Contrary to lectins, and perhaps as an added advantage for semen nanopurification, ubiquitin recognizes not only spermatozoa with damaged acrosomes, but also those with other types of sperm head and tail defects, including cells with compromised DNA.32 During sperm maturation in the epididymis–a sperm storage gland attached to the testicular surface–abnormal spermatozoa are tagged on their surfaces by ubiquitin through the process of protein ubiquitination.3