Abstract
Lysenin is a pore-forming protein extracted from the earthworm Eisenia fetida, which inserts large conductance pores in artificial and natural lipid membranes containing sphingomyelin. Its cytolytic and hemolytic activity is rather indicative of a pore-forming toxin; however, lysenin channels present intricate regulatory features manifested as a reduction in conductance upon exposure to multivalent ions. Lysenin pores also present a large unobstructed channel, which enables the translocation of analytes, such as short DNA and peptide molecules, driven by electrochemical gradients. These important features of lysenin channels provide opportunities for using them as sensors for a large variety of applications. In this respect, this literature review is focused on investigations aimed at the potential use of lysenin channels as analytical tools. The described explorations include interactions with multivalent inorganic and organic cations, analyses on the reversibility of such interactions, insights into the regulation mechanisms of lysenin channels, interactions with purines, stochastic sensing of peptides and DNA molecules, and evidence of molecular translocation. Lysenin channels present themselves as versatile sensing platforms that exploit either intrinsic regulatory features or the changes in ionic currents elicited when molecules thread the conducting pathway, which may be further developed into analytical tools of high specificity and sensitivity or exploited for other scientific biotechnological applications.
Highlights
Modulation of ionic currents may occur because of selectivity, existence of regulatory mechanisms that lead to conformational changes and conductance adjustments, and diminished ionic flows resulting from analyte binding or translocation through the pore [6,8,15,18,19,20]
While the results indicate that the wild-type channel and the engineered one have different properties with regards to translocation, more experimental evidence should be provided in support of the claim that lysenin successfully captures and facilitates translocation of DNA strands
To bring evidence of translocation, the investigatorsoftook long-term stability presented by large populations of lysenin channels reconstituted into planar lipid advantage of the long-term stability presented by large populations of lysenin channels reconstituted membranes
Summary
The ability of pore-forming proteins and peptides to establish conducting pathways between two sides of a lipid membrane was exploited for decades for numerous analytical applications [1,2,3,4,5,6,7,8,9]. Porins and pore-forming toxins present similar functionalities to ion channels in terms of creating transmembrane conducting pathways and ensuring high transport rates [16,26,27,28] They often lack selectivity and regulation, which might be an important characteristic for sensor development, they are amenable to chemical and genetic modifications aiming at introducing specific bio-recognition elements into their structure and changing their response to stimuli [5,13,16,19]. In the same line of conductance sensing capabilities, the physical large opening of lysenin and chemical identities of analytes, and include simple binding and partial occlusion, conformational channels and absence of vestibular constrictions recommends them as analytical tools for single changes to closed or sub-conducting states (ligand-induced gating), and gating and trapping of long molecule detection and characterization byline resistive pulse techniques sensing). Development of precise, highly sensitive, and specific sensors with single molecule identification and discrimination capabilities
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