A non-structural pure enzyme protein forms a LCST type of stimuli-responsive and reversible hydrogel with novel structure and catalytic activity

Abstract

Hydrogels have a wide range of applications such as in biomedicine, cosmetics and soft electronics. Compared to polymer hydrogels based on covalent bonding, protein hydrogels offer distinct advantages owing to their biocompatibility and better access to molecular engineering. However, pure and natural protein hydrogels have been seldom reported except for structural proteins like collagen and silk fibrin. Here, we report the unusual ability and mechanism of a unique natural enzyme, lipoate-protein ligase A (LplA) of E. coli to self-assemble into a stimuli-responsive and reversible hydrogel of the low critical solution temperature (LCST) type. This is the first globular and catalytic protein found to form a hydrogel in response to temperature, pH and the presence of ions. Protein structure based analysis reveals the key residues responsible for the gel formation and mutational studies confirms the essential roles of hydrogen bonding between the C-terminal domains and electrostatic interactions in the N-terminal domains. Characterization of phase transitions of wild type LplA and its mutants using small angle X-ray scattering (SAXS) yields details of the gelation process from initial dimer formation over a pre-gel-state to full network development. Further electron microscopic analyses and modeling of SAXS data suggest an unusual interlinked ladder-like structure of the macroscopic crosslinking network with dimers as ladder steps. The unique features of this first reported protein hydrogel may open up hitherto inaccessible applications, especially those taking advantage of the inherent catalytic activity of LplA.

Enzyme immobilization in hydrogels: A perfect liaison for efficient and sustainable biocatalysis

“…Natural polymers are de quo composed of mostly polysaccharides (e.g., agarose, alginate, carrageenan, cellulose, chitosan, hyaluronic acid, and starch) or proteins (e.g., collagen, fibrin, and gelatin) [ 77 , 78 , 79 ]. The advantage of these materials is that they are inherently biocompatible, are non‐toxic, biodegradable, mechanically flexible, and renewable.…”

Chemically programed nucleic condensates for spatiotemporal control of mammalian gene expression

“…1A). First, we show that an Escherichia coliderived lipoate-protein ligase A (LplA 33 ) not only forms stable condensate structures in mammalian cells, but can also be flexibly tethered to different cellular compartments (i.e. the nucleus, mitochondria and plasma membrane) in a trigger-inducible manner upon fusion to specific conditional protein dimerization systems.…”