Acetylcholinesterase of schistosoma mansoni—Functional correlates: Contributed in honor of Professor Hans Neurath's 90^th birthday

Abstract

Acetylcholinesterase~AChE! is an enzyme broadly distributed in many species, including parasites. It occurs in multiple molecular forms that differ in their quaternary structure and mode of anchoring to the cell surface. This review summarizes biochemical and immunological investigations carried out in our laboratories on AChE of the helmint, Schistosoma mansoni. AChE appears in S. mansoni in two principal molecular forms, both globular, with sedimentation coefficients of ;6.5 and 8 S. On the basis of their substrate specificity and sensitivity to inhibitors, both are "true" acetylcholinesterases. Approximately half of the AChE activity of S. mansoni is located on the outer surface of the parasite, attached to the tegumental membrane via a covalently attached glycosylphosphatidylinositol anchor. The remainder is located within the parasite, mainly associated with muscle tissue. Whereas the internal enzyme is most likely involved in termination of neurotransmission at cholinergic synapses, the role of the surface enzyme remains to be established; there are, however, indications that it is involved in signal transduction. The two forms of AChE differ in their heparin-binding properties, only the internal 8 S form of the AChE being retained on a heparin column. The two forms differ also in their immunological specificity, since they are selectively recognized by different monoclonal antibodies. Polyclonal antibodies raised against S. mansoni AChE purified by affinity chromatography are specific for the parasite AChE, reacting with both molecular forms, but do not recognize AChE from other species. They interact with the surface-localized enzyme on the intact organism, and produce almost total complement-dependent killing of the parasite. S. mansoni AChE is thus demonstrated to be a functional protein, involved in multifaceted activities, which can serve as a suitable candidate for diagnostic purposes, vaccine development, and drug design.

In vitro evaluation of the schistosomicidal effect of the extracts, fractions and major 3-hydroxy-2,6-dialkyl-substituted piperidine alkaloids from the flowers of Senna spectabilis (Fabaceae)

“…The other form is external, associated with the tegument, and involved in signal transduction. 35 Therefore, the function of ACh as a neurotransmitter is reinforced by the fact that the worm possesses enzymes for its synthesis and degradation. Additional evidence for the physiological role of ACh in S. mansoni is that muscular activity of this worm is reduced by cholinomimetic agents such as carbachol, nicotine and AChE inhibitors that produce flaccid paralysis, which can be defined as a loss of motility accompanied by worm elongation due to relaxation of its longitudinal musculature.…”

Vaccination withSchistosoma mansonicholinesterases reduces parasite burden and egg viability in a mouse model of schistosomiasis

“…It may be that there is some redundancy in the cholinergic functioning of these molecules (even BChEs, like SmBChE1, can perform a cholinergic role in situations of AChE deficiency [29]) and so collective inhibition of the molecules is required to produce a functional deficit. Also, given the multiple proposed functions for parasite ChEs [4,30], it is possible is that the neutralization of multiple enzymatic targets more profoundly interrupts varied processes of parasite biology than just cholinergic transmission.…”

“…Due to the fundamental roles they play in parasite biology (reviewed in [4], schistosome cholinesterases (SmChEs) have been posited as intervention targets against schistosomiasis and there are several indications to support the feasibility of their use as vaccines. Firstly, SmChEs have been localized to the tegument of schistosomula and adult worms [5,6] and anti-SmChE antibodies have been shown to bind to and kill schistosomula [7], suggesting that the enzymes are accessible to immune attack.…”

Novel cholinesterase paralogs ofSchistosoma mansonihave perceived roles in cholinergic signaling, glucose scavenging and drug detoxification and are essential for parasite survival

“…Cholinesterase (ChE) activity in S. mansoni was first described by Bueding in 1952 [33] and was well characterized biochemically in the four decades succeeding this discovery. The technological limitations of this time period meant that most of the evidence for SmChEs came from whole worm studies and analyses of crude parasite extracts (reviewed in [13]), which could not ascribe ChE activity to any particular protein. Several studies in the early 2000's characterized a single AChE from S. mansoni (Smp_154600 in the current gene annotation nomenclature) and its direct homolog in other species of schistosomes [14,15,21], but lack of a comprehensive schistosome genome annotation at the time precluded identification of more ChE family members.…”

“…While AChE activity has been documented extensively in S. mansoni (reviewed in [13]), most of the work has involved studies on parasite extracts or native SmChE purified by inhibitoraffinity chromatography, making it difficult to attribute function to any one particular SmChE molecule. Further, more recent, but still "pre-genomic", studies have documented only one AChE-encoding gene in S. mansoni and other species [14,15].…”