ABSTRACT
Covalent modification of NTE, a neuronal protein with serine esterase activity, by certain organophosphates (OP) initiates degeneration of long axons in the peripheral and central nervous system. Simple inhibition of NTE esterase activity does not initiate neuropathy; the latter requires aging of the OP bound to the catalytic serine residue so that a negatively-charged species is left attached to the active site. This may indicate that a non-esterase function of NTE is important for axonal maintenance. We have recently cloned NTE and shown that it is unrelated to any known serine hydrolases but contains a novel C-terminal domain which is conserved from bacteria to man. Furthermore, the catalytic serine is located within this domain at the centre of a helical hydrophobic segment of the polypeptide's secondary structure. The integrity of NTE would be severely compromised by the presence of a negatively-charged organophosphate moiety at this site. Implications for possible higher-order structures and functions for NTE are discussed.
Subject(s)
Carboxylic Ester Hydrolases/genetics , Carboxylic Ester Hydrolases/isolation & purification , Binding Sites , Brain/enzymology , Carboxylic Ester Hydrolases/metabolism , Catalysis , Cloning, Molecular , Humans , Serine/genetics , Serine/metabolismABSTRACT
The N-terminal amino acid sequences of proteolytic fragments of neuropathy target esterase (NTE), covalently labelled on its active-site serine by a biotinylated organophosphorus ester, were determined and used to deduce the location of this serine residue and to initiate cloning of its cDNA. A putative NTE clone, isolated from a human foetal brain cDNA library, encoded a 1327 residue polypeptide with no homology to any known serine esterases or proteases. The active-site serine of NTE (Ser-966) lay in the centre of a predicted hydrophobic helix within a 200-amino-acid C-terminal domain with marked similarity to conceptual proteins in bacteria, yeast and nematodes; these proteins may comprise a novel family of potential serine hydrolases. The Swiss Cheese protein which, when mutated, leads to widespread cell death in Drosophila brain [Kretzschmar, Hasan, Sharma, Heisenberg and Benzer (1997) J. Neurosci. 17, 7425-7432], was strikingly homologous to NTE, suggesting that genetically altered NTE may be involved in human neurodegenerative disease.
Subject(s)
Carboxylic Ester Hydrolases/chemistry , Drosophila Proteins , Neurodegenerative Diseases/genetics , Serine Endopeptidases/chemistry , Amino Acid Sequence , Animals , Binding Sites/physiology , Biotin/analogs & derivatives , Biotin/metabolism , Brain/pathology , Cloning, Molecular , Conserved Sequence , Evolution, Molecular , Humans , Molecular Sequence Data , Mutation/genetics , Nerve Tissue Proteins/chemistry , Nerve Tissue Proteins/genetics , Organophosphorus Compounds/metabolism , Protein Structure, Secondary , Sequence Analysis, DNA , Sequence Homology, Amino AcidABSTRACT
A gene (ESS1) predisposing to the development of multiple invasive but self-healing skin tumours (squamous cell epitheliomata) is tightly linked to the polymorphic DNA marker D9S53 (9q31) with a maximum lod score of 9.02 at a recombination fraction of 0.03. Multipoint linkage analysis demonstrates that the disease locus is most likely to lie between D9S58 (9q22.3-31) and ASSP3 (9q11-q22). Comparison of markers associated with ESS1 in independently ascertained families suggests a common origin of the disease and defines the location of ESS1. Haplotype studies indicate that the disease locus is most likely to lie between D9S29 (9q31) and D9S1 (9q22.1-q22.2).
