There are many storylines surrounding Saturday's upcoming middleweight fight between WBC, WBA, IBF and IBO champion Gennady "GGG" Golovkin and challenger Kell Brook at 02 Arena in London. Two very different boxers will be squaring off under unusual circumstances.

Just on the surface, the amount of experience and success both boxers have enjoyed makes the bout intriguing. Golovkin (35-0, 32 KOs) and Brook (36-0, 25 KOs) take their impressive boxing records into the ring and both enter with momentum. 

Golovkin, 34, is perhaps the most intimidating power puncher in the world, but he'll be facing an opponent who has looked particularly sharp in recent fights. Brook won his last two fights by TKO, defeated highly respected Jo Jo Dan in four rounds, and held off American star Shawn Porter by majority decision. 

"Kell's got no fear, unlike many who have fought Golovkin, who were beaten before they even climbed into the ring," Brook's promoter Eddie Hearn told BBC Sport.

Golovkin is listed as the favorite at -650, while Brook's odds are at +500. 

Here are five key facts ahead of the fight.

Brook Moves Up Weight Class

This is most notable story of the fight. Brook is taking a big chance by moving up in weight class and to battle perhaps the best pound-for-pound boxer in the world. The 30-year-old had previously fought at 147 pounds, but will take on Golovkin at 160 pounds. How Brook manages at his heaviest will be something to watch for. 

It's been 50 years since a welterweight champion won a middleweight title fight.

WBA Belt Not On The Line

The WBA has refused to sanction a title defense since Brook has never fought as a middleweight. Only Golovkin's WBC and IBF middleweight titles will be on the line. Meanwhile, Brook will retain his status as the IBF's welterweight champion.

GGG Fights In England

This will be the first time Golovkin may feel some discomfort when he approaches the ring, as Brook, who was born in Sheffield, will have the crowd on his side. The Kazakh has mostly fought in Los Angeles and New York in recent years, with a couple stops in Monte Carlo.

While Golovkin has a reputation for being a highly focused boxer, London crowds can be very vocal and at times intimidating, which could play a small role in the tone of the fight. 

"It’s no problem for me to come here," Golovkin said. "I can’t stay in Kazakhstan. I want more fights all over the world."

Two Undefeated Boxers

Brook has a good chin and his only knocked down was back in April 2007. But he's facing a boxer's hardest puncher, and one who hasn't gone the distance since an eight-round fight in June 2008. Golovkin did need 11 rounds to defeat Martin Murray by TKO in February 2015, but no boxer has given him serious concerns. Brook will need to be more defensive and find a way to dodge Golovkin's hard power punches to keep the fight competitive. 

Canelo Is Lurking

One high-profile boxer will have a keen interest in the result of the fight. Canelo Alvarez, arguably the biggest draw in boxing following the retirement of Floyd Mayweather, is expected to fight Golokvin in 2017, but all that can change depending on the outcome against Brook.

Should Brook win, a huge payday could await the Brit by fighting Alvarez. A convincing win for Golovkin could mean a megabout with Alvarez could be pushed back. There is growing sentiment that Golden Boy Promotions, which represents Alvarez, is hoping to hold off on signing a deal in order to build anticipation.