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Higher eukaryotes have many distinct esterases. Among the different types are those which act on carboxylic esters (EC 3.1.1.-). Carboxyl-esterases have been classified into three categories (A, B and C) on the basis of differential patterns of inhibition by organophosphates. The sequence of a number of type-B carboxylesterases indicates [1,2,3] that the majority are evolutionary related. This family currently consists of the following proteins:

• Acetylcholinesterase (EC 3.1.1.7) (AChE) from vertebrates and from Drosophila.
• Mammalian cholinesterase II (butyryl cholinesterase) (EC 3.1.1.8). Acetylcholinesterase and cholinesterase II are closely related enzymes that hydrolyze choline esters [4].
• Mammalian liver microsomal carboxylesterases (EC 3.1.1.1).
• Drosophila esterase 6, produced in the anterior ejaculatory duct of the male insect reproductive system where it plays an important role in its reproductive biology.
• Drosophila esterase P.
• Culex pipiens (mosquito) esterases B1 and B2.
• Myzus persicae (peach-potato aphid) esterases E4 and FE4.
• Mammalian bile-salt-activated lipase (BAL) [5], a multifunctional lipase which catalyzes fat and vitamin absorption. It is activated by bile salts in infant intestine where it helps to digest milk fats.
• Insect juvenile hormone esterase (JH esterase) (EC 3.1.1.59).
• Lipases (EC 3.1.1.3) from the fungi Geotrichum candidum and Candida rugosa.
• Caenorhabditis gut esterase (gene ges-1).
• Duck acyl-[acyl-carrier protein] hydrolase, medium chain (EC 3.1.2.14), an enzyme that may be associated with peroxisome proliferation and may play a role in the production of 3-hydroxy fatty acid diester pheromones.
• Membrane enclosed crystal proteins from slime mold. These proteins are, most probably esterases; the vesicles where they are found have therefore been termed esterosomes.

So far two bacterial proteins have been found to belong to this family:

• Phenmedipham hydrolase (phenylcarbamate hydrolase), an Arthrobacter oxidans plasmid-encoded enzyme (gene pcd) that degrades the phenylcarbamate herbicides phenmedipham and desmedipham by hydrolyzing their central carbamate linkages.
• Para-nitrobenzyl esterase from Bacillus subtilis (gene pnbA).

The following proteins, while having lost their catalytic activity, contain a domain evolutionary related to that of carboxylesterases type-B:

• Thyroglobulin (TG), a glycoprotein specific to the thyroid gland, which is the precursor of the iodinated thyroid hormones thyroxine (T4) and triiodo thyronine (T3).
• Drosophila protein neurotactin (gene nrt) which may mediate or modulate cell adhesion between embryonic cells during development.
• Drosophila protein glutactin (gene glt), whose function is not known.

As is the case for lipases and serine proteases, the catalytic apparatus of esterases involves three residues (catalytic triad): a serine, a glutamate or aspartate and a histidine. The sequence around the active site serine is well conserved and can be used as a signature pattern. As a second signature pattern, we selected a conserved region located in the N-terminal section and which contains a cysteine involved in a disulfide bond.

Human esterase-D, also a type-B carboxylesterase, does not seem to be evolutionary related.

Sussman J.

April 2006 / Pattern revised.

PROSITE methods (with tools and information) covered by this documentation:

CARBOXYLESTERASE_B_1, PS00122; Carboxylesterases type-B serine active site  (PATTERN)

Consensus pattern: F-[GR]-G-x(4)-[LIVM]-x-[LIV]-x-G-x-S-[STAG]-G S is the active site residue Sequences known to belong to this class detected by the pattern: ALL members of this family with a catalytic activity Other sequence(s) detected in Swiss-Prot: NONE.

• Retrieve an alignment of Swiss-Prot true positive hits:   Clustal format, color, condensed view  / Clustal format, color  / Clustal format, plain text  / Fasta format • Retrieve the sequence logo from the alignment • Taxonomic tree view of all Swiss-Prot/TrEMBL entries matching PS00122 • Retrieve a list of all Swiss-Prot/TrEMBL entries matching PS00122 • Scan Swiss-Prot/TrEMBL entries against PS00122 • view ligand binding statistics

Matching PDB structures: 1ACJ 1ACL 1AKN 1AMN ... [ALL]

CARBOXYLESTERASE_B_2, PS00941; Carboxylesterases type-B signature 2  (PATTERN)

Consensus pattern: [EDA]-[DG]-C-L-[YTF]-[LIVT]-[DNS]-[LIV]-[LIVFYW]-x-[PQR] C is involved in a disulfide bond Sequences known to belong to this class detected by the pattern: ALL, except for mosquito and peach-potato aphid esterases and juvenile hormone esterases Other sequence(s) detected in Swiss-Prot: NONE.

• Retrieve an alignment of Swiss-Prot true positive hits:   Clustal format, color, condensed view  / Clustal format, color  / Clustal format, plain text  / Fasta format • Retrieve the sequence logo from the alignment • Taxonomic tree view of all Swiss-Prot/TrEMBL entries matching PS00941 • Retrieve a list of all Swiss-Prot/TrEMBL entries matching PS00941 • Scan Swiss-Prot/TrEMBL entries against PS00941 • view ligand binding statistics

Matching PDB structures: 1ACJ 1ACL 1AKN 1AMN ... [ALL]

1	Authors	Myers M., Richmond R.C., Oakeshott J.G.
	Title	On the origins of esterases.
	Source	Mol. Biol. Evol. 5:113-119(1988).
	PubMed ID	3163407

2	Authors	Krejci E., Duval N., Chatonnet A., Vincens P., Massoulie J.
	Title	Cholinesterase-like domains in enzymes and structural proteins: functional and evolutionary relationships and identification of a catalytically essential aspartic acid.
	Source	Proc. Natl. Acad. Sci. U.S.A. 88:6647-6651(1991).
	PubMed ID	1862088

3	Authors	Cygler M., Schrag J.D., Sussman J.L., Harel M., Silman I., Gentry M.K., Doctor B.P.
	Title	Relationship between sequence conservation and three-dimensional structure in a large family of esterases, lipases, and related proteins.
	Source	Protein Sci. 2:366-382(1993).
	PubMed ID	8453375

4	Authors	Lockridge O.
	Title	Structure of human serum cholinesterase.
	Source	BioEssays 9:125-128(1988).
	PubMed ID	3067729

5	Authors	Wang C.-S., Hartsuck J.A.
	Title	Bile salt-activated lipase. A multiple function lipolytic enzyme.
	Source	Biochim. Biophys. Acta 1166:1-19(1993).
	PubMed ID	8431483

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