Bioengineered Approaches for Site Orientation of Peptide-Based Ligands of Nanomaterials

Successful application of nanoconjugates either in vitro or in vivo does depend on the design strategy used for their development. In this chapter, we focus on the most important factors that need to be taken into account to optimize nanoparticle biofunctionalization and provide an overview of recent approaches yielding the efficient and orientation-controlled immobilization of complex molecules, including peptides and proteins. In addition, we discuss on the elements that cooperate with ligand orientation in affecting the biological activity of nanoconjugates. Indeed, the control of ligand orientation on the nanoparticle surface is of crucial importance in determining the affinity of the immobilized biomolecules toward the biological target. However, the ability of a nanoconjugate to recognize its target is even strongly affected by other important items, including (1) multivalency as a result of ligand density and organization; (2) conformational changes potentially occurring on binding of ligands to the nanoparticle; (3) thermodynamic and kinetic factors related to the interaction of the ligand with the nanoparticle surface; and (4) interaction between nanoparticle and its surrounding environment to form the so-called "protein corona." Altogether, these five issues are the driving force in the specificity and selectivity of designed nanoconjugates toward their target, and, as a consequence, define their potential utility for biomedical application. Therefore, a careful control on the abovementioned "magic five" contributions is needed to improve the quality standard of the next-generation nanomedicines. In addition to the illustrated nanobioconjugation strategies, we emphasize that all these features need to be carefully optimized when assessing the biological effects of synthetic nanoparticles designed for biomedical purposes.