Molecular and cellular biology of cholinesterases

Linkages between cholinesterases and the pharmacological sciences extend back to the mid-nineteenth century when the first organophosphate was synthesized (1) and physostigmine was recognized in the western world for possessing pharmacological activity (2). However, not until Sir Henry Dale (3) delineated two components of the cholinergic nervous system was the suggestion made that physostigmine inhibited an enzyme that catalyzed the breakdown of choline esters. Dale's and later Loewi & Navratil's (4) studies established a role for acetylcholine as a labile neurotransmitter. The high turnover number of acetylcholinesterase (AChE), the specificity of its inhibitors, and the selectivity of thiocholine-metal ion interactions provided the bases for sensitive in vitro and in situ assay systems (5-7). Several cholinesterase inhibitors remain of value as medicinal agents and insecticides, but others possess the potential for insidious use as chemical warfare agents (8). Despite this long history of study, less than a decade has passed since the primary structure of a cholinesterase was determined (9), and only in 1991 was its crystal structure solved (10). Clearly, these recent events have added a new perspective to cholinesterase research wherein all facets of gene expression become amenable to study and structure-function relation­ ships within this family of enzymes can be approached at an atomic level

The Cholinesterases: From Genes to Proteins

Based on the recently determined X-ray structures of Torpedo californica acetylcholinesterase and Geotrichum candidum lipase and on their three-dimensional superposition, an improved alignment of a collection of 32 related amino acid sequences of other esterases, lipases, and related proteins was obtained. On the basis of this alignment, 24 residues are found to be invariant in 29 sequences of hydrolytic enzymes, and an additional 49 are well conserved. The conservation in the three remaining sequences is somewhat lower. The conserved residues include the active site, disulfide bridges, salt bridges, and residues in the core of the proteins. Most invariant residues are located at the edges of secondary structural elements. A clear structural basis for the preservation of many of these residues can be determined from comparison of the two X-ray structures.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/pro.5560020309

Relationship between sequence conservation and three‐dimensional structure in a large family of esterases, lipases, and related proteins

The cellular slime mold Dictyostelium discoideum undergoes a transition from single-celled amoebae to a multicellular organism as a natural part of its life cycle. A method of cell-cell signaling that controls chemotaxis, morphogenesis, and gene expression has developed in this organism, and a detailed understanding of this signaling system provides clues to mechanisms of intercellular communication in the development of metazoans.

https://science.sciencemag.org/content/sci/245/4922/1054.full.pdf

Dictyostelium discoideum: a model system for cell-cell interactions in development

Periodicspikesof decreasedoptical density wererecorded incell suspensions ofDictyostelium discoideum. Spikeformation aswellaschangesinthe redoxstateofcytochrome b arefacultatively andinde- pendently coupledto an oscillating systemwhichis underdevelopmental control andpresumably underlies signal transmission inaggregating cells. Cyclic AMP triggers a doubleresponse, theslowcom- ponentresembling thespikes formedduringspontaneous oscillations. Thefastcomponentshowscharacteristics of thechemotactic iesponse tocyclic AMP. The receptor systemissuggested tosensechangesofcyclic AMP con- centration intime.Cyclic AMP pulses interact withthe oscillating system,resulting inphaseshift orsuppression ofspikeformation, andintheinduction ofoscillations in an earlystageofdevelopment before theonsetofspon- taneousoscillations. Continuous flowapplication ofcyclic AMP doesnotchangefrequency up toflowrateswhich extinguish oscillations.

Cyclic-AMP-Controlled Oscillations inSuspended Dictyostelium Cells: TheirRelation toMorphogenetic CellInteractions

cAMP regulation of early gene expression in signal transduction mutants of Dictyostelium

Molecular analysis of a developmentally regulated gene required for Dictyostelium aggregation.

We have examined the expression of a cAMP pulse-repressed and two cAMP pulse-induced genes in response to cAMP and caffeine under a number of different physiological conditions, and in several classes of development mutants altered in cAMP-mediated signal transduction pathways. The data presented help characterize the mutants with regard to early gene expression. Analysis of the data indicates that full induction of the pulse-induced or repression of the pulse-repressed genes requires cycles of activation and adaptation of the cAMP receptor but does not require a rise in intracellular cAMP. Comparison of the results obtained between different mutant classes suggests that repression and activation of the two classes of genes can be uncoupled, implying that different intracellular mechanisms control these processes. In addition, we examined the effects of caffeine and show that it can induce pulse-induced mRNA accumulation in the absence of cAMP.

Christopher Pinko

Papers

cAMP regulation of early gene expression in signal transduction mutants of Dictyostelium

Molecular analysis of a developmentally regulated gene required for Dictyostelium aggregation.

Control of early gene expression in Dictyostelium.

Regulation of Dictyostelium early gene expression in cAMP bypass mutants.