lipases 6027 2.6. Acyl-CoA Hydrolases 6037 2.2.1. PNLIP (Pancreatic Lipase) 6028 2.6.1. FASN (Fatty Acid Synthase) 6037 2.2.2. PNLIPRP1 and PNLIPR2 (Pancreatic 2.6.2. ACOT1À6 (Acyl-CoA Thioesterases 1À6) 6038 Lipase-Related Proteins 1 and 2) 6028 2.7. Cholinesterases 6039 2.2.3. CEL (Carboxyl Ester Lipase) 6028 3. Peptidases 6041 2.2.4. LIPF (Gastric Lipase) 6029 3.1. PREP (Prolyl Endopeptidase) 6041 2.2.5. LPL (Lipoprotein Lipase) 6029 3.2. PREPL (Prolyl Endopeptidase-like) 6041 2.2.6. LIPC (Hepatic Lipase) 6029 3.3. DPP4 (Dipeptidyl Peptidase 4) 6042 2.2.7. LIPA (Lysosomal Acid Lipase) 6030 3.4. FAP (Fibroblast Activation Protein) 6042 2.2.8. LCAT (LecithinÀCholesterol 3.5. DPP8 and DPP9 (Dipeptidyl Peptidase 8 and 9) 6042 Acyltransferase) 6030 3.6. APEH (Acylpeptide Hydrolase) 6043 2.3. Phospholipase A2 Enzymes 6030 3.7. CTSA (Cathepsin A) 6043 2.3.1. PLA2G4A (Cytosolic PLA2) 6030 3.8. PRCP (Prolylcarboxypeptidase) 6044 2.3.2. PLA2G4BÀF (Cytosolic PLA2βÀζ) 6031 3.9. DPP7 (Dipeptidyl Peptidase 7) 6044 2.3.3. PLA2G6 (Calcium-Independent PLA2) 6032 4. Protein- and Glycan-Modifying Hydrolases 6044 2.3.4. PNPLA8 (Calcium-Independent PLA2γ) 6032 4.1. Protein Hydrolases 6044 2.3.5. PNPLA6 (Neuropathy Target Esterase) 6032 4.1.1. PPME1 (Protein Phosphate 2.3.6. PNPLA3 (Adiponutrin) 6033 Methylesterase 1) 6044 2.3.7. PLA2G7 (Plasma Platelet-Activating 4.1.2. LYPLA1 and LYPLA2 (Lysophospholipase Factor Acetylhydrolase) 6033 1 and 2) 6045 2.3.8. PAFAH2 (Platelet-Activating Factor 4.1.3. PPT1 and PPT2 (Protein Palmitoyl 6045 Acetylhydrolase 2) 6033 Thioesterase 1 and 2) 2.3.9. PAFAH1b2 and PAFAH1b3 (Type Ib Platelet-Activating Factor Special Issue: 2011 Lipid Biochemistry, Metabolism, and Signaling Acetylhydrolases 2 and 3) 6034 Received: March 10, 2011 2.3.10. PLA2G15 (Lysosomal PLA2) 6034 Published: June 23, 2011 r 2011 American Chemical Society 6022 dx.doi.org/10.1021/cr200075y | Chem. Rev. 2011, 111, 6022–6063 Chemical Reviews REVIEW 4.2. Glycan Hydrolases 6046 cleave ester, amide, or thioester bonds in small molecules, 1 4.2.1. AOAH (Acyloxyacyl Hydrolase) 6046 peptides, or proteins. The serine proteases have been the subject 2À5 4.2.2. PGAP1 (Post-GPI Attachment Protein 1) 6047 of several books and reviews. This article will instead focus on the metabolic SHs (Figure 1). 4.2.3. SIAE (Sialic Acid Acetylesterase) 6047 The nucleophilicity of the active site serine of metabolic SHs 5. Partially Characterized Hydrolases and Emerging arises from its participation in a catalytic dyad (e.g., Ser-Lys or Methods for Their Investigation 6048 Ser-Asp) or triad (e.g., Ser-His-Asp or Ser-Ser-Lys).6,7 The SH 5.1. Representative Examples of Poorly catalytic mechanism proceeds by formation of an acyl-enzyme Characterized Hydrolases 6048 intermediate at the active site serine, followed by water-induced fi 5.1.1. AADAC and AADACL2 and 4 (Aryl saponi cation of the product, and regeneration of the free serine residue for entry into the next reaction cycle (Figure 2).8,9 Owing Acetamide Deacetylase and Aryl to the enhanced reactivity of the active site serine, the functional Acetamide Deacetylase-like 2 and 4) 6048 state of most SHs can be assessed using active-site directed 5.1.2. ABHD1, ABHD2, and ABHD3 (Alpha/Beta affinity labels such as fluorophosphonates (FPs, Figure 2).1,10 Hydrolase Domain Containing 1, 2, and 3) 6048 The serine nucleophile of metabolic SHs is generally, though not 5.1.3. ABHD11 (Alpha/Beta Hydrolase Domain exclusively embedded within a GXSXG motif and a majority these R β Containing 11) 6049 enzymes adopt an / hydrolase fold that consists of a central β-sheet surrounded by R-helicies (Figure 2).11 SHs also encompass 5.1.4. ABHD14B (Alpha/Beta Hydrolase Domain other smaller subsets of structurally distinct enzymes such as the Containing 14B) 6049 phospholipase A2s, the amidase signature enzymes, and the 5.1.5. BPHL (Biphenyl Hydrolase-like Protein) 6049 dipeptidylpeptidases.12,13 Metabolic SHs have been shown to parti- 5.1.6. SEC23IP (Sec23p-Interacting Protein) 6049 cipate in virtually all (patho)physiological processes in mammals, 14 15 16 5.1.7. OVCA2 (Ovarian Tumor Suppressor including neurotransmission, metabolism, pain sensation, inflammation,17 oxidative stress,18 cancer,19 and bacterial infection.20 Candidate 2) 6049 Many excellent reviews have described the structure and À 5.1.8. RBBP9 (Retinablastoma-Binding function of individual SHs.15,19,21 23 Here, we attempt to Protein 9) 6049 provide a comprehensive summary that captures our state of 5.1.9. PNLIPRP1 (Pancreatic Lipase-Related knowledge about mammalian metabolic SHs in their entirety, Protein 1) 6049 including those enzymes that remain mostly or completely 5.1.10. LACTB (Serine β-Lactamase-like Protein) 6050 uncharacterized. Particular emphasis will be placed on relating the biochemistry and enzymology of individual SHs to the 5.1.11. PNPLA5 (Patatin-like Phospholipase physiological substrates and products that they regulate in living Domain Containing 5) 6050 systems, and how SHs, through the regulation of specific meta- 5.1.12. SCPEP1 and CPVL (Serine bolic pathways impact health and disease. If selective and Carboxypeptidase 1 and efficacious inhibitors are available for a particular SH, we will Carboxypeptidase, Vitellogenic-like) 6050 also include a discussion of their use. The majority of this review will be organized by substrate class. Later, we will discuss SHs for 5.2. Chemoproteomic and Metabolomic Platforms which putative endogenous substrates have not been identified, for Functional Assignment of Poorly as well as emerging chemoproteomic and metabolomic methods Characterized Hydrolases 6050 aimed at assigning functions to these enzymes. For the sake of 5.2.1. Chemoproteomic Platforms for Discovery consistency, we have elected to refer to SHs by their proper gene and Optimization of SH Inhibitors 6050 names throughout this review (rather than their common name 5.2.2. Specialized ABPP Probes That Mimic SH or abbreviation) but have also attempted to include other aliases where appropriate. Substrate Classes 6051 5.2.3. Untargeted Metabolomics and 2. SMALL-MOLECULE HYDROLASES Peptidomics for SH Substrate Discovery 6051 The largest category of substrates for metabolic SHs is small 6. Summary and Key Outstanding Questions 6052 molecules, which include neutral fatty acyl esters, acyl thioesters Author Information 6053 (e.g., acyl CoAs), phospholipids, lipid amides, and other ester Biographies 6053 metabolites (e.g., acetylcholine). As will be described in this Acknowledgment 6054 section, the small molecules themselves may be structural com- References 6054 ponents of cells and tissues, as is the case for some phospholipids, or important stores of energy, as is the case for triglycerides, or signaling molecules, as is the case for acetylcholine. 2.1. Intracellular Neutral Lipases 1. INTRODUCTION Intracellular triglyceride and cholesteryl ester stores in organs Serine hydrolases (SHs) consist of > 200 enzymes in humans such as adipose tissue and brain are hydrolyzed by multiple SHs, characterized by the presence of an active site serine that is used including LIPE, PNPLA2, MGLL, and DAGLR and β (Figure 3). for the hydrolysis of substrates. The membership of this enzyme The resultant free fatty acid products are an important fuel in class is near-equally split between serine proteases (trypsin/ mammals and can be converted by the β-oxidation pathway to chymotrypsin/subtilisin enzymes) and “metabolic” SHs that acetyl-CoA, which can enter the citric acid cycle for oxidative 6023 dx.doi.org/10.1021/cr200075y |Chem. Rev. 2011, 111, 6022–6063 Chemical Reviews REVIEW Figure 1. Dendrogram showing the primary sequence alignment of the human mammalian metabolic SHs, where alignment was generated by anchoring sequences at the site of their catalytic Ser residues. phosphorylation to generate ATP. These hydrolytic reactions endogenous substrates for LIPE.30 Taken together, these data also generate signaling molecules, such as the neuromodulatory suggest that LIPE participates in the second step of TG lipolysis lipid 2-arachidonoylglycerol (2-AG), which activates cannabi- in adipose tissue by hydrolyzing DG in vivo. noid receptors. Several chemical classes of synthetic LIPE inhibitors have been 2.1.1. LIPE (Hormone-Sensitive Lipase). In humans, LIPE, described, including carbamates,33 heterocyclic ureas,34,35 and also called hormone-sensitive lipase (HSL), is an 84 kDa intra- pyrrolopyrazinediones,36 although their selectivity and pharma- cellular enzyme predominantly expressed in adipocytes and cological effects in mammals have not been extensively reported.