In recent decades, protein-based therapeutics have substantially expanded the field of molecular pharmacology due to their outstanding potential for the treatment of disease. Unfortunately, protein pharmaceuticals display a series of intrinsic physical and chemical instability problems during their production, purification, storage, and delivery that can adversely impact their final therapeutic efficacies. This has prompted an intense search for generalized strategies to engineer the long-term stability of proteins during their pharmaceutical employment. Due to the well known effect that glycans have in increasing the overall stability of glycoproteins, rational manipulation of the glycosylation parameters through glycoengineering could become a promising approach to improve both the in vitro and in vivo stability of protein pharmaceuticals. The intent of this review is therefore to further the field of protein glycoengineering by increasing the general understanding of the mechanisms by which glycosylation improves the molecular stability of protein pharmaceuticals. This is achieved by presenting a survey of the different instabilities displayed by protein pharmaceuticals, by addressing which of these instabilities can be improved by glycosylation, and by discussing the possible mechanisms by which glycans induce these stabilization effects.

In the past several years, halogen bonds have been shown to be relevant in crystal engineering and biomedical applications. One of the reasons for the utility of these types of noncovalent interactions in the development of, for example, pharmaceutical ligands is that their strengths and geometric properties are very tunable. That is, substitution of atoms or chemical groups in the vicinity of a halogen can have a very strong effect on the strength of the halogen bond. In this study we investigate halogen-bonding interactions involving aromatically-bound halogens (Cl, Br, and I) and a carbonyl oxygen. The properties of these halogen bonds are modulated by substitution of aromatic hydrogens with fluorines, which are very electronegative. It is found that these types of substitutions have dramatic effects on the strengths of the halogen bonds, leading to interactions that can be up to 100% stronger. Very good correlations are obtained between the interaction energies and the magnitudes of the positive electrostatic potentials (σ-holes) on the halogens. Interestingly, it is seen that the substitution of fluorines in systems containing smaller halogens results in electrostatic potentials resembling those of systems with larger halogens, with correspondingly stronger interaction energies. It is also shown that aromatic fluorine substitutions affect the optimal geometries of the halogen-bonded complexes, often as the result of secondary interactions.

During their development and administration, protein-based drugs routinely display suboptimum therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular level strategies to improve the therapeutic behavior of protein drugs. Among, the currently developed approaches, glycoengineering is one of the most promising due fact that it has been shown to simultaneously afford improvements over most of the parameters necessary for optimization of protein drug in vivo efficacy (e.g., in vitro and in vivo molecular stability, pharmacodynamic responses, and pharmacokinetic profiles) while allowing for targeting to the desired site of action. The intent of this article is to provide an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and to describe the current understanding of the mechanisms by which glycosylation leads to such effects.

In a previous study we investigated the effects of aromatic fluorine substitution on the strengths of the halogen bonds in halobenzene…acetone complexes (halo = chloro, bromo, and iodo). In this work, we have examined the origins of these halogen bonds (excluding the iodo systems), more specifically, the relative contributions of electrostatic and dispersion forces in these interactions and how these contributions change when halogen σ-holes are modified. These studies have been carried out using density functional symmetry adapted perturbation theory (DFT-SAPT) and through analyses of intermolecular correlation energies and molecular electrostatic potentials. It is found that electrostatic and dispersion contributions to attraction in halogen bonds vary from complex to complex, but are generally quite similar in magnitude. Not surprisingly, increasing the size and positive nature of a halogen's σ-hole dramatically enhances the strength of the electrostatic component of the halogen bonding interaction. Not so obviously, halogens with larger, more positive σ-holes tend to exhibit weaker dispersion interactions, which is attributable to the lower local polarizabilities of the larger σ-holes.

Glycosylation constitutes one of the most important posttranslational modifications employed by biological systems to modulate protein biophysical properties. Due to the direct biochemical and biomedical implications of achieving control over protein stability and function by chemical means, there has been great interest in recent years towards the development of chemical strategies for protein glycosylation. Since current knowledge about glycoprotein biophysics has been mainly derived from the study of naturally glycosylated proteins, chemical glycosylation provides novel insights into its mechanistic understanding by affording control over glycosylation parameters. This review presents a survey of the effects that natural and chemical glycosylation have on the fundamental biophysical properties of proteins (structure, dynamics, stability, and function). This is complemented by a mechanistic discussion of how glycans achieve such effects and discussion of the implications of employing chemical glycosylation as a tool to exert control over protein biophysical properties within biochemical and biomedical applications.