Application of zero-length cross-linking to form lysozyme, horseradish peroxidase and lysozyme–peroxidase dimers: Activity and stability

Synthesis of lysozyme-metallacarborane conjugates and the effect of boron cluster modification on protein structure and function

Two complementary methods, "in solution" and "in solid state", for the synthesis of lysozyme modified with metallacarborane (cobalt bis(dicarbollide), Co(C2 B9 H11 )2 (2-) ) were developed. As metallacarborane donors, oxonium adducts of cobalt bis(dicarbollide) and 1,4-dioxane or tetrahydropyran were used. The physicochemical and biochemical properties of the obtained lysozyme-metallacarborane conjugates were studied for changes in secondary and tertiary structure, aggregation behavior, and biological activity. Only minor changes in primary, secondary, and tertiary protein structure were observed, caused by the single substitution of metallacarborane on lysozyme. However, the modification produced significant changes in lysozyme enzymatic activity and a tendency toward time- and temperature-dependent aggregation.

Succinimidyl residue formation in hen egg-white lysozyme favors the formation of intermolecular covalent bonds without affecting its tertiary structure

Protein chemical degradations occur naturally into living cells as soon as proteins have been synthesized. Among these modifications, deamidation of asparagine or glutamine residues has been extensively studied, whereas the intermediate state, a succinimide derivative, was poorly investigated because of the difficulty of isolating those transient species. We used an indirect method, a limited thermal treatment in the dry state at acidic pH, to produce stable cyclic imide residues in hen lysozyme molecules, enabling us to examine the structural and functional properties of so modified proteins. Five cyclic imide rings have been located at sites directly accessible to solvent and did not lead to any changes in secondary or tertiary structures. However, they altered the catalytic properties of lysozyme and significantly decreased the intrinsic stability of the molecules. Moreover, dimerization occurred during the treatment, and this phenomenon was proportional to the extent of chemical degradation. We propose that succinimide formation could be responsible for covalent bond formation under specific physicochemical conditions that could be found in vivo.