Amino Acid Sequence of Horse Serum Butyrylcholinesterase

Abstract

Horse serum butyrylcholinesterase (Eq-BChE) has been shown to be an effective pretreatment drug (bio-scavenger) for organophosphate toxicity in mice and rhesus monkeys. In addition, it has the longest mean retention time in animals among all ChE preparations tested. We now report the complete amino acid sequence of this protein (Figure 1). The tetrameric form of Eq-BChE was purified and subjected to fragmentation by cyanogen bromide, trypsin, and endo Arg-C protease. Digests were fractionated by reverse phase HPLC, and isolated peptides were sequenced by automated Edman degradation. Overlapping peptides were used to determine sequence order. Like other BChEs it is composed of 574 amino acids. Eight carbohydrate modified sites were found at amino acids 57, 106, 241, 256, 341, 455, 481, and 486 as N-linked Asn residues. The active site charge-relay triad amino acids were Glu325, Ser198 and His438. The N-terminal amino acids were Glu-Glu-Asp-Ile, consistent with this being the mature form of the enzyme. Eq-BChE has a high degree of primary sequence identity to human BChE, 90.1%, but has one less N-glycosylation site and Cys residue. If conserved amino acid substitutions are included, the proteins share 93.4% homology.