Major urinary proteins, despite their misleading names, are unimportant losers. They used to just be plain urinary proteins until they had the great idea to add "Major" to their names in order to augment their popularity. This plan backfired, since all the other proteins already knew that they were losers and only grew to detest them more. It was such a spectacular failure of a plan that they earned a quick trip into the legendary annals of total loserdom.
Currently, the major urinary proteins still totally suck.
The major urinary proteins had it off tough from the very beginning. They were derided by all the other proteins the moment they evolved for their gawky molecular structure, pasty amino complexion, and fervent love of Magic: The Gathering. Each felt isolated and alone, despite their best efforts to fit in; they were quickly isolated from all the existing subfamilies. Only one urinary protein, Terrence Ag14, scored it in with the sweat proteins as a wingman. The outcasts drifted towards each other and lifelong chemical bonds began to form, united only in their loneliness and skill at fantasy card games.
While their isolation was the likely result of the shallowness of the other proteins, evolution has not been kind to the proteins, whose bitterness has grown to condescending proportions. While the other families of proteins were genial towards each other and frequently mingled in the bloodstream, the urinary proteins remained cliquey and aloof. They attempted to turn their nature as outcasts into a boon, like Big Boi and Andre 3000 before them, but instead they just became colossal assholes.
They are very good at transporting urine. Surprisingly, this hasn't helped their reputation much. A digestive enzyme named Sally Cv72, who developed from the same gland as several of the major urinary proteins, said that she was, in fact, rather impressed with their skill at transporting urine. Nevertheless, she was more interested in proteins with flat abs, or sensitive enzymes who wrote poetry. While transporting urine may not have earned them many friends, the gift of molecular wheels made them prime choices for performing odd jobs around the body, particularly during the "wet" seasons of summer and winter. Typically, these jobs were performed with an audible sneer and they were never hired back again.
A couple major urinary proteins have attempted to act as pheromones in order to attract the attention of some hot chicks. While successful in attracting attention, surprisingly, the chicks all saw through their clever facade and turned them down. Being covered in pee might not have helped their case much.
Many people are allergic to major urinary proteins. Though no specific cause has been pinned down, data suggests it is because the proteins themselves are allergic to lots of things, most notably peanuts. "What goes around comes around," said esteemed urologist Washington Irving at the 2006 TED Talks, "leave it to those snide little bastards to leave their ailment on our doorsteps."
Though the exact nature of major urinary proteins is still under careful scrutiny, little more than what is already known can be discovered about those chumps. Despite their own hopes that their functions are evolving and have yet to truly blossom, a long-term study conducted by the Rensselaer Polytechnic Institute suggests that, to paraphrase Sam Cooke, "a change ain't gonna come." An analysis of a MUP's structure suggests that its fervent passion for yo-yos and fantasy card games is inherent to its essential carboxyl group, while six amino acids that make up the common MUP also cause chronic acne and back-hair in proteins.
The study totally slammed the MUPs, but it hasn't bruised their egos one bit. The few that have the aminos to actually approach girls tell them they'll lose the carboxyl group when they're in high school and only keep evolving in college. These MUPs are only fooling themselves. If only they knew that the girls can't stop laughing about them once they waddle away! As if they'd start forming peptide bonds with losers instead of the hunky 13-cis Retinoic Acids on the lacrosse team.