Abstract
The venom of the snake Bungarus fasciatus contains a hydrophilic, monomeric species of acetylcholinesterase (AChE), characterized by a C-terminal region that does not resemble the alternative T- or H-peptides. Here, we show that the snake contains a single gene for AChE, possessing a novel alternative exon (S) that encodes the C-terminal region of the venom enzyme, located downstream of the T exon. Alternative splicing generates S mRNA in the venom gland and S and T mRNAs in muscle and liver. We found no evidence for the presence of an H exon between the last common "catalytic" exon and the T exon, where H exons are located in Torpedo and in mammals. Moreover, COS cells that were transfected with AChE expression vectors containing the T exon with or without the preceding genomic region produced exclusively AChET subunits. In the snake tissues, we could not detect any glycophosphatidylinositol-anchored AChE form that would have derived from H subunits. In the liver, the cholinesterase activity comprises both AChE and butyrylcholinesterase components; butyrylcholinesterase corresponds essentially to nonamphiphilic tetramers and AChE to nonamphiphilic monomers (G1na). In muscle, AChE is largely predominant: it consists of globular forms (G1a and G4a) and trace amounts of asymmetric forms (A8 and A12), which derive from AChET subunits. Thus, the Bungarus AChE gene possesses alternatively spliced T and S exons but no H exon; the absence of an H exon may be a common feature of AChE genes in reptiles and birds.
Highlights
The venom of the snake Bungarus fasciatus contains a hydrophilic, monomeric species of acetylcholinesterase (AChE), characterized by a C-terminal region that does not resemble the alternative T- or H-peptides
The cloning of AChE from Bungarus venom revealed, that this homology is limited to the catalytic domain and that the C-terminal sequence is entirely different from both C-terminal H- and T-peptides, which are encoded by alternatively spliced exons in the single AChE gene and characterize AChEH and AChET subunits of other vertebrates
The presence of the SARA sequence, replacing the H or T sequences, which are encoded by alternative exons in Torpedo and mammalian AChE genes, raises the problem of the relationship between the venom enzyme and the AChE molecules that occur in cholinergic synapses of the snake
Summary
The venom of the snake Bungarus fasciatus contains a hydrophilic, monomeric species of acetylcholinesterase (AChE), characterized by a C-terminal region that does not resemble the alternative T- or H-peptides. The cloning of AChE from Bungarus venom revealed, that this homology is limited to the catalytic domain and that the C-terminal sequence is entirely different from both C-terminal H- and T-peptides, which are encoded by alternatively spliced exons in the single AChE gene and characterize AChEH and AChET subunits of other vertebrates (review in Ref. 1). Lated to the fact that the venom AChE possesses a specific C-terminal peptide, which we called SARA after its last four residues: this peptide is highly hydrophilic and does not contain any cysteine residue that could establish intersubunit disulfide bonds It defines AChES subunits, which produce only soluble monomers when expressed in COS cells [7]. Readthrough transcripts are expected to produce nonamphiphilic, monomeric AChE, but the corresponding proteins have never been characterized in vivo
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
