Structure of the Brain N-Acetylaspartate Biosynthetic Enzyme NAT8L Revealed by Computer Modeling

Conformational Stability and Denaturation Processes of Proteins Investigated by Electrophoresis under Extreme Conditions

The functional structure of proteins results from marginally stable folded conformations. Reversible unfolding, irreversible denaturation, and deterioration can be caused by chemical and physical agents due to changes in the physicochemical conditions of pH, ionic strength, temperature, pressure, and electric field or due to the presence of a cosolvent that perturbs the delicate balance between stabilizing and destabilizing interactions and eventually induces chemical modifications. For most proteins, denaturation is a complex process involving transient intermediates in several reversible and eventually irreversible steps. Knowledge of protein stability and denaturation processes is mandatory for the development of enzymes as industrial catalysts, biopharmaceuticals, analytical and medical bioreagents, and safe industrial food. Electrophoresis techniques operating under extreme conditions are convenient tools for analyzing unfolding transitions, trapping transient intermediates, and gaining insight into the mechanisms of denaturation processes. Moreover, quantitative analysis of electrophoretic mobility transition curves allows the estimation of the conformational stability of proteins. These approaches include polyacrylamide gel electrophoresis and capillary zone electrophoresis under cold, heat, and hydrostatic pressure and in the presence of non-ionic denaturing agents or stabilizers such as polyols and heavy water. Lastly, after exposure to extremes of physical conditions, electrophoresis under standard conditions provides information on irreversible processes, slow conformational drifts, and slow renaturation processes. The impressive developments of enzyme technology with multiple applications in fine chemistry, biopharmaceutics, and nanomedicine prompted us to revisit the potentialities of these electrophoretic approaches. This feature review is illustrated with published and unpublished results obtained by the authors on cholinesterases and paraoxonase, two physiologically and toxicologically important enzymes.

Engineering of a critical membrane-anchored enzyme for high solubility and catalytic activity

Membrane-associated proteins carry out a wide range of essential cellular functions but the structural characterization needed to understand these functions is dramatically underrepresented in the Protein Data Bank. Producing a soluble, stable and active form of a membrane-associated protein presents formidable challenges, as evidenced by the variety of approaches that have been attempted with a multitude of different membrane proteins to achieve this goal. Aspartate N-acetyltransferase (ANAT) is a membrane-anchored enzyme that performs a critical function, the synthesis of N-acetyl-l-aspartate (NAA), the second most abundant amino acid in the brain. This amino acid is a precursor for a neurotransmitter, and alterations in brain NAA levels have been implicated as a causative effect in Canavan disease and has been suggested to be involved in other neurological disorders. Numerous prior attempts have failed to produce a soluble form of ANAT that is amenable for functional and structural investigations. Through the application of a range of different approaches, including fusion partner constructs, linker modifications, membrane-anchor modifications, and domain truncations, a highly soluble, stable and fully active form of ANAT has now been obtained. Producing this modified enzyme form will accelerate studies aimed at structural characterization and structure-guided inhibitor development.