Protein mimicry and the design of bioactive cell penetrating peptides: The genesis of STOPSPERM bioportides

Abstract

The mature spermatozoon, a highly differentiated cell equipped for the sole purpose of fertilisation, lacks the protein machinery required for conventional endocytotic mechanisms. Perhaps contrary to expectation, cell penetrating peptides (CPPs) rapidly translocate across the unique sperm plasma membrane to accrete within distinct intracellular compartments. Confocal microscopy, employing red-fluorescent CPPs and bioportides, is a convenient platform to study this membrane translocation process. In the virtual absence of genetic expression, rapid physiological responses of human sperm are dependent upon protein-protein interactions that may be regulated by post-translational modifications including phosphorylation. This chapter provides an outline of the design of bioactive CPPs, or bioportides, which include protein-mimetic sequences from the interaction domains of sperm proteins. Protocols are included which enable the biological assessment of the impact of bioportides upon the viability and motility of spermatozoa.